Bipolar disorder is commonly diagnosed during adolescence or early adulthood, but onset can occur throughout the life cycle. The disorder can be difficult to distinguish from unipolar depression and the average delay in diagnosis is 5–10 years after symptoms begin. Diagnosis of bipolar disorder takes several factors into account and considers the self-reported experiences of the symptomatic individual, abnormal behavior reported by family members, friends or co-workers, observable signs of illness as assessed by a clinician, and often a medical work-up to rule-out medical causes. In diagnosis, caregiver-scored rating scales, specifically the mother, has been found to be more accurate than teacher and youth report in predicting identifying youths with bipolar disorder. Assessment is usually done on an outpatient basis; admission to an inpatient facility is considered if there is a risk to oneself or others. The most widely used criteria for diagnosing bipolar disorder are from the American Psychiatric Association's (APA) "Diagnostic and Statistical Manual of Mental Disorders", Fifth Edition (DSM-5) and the World Health Organization's (WHO) "International Statistical Classification of Diseases and Related Health Problems", 10th Edition (ICD-10). The ICD-10 criteria are used more often in clinical settings outside of the U.S. while the DSM criteria are used clinically within the U.S. and are the prevailing criteria used internationally in research studies. The DSM-5, published in 2013, included further and more accurate specifiers compared to its predecessor, the DSM-IV-TR. Semi structured interviews such as the Kiddie Schedule for Affective Disorders and Schizophrenia (KSADS) and the Structured Clinical Interview for DSM-IV (SCID) are used for diagnostic confirmation of bipolar disorder.

Several rating scales for the screening and evaluation of bipolar disorder exist, including the Bipolar spectrum diagnostic scale, Mood Disorder Questionnaire, the General Behavior Inventory and the Hypomania Checklist. The use of evaluation scales cannot substitute a full clinical interview but they serve to systematize the recollection of symptoms. On the other hand, instruments for screening bipolar disorder tend to have lower sensitivity.

Psychosis as a symptom of a psychiatric disorder is first and foremost a diagnosis of exclusion. So a new-onset episode of psychosis "cannot" be considered to be a symptom of a psychiatric disorder until other relevant and known medical causes of psychosis are excluded, or ruled out. Many clinicians improperly perform, or entirely miss this step, introducing avoidable diagnostic error and misdiagnosis.

An initial assessment includes a comprehensive history and physical examination. Although no biological laboratory tests exist which confirm schizoaffective disorder, biological tests should be performed to exclude psychosis associated with or caused by substance use, medications, toxins or poisons, surgical complications, or other medical illnesses. Since non-medical mental health practitioners are not trained to exclude medical causes of psychosis, people experiencing psychosis should be referred to an emergency department or hospital.

Delirium should be ruled out, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, indicating other underlying factors which includes medical illnesses. Excluding medical illnesses associated with psychosis is performed by using blood tests to measure:

- Thyroid-stimulating hormone to exclude hypo- or hyperthyroidism,

- Basic electrolytes and serum calcium to rule out a metabolic disturbance,

- Full blood count including ESR to rule out a systemic infection or chronic disease, and

- Serology to exclude syphilis or HIV infection.

Other investigations which may be performed include:

- EEG to exclude epilepsy, and an

- MRI or CT scan of the head to exclude brain lesions.

Blood tests are not usually repeated for relapse in people with an established diagnosis of schizoaffective disorder, unless there is a specific "medical" indication. These may include serum BSL if olanzapine has previously been prescribed, thyroid function if lithium has previously been taken to rule out hypothyroidism, liver function tests if chlorpromazine has been prescribed, CPK levels to exclude neuroleptic malignant syndrome, and a urinalysis and serum toxicology screening if substance use is suspected. Assessment and treatment may be done on an outpatient basis; admission to an inpatient facility is considered if there is a risk to self or others.

Because psychosis may be precipitated or exacerbated by common classes of psychiatric medications, such as antidepressants, ADHD stimulant medications, and sleep medications, prescribed medication-induced psychosis should be ruled out, particularly for first-episode psychosis. This is an essential step to reduce diagnostic error and to evaluate potential medication sources of further patient harm. Regarding prescribed medication sources of patient harm, Yale School of Medicine Professor of Psychiatry Malcolm B. Bowers, Jr, MD wrote:

Illicit drugs aren't the only ones that precipitate psychosis or mania—prescribed drugs can too, and in particular, some psychiatric drugs. We investigated this and found that about 1 in 12 psychotic or manic patients in an inpatient psychiatric facility are there due to antidepressant-induced psychosis or mania. That's unfortunate for the field [of psychiatry] and disastrous for some of our patients.

Substance-induced psychosis should also be ruled out. Both substance- and medication-induced psychosis can be excluded to a high level of certainty while the person is psychotic, typically in an emergency department, using both a

- Broad spectrum urine toxicology screening, and a

- Full serum toxicology screening (of the blood).

Some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests. So a psychotic person's family, partner, or friends should be asked whether he or she is currently taking any dietary supplements.

Common mistakes made when diagnosing psychotic patients include:

- Not properly excluding delirium,

- Missing a toxic psychosis by not screening for substances "and" medications,

- Not appreciating medical abnormalities (e.g., vital signs),

- Not obtaining a medical history and family history,

- Indiscriminate screening without an organizing framework,

- Not asking family or others about dietary supplements,

- Premature diagnostic closure, and

- Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder.

Only after these relevant and known causes of psychosis have been ruled out can a psychiatric differential diagnosis be made. A mental health clinician will incorporate family history, observation of a psychotic person's behavior while the person is experiencing active symptoms, to begin a psychiatric differential diagnosis. Diagnosis also includes self-reported experiences, as well as behavioral abnormalities reported by family members, friends, or significant others. Mistakes in this stage include:

- Not screening for dissociative disorders. Dissociative identity disorder and psychotic symptoms in schizoaffective disorder have considerable overlap, yet a different overall treatment approach.

Accurately assessing for a specific Depressive Disorder diagnosis requires an expenditure of time that is deemed unreasonable for most primary care physicians. For this reason, physicians often use this code as a proxy for a more thorough diagnosis. There is concern that this may lead to a "wastebasket" mindset for certain disorders. In addition reimbursement through Medicare may be lower for certain non specific diagnosis.

The most widely used criteria for diagnosing schizoaffective disorder are from the American Psychiatric Association's "Diagnostic and Statistical Manual of Mental Disorders-5".

The DSM-IV schizoaffective disorder definition was plagued by problems of being inconsistently (or unreliably) used on patients; when the diagnosis is made, it doesn't stay with most patients over time; and it has questionable diagnostic validity (that is, it doesn't describe a distinct disorder, nor predict any particular outcome). These problems have been slightly reduced (or "modestly improved") in the DSM-5 according to Carpenter.

When psychotic symptoms are confined to an episode of mania or depression (with or without mixed features), the diagnosis is that of a “psychotic” mood disorder, namely either bipolar disorder or major depression). Only when psychotic states persist in a sustained fashion for two weeks or longer without concurrent affective symptoms is the diagnosis schizoaffective disorder or schizophrenia.

The second cardinal guideline in the DSM-5 diagnosis of schizoaffective disorder is one of timeframe.

These two changes are intended by the DSM-5 workgroup to accomplish two goals:

- Increase the diagnosis' consistency (or reliability) when it is used;

- Significantly decrease the overall use of the schizoaffective disorder diagnosis.

If the schizoaffective diagnosis is used less often, other diagnoses (like psychotic mood disorders and schizophrenia) are likely to be used more often; but this is hypothetical until real-world data arrive. Validity problems with the diagnosis remain and await further work in the fields of psychiatric genetics, neuroimaging, and cognitive science that includes the overlapping fields of cognitive, affective, and social neuroscience, which may change the way schizoaffective disorder is conceptualized and defined in future versions of the DSM and ICD.

Most people who meet criteria for bipolar disorder experience a number of episodes, on average 0.4 to 0.7 per year, lasting three to six months. "Rapid cycling", however, is a course specifier that may be applied to any of the above subtypes. It is defined as having four or more mood disturbance episodes within a one-year span and is found in a significant proportion of individuals with bipolar disorder. These episodes are separated from each other by a remission (partial or full) for at least two months or a switch in mood polarity (i.e., from a depressive episode to a manic episode or vice versa). The definition of rapid cycling most frequently cited in the literature (including the DSM) is that of Dunner and Fieve: at least four major depressive, manic, hypomanic or mixed episodes are required to have occurred during a 12-month period. Ultra-rapid (days) and ultra-ultra rapid or ultradian (within a day) cycling have also been described. The literature examining the pharmacological treatment of rapid cycling is sparse and there is no clear consensus with respect to its optimal pharmacological management.

Diagnosis of cyclothymia is difficult for a number of reasons. The depressive-dysthymic episode of cyclothymia is also a diagnostic feature of many disorders, including adjustment disorders, personality disorders, psychotic disorders, and other mood disorders. Since depression can be triggered or exacerbated by life events and circumstances, the diagnosing clinician must determine when it is an acceptable response and when it is pathological.

Symptoms described in the hypomanic episode are also commonly associated with ADHD, such as increased energy, distractibility and impulsive or risk-seeking behavior. This is of particular concern in child psychiatry because symptoms, especially hyperactivity, may be counted twice toward both disorders or may inflate the prevalence of ADHD.

While childhood ADHD often presents with hyperactivity, adult ADHD often does not. The unstable lifestyle often found both in people with ADHD and in those with cyclothymia can cause problems for differential diagnosis. Important distinguishing factors include that ADHD is characterized mainly by problems with concentration and memory, while cyclothymia mainly by periods of elevated self-confidence and elation.

Whether subtypes of bipolar disorder, such as cyclothymia truly represent separate disorders or are part of a unique bipolar spectrum is still debated in research. Cyclothymia is typically not described in research studies or diagnosed in clinical settings, making it less recognizable and less understood by professionals. This absence of cyclothymia in research and clinical settings suggests that cyclothymia is either being diagnosed as another mood disorder or as a non-affective psychiatric disorder or not coming to scientific or clinical attention due to a lack of diagnostic clarity or because the nature of cyclothymia is still highly contested. Additionally, the current diagnostic criterion for cyclothymia emphasizes that symptoms are persistent, which suggests that they are enduring traits rather than a psychological state, thus, it has been argued that it should be diagnosed as a personality disorder. Since the symptoms tend to overlap with personality disorders, the validity and distinction between these two diagnostic categories has been debated.

Lastly, the tendency of cyclothymia to be comorbid with other mental disorders makes diagnosis difficult. These issues prevent consensus on the definition of cyclothymia and its relationship with other mental disorders among researchers and clinicians. This lack of consensus on an operational definition and symptom presentation is especially pronounced with children and adolescents because the diagnostic criteria have not been adequately adapted to take into account their developmental level. However, there has been a shift from categorical models of bipolar related disorders toward a dimensional model, which is intended to address some of these issues.

This disorder is common in the relatives of patients with bipolar disorder, and some individuals with cyclothymia eventually develop bipolar disorder themselves. It may persist throughout adult life, cease temporarily or permanently, or develop into more severe mood swings, meeting the criteria for bipolar disorder or recurrent depressive disorder in some cases.

Though there is no clear-cut way to prevent dysthymia from occurring, some suggestions have been made. Since dysthymia will often first occur in childhood, it is important to identify children who may be at risk. It may be beneficial to work with children in helping to control their stress, increase resilience, boost self-esteem, and provide strong networks of social support. These tactics may be helpful in warding off or delaying dysthymic symptoms.

A diagnostic assessment may be conducted by a suitably trained general practitioner, or by a psychiatrist or psychologist, who records the person's current circumstances, biographical history, current symptoms, and family history. The broad clinical aim is to formulate the relevant biological, psychological, and social factors that may be impacting on the individual's mood. The assessor may also discuss the person's current ways of regulating mood (healthy or otherwise) such as alcohol and drug use. The assessment also includes a mental state examination, which is an assessment of the person's current mood and thought content, in particular the presence of themes of hopelessness or pessimism, self-harm or suicide, and an absence of positive thoughts or plans. Specialist mental health services are rare in rural areas, and thus diagnosis and management is left largely to primary-care clinicians. This issue is even more marked in developing countries. The mental health examination may include the use of a rating scale such as the Hamilton Rating Scale for Depression or the Beck Depression Inventory or the Suicide Behaviors Questionnaire-Revised. The score on a rating scale alone is insufficient to diagnose depression to the satisfaction of the DSM or ICD, but it provides an indication of the severity of symptoms for a time period, so a person who scores above a given cut-off point can be more thoroughly evaluated for a depressive disorder diagnosis. Several rating scales are used for this purpose.

Primary-care physicians and other non-psychiatrist physicians have more difficulty with underrecognition and undertreatment of depression compared to psychiatric physicians, in part because of the physical symptoms that often accompany depression, in addition to the many potential patient, provider, and system barriers that the authors describe. A review found that non-psychiatrist physicians miss about two-thirds of cases, though this has improved somewhat in more recent studies.

Before diagnosing a major depressive disorder, in general a doctor performs a medical examination and selected investigations to rule out other causes of symptoms. These include blood tests measuring TSH and thyroxine to exclude hypothyroidism; basic electrolytes and serum calcium to rule out a metabolic disturbance; and a full blood count including ESR to rule out a systemic infection or chronic disease. Adverse affective reactions to medications or alcohol misuse are often ruled out, as well. Testosterone levels may be evaluated to diagnose hypogonadism, a cause of depression in men. Vitamin D levels might be evaluated, as low levels of vitamin D have been associated with greater risk for depression.

Subjective cognitive complaints appear in older depressed people, but they can also be indicative of the onset of a dementing disorder, such as Alzheimer's disease. Cognitive testing and brain imaging can help distinguish depression from dementia. A CT scan can exclude brain pathology in those with psychotic, rapid-onset or otherwise unusual symptoms. In general, investigations are not repeated for a subsequent episode unless there is a medical indication.

No biological tests confirm major depression. Biomarkers of depression have been sought to provide an objective method of diagnosis. There are several potential biomarkers, including Brain-Derived Neurotrophic Factor and various functional MRI techniques. One study developed a decision tree model of interpreting a series of fMRI scans taken during various activities. In their subjects, the authors of that study were able to achieve a sensitivity of 80% and a specificity of 87%, corresponding to a negative predictive value of 98% and a positive predictive value of 32% (positive and negative likelihood ratios were 6.15, 0.23, respectively). However, much more research is needed before these tests could be used clinically.

The following are the revised criteria for a diagnosis of cyclothymic disorder (DSM-IV-TR 301.13) from the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-IV-TR):

- A. For at least 2 years (1 year in children and adolescents), the presence of numerous periods with hypomanic symptoms and numerous periods with depressive symptoms that do not meet criteria for a Major Depressive Episode

- B. During the above period, the person has not been without the symptoms in A for more than 2 months in the 2-year period

- C. No Major Depressive Episode, Manic Episode, or Mixed Episode has been present during the first 2 years of the disturbance.

- D. The symptoms in Criterion A are not better accounted for by Schizoaffective Disorder and are not superimposed on Schizophrenia, Schizophreniform Disorder, Delusional Disorder, or Psychotic Disorder Not Otherwise Specified.

- E. The symptoms are not due to the direct physiological effects of a substance (e.g. drug of abuse, a medication) or a general medical condition (e.g., hyperthyroidism).

- F. The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

The DSM-IV-TR notes that the mood disturbance must be not severe enough to constitute a full-fledged manic or major depressive episode. The diagnosis requires that there be periods of both hypomania and depression and that periods of normal mood not last longer than 2 months.

The DSM-IV-TR also notes that Cyclothymia and borderline personality disorder share similar features and that individuals can be diagnosed with both BPD and Cyclothymia depending on the symptoms they present.

According to a substantial amount of epidemiology studies conducted, women are twice as likely to develop certain mood disorders, such as major depression. Although there is an equal number of men and women diagnosed with bipolar II disorder, women have a slightly higher frequency of the disorder.

In 2011, mood disorders were the most common reason for hospitalization among children aged 1–17 years in the United States, with approximately 112,000 stays. Mood disorders were top principal diagnosis for Medicaid super-utilizers in the United States in 2012. Further, a study of 18 States found that mood disorders accounted for the highest number of hospital readmissions among Medicaid patients and the uninsured, with 41,600 Medicaid patients and 12,200 uninsured patients being readmitted within 30 days of their index stay—a readmission rate of 19.8 per 100 admissions and 12.7 per 100 admissions, respectively. In 2012, mood and other behavioral health disorders were the most common diagnoses for Medicaid-covered and uninsured hospital stays in the United States (6.1% of Medicaid stays and 5.2% of uninsured stays).

A study conducted in 1988 to 1994 amongst young American adults involved a selection of demographic and health characteristics. A population-based sample of 8,602 men and women ages 17–39 years participated. Lifetime prevalence were estimated based on six mood measures:

1. major depressive episode (MDE) 8.6%,

2. major depressive disorder with severity (MDE-s) 7.7%,

3. dysthymia 6.2%,

4. MDE-s with dysthymia 3.4%,

5. any bipolar disorder 1.6%, and

6. any mood disorder 11.5%.

Questionnaires and checklists such as the Beck Depression Inventory or the Children's Depression Inventory can be used by a mental health provider to help detect, and assess the severity of depression. The Seasonal Pattern Assessment Questionnaire can be used to screen for seasonal affective disorder. Semi structured interviews such as the Kiddie Schedule for Affective Disorders and Schizophrenia (KSADS) and the Structured Clinical Interview for DSM-IV (SCID) are used for diagnostic confirmation of depression.

In 2016, the United States Preventive Services Task Force (USPSTF) recommended screening in the adult populations with evidence that it increases the detection of people with depression and with proper treatment improves outcomes. They recommend screening in those between the age of 12 to 18 as well.

A Cochrane review from 2005 found screening programs do not significantly improve detection rates, treatment, or outcome.

The "Diagnostic and Statistical Manual of Mental Disorders IV" (DSM-IV), published by the American Psychiatric Association, characterizes dysthymic disorder. The essential symptom involves the individual feeling depressed for the majority of days, and parts of the day, for at least two years. Low energy, disturbances in sleep or in appetite, and low self-esteem typically contribute to the clinical picture as well. Sufferers have often experienced dysthymia for many years before it is diagnosed. People around them often describe the sufferer in words similar to "just a moody person". Note the following diagnostic criteria:

1. During a majority of days for two years or more, the adult patient reports depressed mood, or appears depressed to others for most of the day.

2. When depressed, the patient has two or more of:

1. decreased or increased appetite

2. decreased or increased sleep (insomnia or hypersomnia)

3. Fatigue or low energy

4. Reduced self-esteem

5. Decreased concentration or problems making decisions

6. Feelings of hopelessness or pessimism

3. During this two-year period, the above symptoms are never absent longer than two consecutive months.

4. During the duration of the two-year period, the patient may have had a perpetual major depressive episode.

5. The patient has not had any manic, hypomanic, or mixed episodes.

6. The patient has never fulfilled criteria for cyclothymic disorder.

7. The depression does not exist only as part of a chronic psychosis (such as schizophrenia or delusional disorder).

8. The symptoms are often not directly caused by a medical illness or by substances, including drug abuse or other medications.

9. The symptoms may cause significant problems or distress in social, work, academic, or other major areas of life functioning.

In children and adolescents, mood can be irritable, and duration must be at least one year, in contrast to two years needed for diagnosis in adults.

Early onset (diagnosis before age 21) is associated with more frequent relapses, psychiatric hospitalizations, and more co-occurring conditions. For younger adults with dysthymia, there is a higher co-occurrence in personality abnormalities and the symptoms are likely chronic. However, in older adults suffering from dysthymia, the psychological symptoms are associated with medical conditions and/or stressful life events and losses.

Dysthymia can be contrasted with major depressive disorder by assessing the acute nature of the symptoms. Dysthymia is far more chronic (long lasting) than major depressive disorder, in which symptoms may be present for as little as 2 weeks. Also Dysthymia often presents itself at an earlier age than Major Depressive Disorder.

From the :

F33 Recurrent depressive disorder

- G1.There has been at least one previous episode, mild (F32.0), moderate (F32.1), or severe (F32.2 or F32.3), lasting a minimum of 2 weeks and separated from the current episode by at least 2 months free from any significant mood symptoms.

- G2. At no time in the past has there been an episode meeting the criteria or hypomanic or manic episode (F30.-).

- G3. Most commonly used exclusion criteria: the episode is not attributable to psychoactive substance use (F1) or any organic mental disorder, in the sense of F0. It is recommended to specify the predominant type of previous episodes (mild, moderate, severe, uncertain).

F33.0 Recurrent depressive disorder, current episode mild

- A. The general criteria for recurrent depressive disorder (F33) are met.

- B. The current episode meets the criteria for depressive episode, mild severity (F32.0).

- A fifth character may be used to specify the presence of the somatic syndrome, as defined in F32, in the current episode:

- F33.00 without somatic syndrome

- F33.01 with somatic syndrome

F33.1 Recurrent depressive disorder, current episode moderate

- A. The general criteria for recurrent depressive disorders (F33) are met.

- B. The current episode meets the criteria for depressive episode, moderate severity (F32.1).

- A fifth character may be used to specify the presence of the somatic syndrome, as defined in F32, in the current episode:

F33.10 without somatic syndrome

F33.11 with somatic syndrome

F33.2 Recurrent depressive disorder, current episode severe without psychotic symptoms

- A. The general criteria for recurrent depressive disorders (F33) are met.

- B. The current episode meets the criteria for severe depressive episode without psychotic symptoms (F32.2).

F33.3 Recurrent depressive disorder, current episode severe with psychotic symptoms

- A. The general criteria for recurrent depressive disorders (F33) are met.

- B. The current episode meets the criteria for severe depressive episode with psychotic symptoms (F32.3). A fifth character may be used to specify whether the psychotic symptoms are congruent or incongruent with the mood:

F33.30 with mood congruent psychotic symptoms

F33.31 with mood incongruent psychotic symptoms

F33.4 Recurrent depressive disorder, currently in remission

- A. The general criteria for recurrent depressive disorder (F33) have been met in the past.

- B. The current state does not meet the criteria for a depressive episode (F32.-) of any severity, or for any other disorder in F3 (the patient may receive treatment to reduce the risk of further episodes).

F33.8 Other recurrent depressive disorders

F33.9 Recurrent depressive disorder, unspecified

Healthcare providers may screen patients for depression using a screening tool, such as the Patient Healthcare Questionnaire-2 (PHQ-2).

To diagnose a major depressive episode, a trained healthcare provider must make sure that:

- The symptoms do not meet the criteria for a mixed episode.

- The symptoms must cause considerable distress or impair functioning at work, in social settings or in other important areas in order to qualify as an episode.

- The symptoms are not due to the direct physiological effects of a substance (e.g., abuse of a drug or medication) or a general medical condition (e.g., hypothyroidism).

- Other than in the case of severe symptoms (severely impaired functioning, severe preoccupation with worthlessness, ideas of suicide, delusions or hallucinations or psychomotor retardation).

The DSM-5, released in May 2013, separates the mood disorder chapter from the DSM-TR-IV into two sections: Depressive and Related Disorders and Bipolar and Related Disorders. Bipolar Disorders falls in between Depressive Disorders and Schizophrenia Spectrum and Related Disorders “in recognition of their place as a bridge between the two diagnostic classes in terms of symptomatology, family history and genetics” (Ref. 1, p 123). Bipolar Disorders underwent a few changes in the DSM-5, most notably the addition of more specific symptomology related to hypomanic and mixed manic states. Depressive Disorders underwent the most changes, the addition of three new disorders: disruptive mood dysregulation disorder, persistent depressive disorder (previously dysthymia), and premenstrual dysphoric disorder (previously in Appendix B, the section for disorders needing further research). Disruptive mood dysregulation disorder is meant as a diagnosis for children and adolescents who would normally be diagnosed with bipolar disorder as a way to limit the bipolar diagnosis in this age cohort. Major depressive disorder (MDD) also underwent a notable change, in that the bereavement clause has been removed. Those previously exempt from a diagnosis of MDD due to bereavement are now candidates for the MDD diagnosis.

Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances. The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases.

Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.

Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations. It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries.

More structured approaches are being increasingly used to measure levels of mental illness.

- HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts. In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity. Research has been supportive of HoNOS, although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.

The past DSM-IV criteria for IED were similar to the current criteria, however verbal aggression was not considered as part of the diagnostic criteria. The DSM-IV diagnosis was characterized by the occurrence of discrete episodes of failure to resist aggressive impulses that result in violent assault or destruction of property. Additionally, the degree of aggressiveness expressed during an episode should be grossly disproportionate to provocation or precipitating psychosocial stressor, and, as previously stated, diagnosis is made when certain other mental disorders have been ruled out, e.g., a head injury, Alzheimer's disease, etc., or due to substance abuse or medication. Diagnosis is made using a psychiatric interview to affective and behavioral symptoms to the criteria listed in the DSM-IV.

The DSM-IV-TR was very specific in its definition of Intermittent Explosive Disorder which was defined, essentially, by exclusion of other conditions. The diagnosis required:

1. several episodes of impulsive behavior that result in serious damage to either persons or property, wherein

2. the degree of the aggressiveness is grossly disproportionate to the circumstances or provocation, and

3. the episodic violence cannot be better accounted for by another mental or physical medical condition.

Affective disorders in patients with MD can only be detected by means of a clinician-administered diagnostic interview. Organic exclusion rules and other criteria are used in making the diagnosis of MD.

According to the American Psychiatric Association DSM-IV criteria, Seasonal Affective Disorder is not regarded as a separate disorder. It is called a "course specifier" and may be applied as an added description to the pattern of major depressive episodes in patients with major depressive disorder or patients with bipolar disorder.

The "Seasonal Pattern Specifier" must meet four criteria: depressive episodes at a particular time of the year; remissions or mania/hypomania at a characteristic time of year; these patterns must have lasted two years with no nonseasonal major depressive episodes during that same period; and these seasonal depressive episodes outnumber other depressive episodes throughout the patient's lifetime. The Mayo Clinic describes three types of SAD, each with its own set of symptoms.

311- Depressive Disorder Not Otherwise Specified (NOS)

The Depressive disorder NOS category includes disorders with depressive features that do not meet the criteria for Major Depressive Disorder, Dysthymic disorder, Adjustment Disorder with Depressed Mood or Adjustment Disorder with Mixed Anxiety and Depressed Mood. Sometimes depressive symptoms can present as part of an Anxiety Disorder Not otherwise Specified. Examples of Depressive Disorder Not Otherwise Specified include.

- Premenstrual Dysphoric Disorder: in most menstrual cycles during the past years, (e.g., markedly depressed mood, marked anxiety, marked affective lability, or decreased interest in activities) regularly occurred during the onset of menses. These symptoms must be severe enough to markedly interfere with work, school, or usual activities and be entirely absent for at least 1 week post menses.

- Minor depressive disorder: episodes of at least 2 weeks of depressive symptoms but with fewer than the five items required for Major Depressive Disorder.

- Recurrent brief depressive disorder: depressive episodes lasting from 2 days up to 2 weeks, occurring at least once a month for 12 months (not associated with the menstrual cycle)

- Post psychotic depressive Disorder of schizophrenia: a Major Depressive Episode that occurs during the residual phase of schizophrenia.

- A Major Depressive Episode superimposed on delusional disorder, Psychotic Disorder Not Otherwise Specified, or the active phase of schizophrenia.

- Situations in which the clinician has concluded that a depressive disorder is present but is unable to determine whether it is primary, due to a general medical condition, or substance induced.

Symptoms of the disorder may arise due to several reasons. These include:

- Distress due to medical conditions

- Environmental effects and situations

Treatment of minor depressive disorder has not been studied as extensively as major depressive disorder. Although there are often similarities in the treatments used, there are also differences in what may work better for the treatment of minor depressive disorder. Some third-party payers do not pay to cover treatment for minor depressive disorder.

The leading treatment techniques for minor depressive disorder are the use of antidepressants and therapy. Typically, patients with minor depression were treated by watchful waiting, prescribed antidepressants, and given brief supportive counseling, but Problem-Solving Treatment for Primary Care (PST-PC) is a Cognitive-Behavioral Therapy that has gained popularity. In one study, Problem-Solving Treatment for Primary Care (PST-PC) and Paroxetine, an antidepressant, were shown to be equally effective in significantly reducing symptoms. In another study, PST-PC was compared with the more typical care of the time and shown to reduce symptoms more quickly. Although the use of antidepressants has been widely used, not all agree that it is an appropriate treatment for some minor depression disorder settings.

Another alternative that has been researched is the use of St. John's wort ("Hypericum perforatum"). This herbal treatment has been studied by various groups with various results. Some studies show evidence of the treatment being helpful to treat minor depression, but others show that it does no better than the placebo.

Many psychiatric disorders and some substance use disorders are associated with increased aggression and are frequently comorbid with IED, often making differential diagnosis difficult. Individuals with IED are, on average, four times more likely to develop depressive or anxiety disorders, and three times more likely to develop substance use disorders.

Bipolar disorder has been linked to increased agitation and aggressive behavior in some individuals, but for these individuals aggressiveness is limited to manic and/or depressive episodes, whereas individuals with IED experience aggressive behavior even during periods with a neutral or positive mood. In one clinical study, the two disorders co-occurred 60% of the time. Patients report manic-like symptoms occurring just before outbursts and continuing throughout. According to a study, the average onset age of IED was around five years earlier than the onset age of bipolar disorder, indicating a possible correlation between the two.

Similarly, alcohol and other substance use disorders may exhibit increased aggressiveness, but unless this aggression is experienced outside of periods of acute intoxication and withdrawal, no diagnosis of IED is given. For chronic disorders, such as PTSD, it is important to assess whether the level of aggression met IED criteria prior to the development of another disorder. In antisocial personality disorder, interpersonal aggression is usually instrumental in nature (i.e., motivated by tangible rewards), whereas IED is more of an impulsive, unpremeditated reaction to situational stress.

The person may have repeated thoughts about death (other than the fear of dying) or suicide (with or without a plan), or may have made a suicide attempt. The frequency and intensity of thoughts about suicide can range from believing that friends and family would be better off if one were dead, to frequent thoughts about committing suicide (generally related to wishing to stop the emotional pain), to detailed plans about how the suicide would be carried out. Those who are more severely suicidal may have made specific plans and decided upon a day and location for the suicide attempt.

Both psychotherapy as well as different drugs (e.g. serotonin reuptake inhibitors - SSRIs or mood stabilizers, e.g. lithium, antiepileptics) have been suggested as treatments. However, no randomized controlled treatment trial of RBD has been conducted.