Measurement of urine for the ratio of trimethylamine to trimethylamine oxide is the standard screening test. A blood test is available to provide genetic analysis. The prominent enzyme responsible for TMA N-oxygenation is coded by the "FMO3" gene.

False positives can occur in the following conditions, where elevated TMA can be present in the urine without any underlying TMAU:

- Urinary tract infection

- Bacterial vaginosis

- Cervical cancer

- Advanced liver or kidney disease

A similar foul-smelling odor of the urine has also been associated with colonization of the urinary tract with a bacterium called "Aerococcus urinae", especially in children.

Detection of the disorder is possible with an organic acid analysis of the urine. Patients with SSADH deficiency will excrete high levels of GHB but this can be difficult to measure since GHB has high volatility and may be obscured on gas chromatography or mass spectrometry studies by a high urea peak. Other GABA metabolites can also be identified in urine such as glycine. Finally, succinic semialdehyde dehydrogenase levels can be measured in cultured leukocytes of the patient. This occurs due to the accumulation of 4,5-dihydroxyhexanoic acid which is normally undetectable in mammalian tissues but is characteristic of SSADH deficiency. This agent can eventually compromise the pathways of fatty acid, glycine, and pyruvate metabolism, and then become detectable in patients' leukocytes. Such enzyme levels can also be compared to non-affected parents and siblings.

There is no known cure or treatment for the disorder.

The metabolic and clinical manifestations of TMAU are generally regarded as benign, as there is no associated organ dysfunction. This

designation, and the fact that the condition is often unrecognised by doctors, can have important ramifications including missed or delayed diagnosis.

Affected individuals experience shame and embarrassment, fail to maintain relationships, avoid contact with people who comment on their condition, and are obsessive about masking the odour with hygiene products and even smoking. The malodorous aspect can have serious and destructive effects on schooling, personal life, career and relationships, resulting in social isolation, low self-esteem, depression, paranoid behaviour, and suicide. Delayed diagnosis, body odour and the lack of cure may lead to psychosocial issues. When the condition is suspected or known to occur in a family, genetic testing can be helpful in identifying the specific individuals who have or carry the disorder.

Ways of reducing the fishy odor may include:

- Avoiding foods such as egg yolks, legumes, red meats, fish, beans and other foods that contain choline, carnitine, nitrogen, sulfur and lecithin

- Taking low doses of antibiotics such as neomycin and metronidazole in order to reduce the amount of bacteria in the gut

- Using slightly acidic detergent with a pH between 5.5 and 6.5

Additionally, at least one study has suggested that daily intake of the supplements activated charcoal and copper chlorophyllin may improve the quality of life of individuals afflicted with TMAU by helping their bodies to oxidize and convert TMA to the odorless "N"-oxide (TMAO) metabolite. Study participants experienced subjective reduction in odor as well as objective reduction in TMA and increase in TMAO concentration measured in their urine. The study found that:

- 85% of test participants experienced complete loss of detectable "fishy" odor

- 10% experienced some reduction in detectable odor

- 5% did not experience any detectable odor reduction

Certain diagnostic tools can also be used to help determine the extent of dysgeusia. Electrophysiological tests and simple reflex tests may be applied to identify abnormalities in the nerve-to-brainstem pathways. For example, the blink reflex may be used to evaluate the integrity of the trigeminal nerve–pontine brainstem–facial nerve pathway, which may play a role in gustatory function.

Structural imaging is routinely used to investigate lesions in the taste pathway. Magnetic resonance imaging allows direct visualization of the cranial nerves. Furthermore, it provides significant information about the type and cause of a lesion. Analysis of mucosal blood flow in the oral cavity in combination with the assessment of autonomous cardiovascular factors appears to be useful in the diagnosis of autonomic nervous system disorders in burning mouth syndrome and in patients with inborn disorders, both of which are associated with gustatory dysfunction. Cell cultures may also be used when fungal or bacterial infections are suspected.

In addition, the analysis of saliva should be performed, as it constitutes the environment of taste receptors, including transport of tastes to the receptor and protection of the taste receptor. Typical clinical investigations involve sialometry and sialochemistry. Studies have shown that electron micrographs of taste receptors obtained from saliva samples indicate pathological changes in the taste buds of patients with dysgeusia and other gustatory disorders.

PKU is commonly included in the newborn screening panel of many countries, with varied detection techniques. Most babies in developed countries are screened for PKU soon after birth. Screening for PKU is done with bacterial inhibition assay (Guthrie test), immunoassays using fluorometric or photometric detection, or amino acid measurement using tandem mass spectrometry (MS/MS). Measurements done using MS/MS determine the concentration of Phe and the ratio of Phe to tyrosine, the ratio will be elevated in PKU.

In order to further classify the extent of dysgeusia and clinically measure the sense of taste, gustatory testing may be performed. Gustatory testing is performed either as a whole-mouth procedure or as a regional test. In both techniques, natural or electrical stimuli can be used. In regional testing, 20 to 50 µL of liquid stimulus is presented to the anterior and posterior tongue using a pipette, soaked filter-paper disks, or cotton swabs. In whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient is asked to swish the solution around in the mouth.

Threshold tests for sucrose (sweet), citric acid (sour), sodium chloride (salty), and quinine or caffeine (bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test." In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water. Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row.

Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour). Direct scaling cannot be used to determine if a taste stimulus is being perceived at abnormal levels. In this case, magnitude matching is used, in which a patient is asked to rate the intensities of taste stimuli and stimuli of another sensory system, such as the loudness of a tone, on a similar scale. For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones. Assuming normal hearing, the results of this cross-sensory test show the relative strength of the sense of taste in relation to the loudness of the auditory stimulus. Although many of the tests are based on ratings using the direct scaling method, some tests do use the magnitude-matching procedure.

Other tests include identification or discrimination of common taste substances. Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily. In addition to techniques based on the administration of chemicals to the tongue, electrogustometry is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical direct current. Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue. Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.

For women with phenylketonuria, it is important for the health of their children to maintain low Phe levels before and during pregnancy. Though the developing fetus may only be a carrier of the PKU gene, the intrauterine environment can have very high levels of phenylalanine, which can cross the placenta. The child may develop congenital heart disease, growth retardation, microcephaly and intellectual disability as a result. PKU-affected women themselves are not at risk of additional complications during pregnancy.

In most countries, women with PKU who wish to have children are advised to lower their blood Phe levels (typically to between 2 and 6 mg/dL) before they become pregnant, and carefully control their levels throughout the pregnancy. This is achieved by performing regular blood tests and adhering very strictly to a diet, in general monitored on a day-to-day basis by a specialist metabolic dietitian. In many cases, as the fetus' liver begins to develop and produce PAH normally, the mother's blood Phe levels will drop, requiring an increased intake to remain within the safe range of 2–6 mg/dL. The mother's daily Phe intake may double or even triple by the end of the pregnancy, as a result. When maternal blood Phe levels fall below 2 mg/dL, anecdotal reports indicate that the mothers may suffer adverse effects, including headaches, nausea, hair loss, and general malaise. When low phenylalanine levels are maintained for the duration of pregnancy, there are no elevated levels of risk of birth defects compared with a baby born to a non-PKU mother.

Cranial computed topography, magnetic resonance imaging, and flurodeoxyglucose positron emission topography are just some of the neuroimaging modalities that have been used to diagnose patients with SSADH deficiency. On the basis of 29 previously published cases that had imaging results available, there were some common abnormalities found. These included increased T2-weighted signal abnormalities involving the globus pallidi bilaterally and symmetrically as well as the presence of subcortical white matter. Similar abnormalities have been identified in the brainstem and cerebellar dentate nucleus.

Signal intensity on a T2 image may be a result of edema or an inflammatory response. Because this type of imaging is a water detecting sequence, any form of calcification or mineralization would also appear dark, thus explaining why accumulation of extra blood or fluid would appear bright on a T2 image. Another explanation for signal intensity may be demyelination since the globus pallidi are traversed by a number of myelinated axons, thus confirming Ren and Mody’s 2003 work proving that repeated exposure of GHB to MAP kinase affected myelin expression, thus causing the numerous neurological dysfunctions seen in SSADH deficiency patients. Ultimately, because the globus pallidus is intimately linked with the basal ganglia and thalamus, it would be expected that some of the motor dysfunctions seen in SSADH patients such as ataxia and hyporeflexia would be common.

One of, if not the most common form of organic acidemia, methylmalonic acidemia is not apparent at birth as symptoms usually do not present themselves until proteins are added to the infant's diet. Because of this, symptoms typically manifest anytime within the first year of life. Due to the severity and rapidity in which this disorder can cause complications when left undiagnosed, screening for methylmalonic acidemia is often included in the newborn screening exam.

Because of the inability to properly break down amino acids completely, the byproduct of protein digestion, the compound methylmalonic acid, is found in a disproportionate concentration in the blood and urine of those afflicted. These abnormal levels are used as the main diagnostic criteria for diagnosing the disorder. This disorder is typically determined through the use of a urine analysis or blood panel. The presence of methylmalonic acidemia can also be suspected through the use of a CT or MRI scan or ammonia test, however these tests are by no means specific and require clinical and metabolic/correlation. Elevated levels of ammonia, glycine, and ketone bodies may also be present in the blood and urine.

Methylmalonic acidemia has varying diagnoses, treatment requirements and prognoses, which are determined by the specific genetic mutation causing the inherited form of the disorder. The following are the known genotypes responsible for methylmalonic acidemia:

The mut type can further be divided in mut0 and mut- subtypes, with mut0 characterized by a complete lack of methylmalonyl CoA mutase and more severe symptoms and mut- characterized by a decreased amount of mutase activity.

Mut-, cblB, and cblA versions of methylmalonic acidemia have been found to be cobalamin responsive. Mut0 is a nonresponsive variant.

Due to its non-specific nature, diagnosing CSE requires a multidisciplinary "Solvent Team" typically consisting of a neurologist, occupational physician, occupational hygienist, neuropsychologist, and sometimes a psychiatrist or toxicologist. Together, the team of specialists together assesses the patient's history of exposure, symptoms, and course of symptom development relative to the amount and duration of exposure, presence of neurological signs, and any existing neuropsychological impairment.

Furthermore, CSE must be diagnosed "by exclusion". This means that all other possible causes of the patient’s symptoms must first be ruled out beforehand. Because screening and assessing for CSE is a complex and time-consuming procedure requiring several specialists of multiple fields, few cases of CSE are formally diagnosed in the medical field. This may, in part, be a reason for the syndrome’s lack of recognition. The solvents responsible for neurological effects dissipate quickly after an exposure, leaving only indirect evidence of their presence, in the form of temporary or permanent impairments.

Brain imaging techniques that have been explored in research have shown little promise as alternative methods to diagnose CSE. Neuroradiology and functional imaging have shown mild cortical atrophy, and effects in dopamine-mediated frontostriatal circuits in some cases. Examinations of regional cerebral blood flow in some imaging techniques have also shown some cerebrovascular abnormalities in patients with CSE, but the data were not different enough from healthy patients to be considered significant. The most promising brain imaging technique being studied currently is functional magnetic resonance imaging (fMRI) but as of now, no specific brain imaging techniques are available to reliably diagnose CSE.

Introduced by a working group from the World Health Organization (WHO) in 1985, WHO diagnostic criteria states that CSE can occur in three stages, organic affective syndrome (type I), mild chronic toxic encephalopathy (type II), and severe chronic toxic encephalopathy (type III). Shortly after, a workshop in Raleigh-Durham, NC (United States) released a second diagnostic criterion which recognizes four stages as symptoms only (type 1), sustained personality or mood swings (type 2A), impairment of intellectual function (type 2B), and dementia (type 3). Though not identical, the WHO and Raleigh criteria are relatively comparable. WHO type I and Raleigh types 1 and 2A are believed to encompass the same stages of CSE, and WHO type II and Raleigh type 2B both involve deficiencies in memory and attention. No other international classifications for CSE have been proposed, and neither the WHO nor Raleigh criteria have been uniformly accepted for epidemiological studies.

To treat people with a deficiency of this enzyme, they must avoid needing gluconeogenesis to make glucose. This can be accomplished by not fasting for long periods, and eating high-carbohydrate food. They should avoid fructose containing foods (as well as sucrose which breaks down to fructose).

As with all single-gene metabolic disorders, there is always hope for genetic therapy, inserting a healthy copy of the gene into existing liver cells.

While frustrating, the ultimate outcome is very good: symptoms typically disappear in about four years.

When untreated, the prognosis for ORS is generally poor. It is chronic, lasting many years or even decades with worsening of symptoms rather than spontaneous remission. Transformation to another psychiatric condition is unlikely, although very rarely what appears to be ORS may later manifest into schizophrenia, psychosis, mania, or major depressive disorder. The most significant risk is suicide.

When treated, the prognosis is better. In one review, the proportion of treated ORS cases which reported various outcomes were assessed. On average, the patients were followed for 21 months (range: 2 weeks to 10 years). With treatment, 30% recovered (i.e. no longer experienced ORS odor beliefs and thoughts of reference), 37% improved and in 33% there was a deterioration in the condition (including suicide) or no change from the pre-treatment status.

A wide variety of companies manufacture ketone screening strips. A strip consists of a thin piece of plastic film slightly larger than a matchstick, with a reagent pad on one end that is either dipped into a urine sample or passed through the stream while the user is voiding. The pad is allowed to react for an exact, specified amount of time (it is recommended to use a stopwatch to time this exactly and disregard any resultant colour change after the specified time); its resulting colour is then compared to a graded shade chart indicating a detection range from negative presence of ketones up to a significant quantity. It is worth noting that in severe diabetic ketoacidosis, the dipstix reaction based on sodium nitroprusside may underestimate the level of ketone bodies in the blood. It is sensitive to acetoacetate only, and the ratio of beta-hydroxybutyrate to acetoacetate is shifted from a normal value of around 1:1 up to around 10:1 under severely ketoacetotic conditions, due to a changing redox milieu in the liver. Measuring acetoacetate alone will thus underestimate the accompanying beta-hydroxybutyrate if the standard conversion factor is applied.

Hangovers are poorly understood from a medical point of view. Health care professionals prefer to study alcohol abuse from a standpoint of treatment and prevention, and there is a view that the hangover provides a useful, natural and intrinsic disincentive to excessive drinking.

Within the limited amount of serious study on the subject, there is debate about whether a hangover may be prevented or at least mitigated. There is also a vast body of folk medicine and simple quackery. A four-page literature review in the "British Medical Journal" concludes: "No compelling evidence exists to suggest that any conventional or complementary intervention is effective for preventing or treating alcohol hangover. The most effective way to avoid the symptoms of alcohol induced hangover is to avoid drinking." Most remedies do not significantly reduce overall hangover severity. Some compounds reduce specific symptoms such as vomiting and headache, but are not effective in reducing other common hangover symptoms such as drowsiness and fatigue

PCCI affects a subset of cancer survivors, though the overall epidemiology and prevalence is not well known and may depend on many factors.

It generally affects about 10–40% of breast cancer patients, with higher rates among pre-menopausal women and patients who receive high-dose chemotherapy.

Treatment or management of organic acidemias vary; eg see methylmalonic acidemia, propionic acidemia, isovaleric acidemia, and maple syrup urine disease.

As of 1984 there were no effective treatments for all of the conditions, though treatment for some included a limited protein/high carbohydrate diet, intravenous fluids, amino acid substitution, vitamin supplementation, carnitine, induced anabolism, and in some cases, tube-feeding.

As of 1993 ketothiolase deficiency and other OAs were managed by trying to restore biochemical and physiologic homeostasis; common therapies included restricting diet to avoid the precursor amino acids and use of compounds to either dispose of toxic metabolites or increase enzyme activity.

There is no evidence that any treatment for hangovers is very effective.

- Rehydration: Drinking water before going to bed or during hangover may relieve dehydration-associated symptoms such as thirst, dizziness, dry mouth, and headache.

- Non-steroidal anti-inflammatory drugs such as aspirin or ibuprofen have been proposed as a treatment for the headaches associated with a hangover. There however is no evidence to support a benefit, and there are concerns that taking alcohol and aspirin together may increase the risk of stomach bleeding and liver damage.

- Tolfenamic acid, an inhibitor of prostaglandin synthesis, in a 1983 study reduced headache, nausea, vomiting, irritation but had no effect on tiredness in 30 people.

- Pyritinol: A 1973 study found that large doses (several hundred times the recommended daily intake) of Pyritinol, a synthetic Vitamin B6 analog, can help to reduce hangover symptoms. Possible side effects of pyritinol include hepatitis (liver damage) due to cholestasis and acute pancreatitis.

- Yeast-based extracts: The difference in the change for discomfort, restlessness, and impatience were statistically significant but no significant differences on blood chemistry parameters, blood alcohol or acetaldehyde concentrations have been found, and it did not significantly improve general well-being.

Normal olfactory acuity will usually return over time if the cause is environmental, even if it is untreated. The hyperosmic person may need to be removed from strong odorants for a period of time if the sensation becomes unbearable. Before they had been discontinued due to undesirable side effects, butyrophenones or thioridazine hydrochloride, both of which are dopamine antagonists, have been used to treat hyperosmia.

Organic acidemias are usually diagnosed in infancy, characterized by urinary excretion of abnormal amounts or types of organic acids. The diagnosis is usually made by detecting an abnormal pattern of organic acids in a urine sample by gas chromatography-mass spectrometry. In some conditions, the urine is always abnormal, in others the characteristic substances are only present intermittently. Many of the organic acidemias are detectable by newborn screening with tandem mass spectrometry.

These disorders vary in their prognosis, from manageable to fatal, and usually affect more than one organ system, especially the central nervous system.

Neurological damage and developmental delay are common factors in diagnosis, with associated symptoms ranging from poor feeding to slow growth, lethargy, vomiting,

dehydration, malnutrition, hypoglycemia, hypotonia, metabolic acidosis, ketoacidosis, hyperammonemia, and if left untreated, death.

Fortunately for patients afflicted with parosmia, symptoms usually decrease with time. Although there are instances of parosmia affecting patients for years at a time, this is certainly not the majority of cases. There have been experiments done to treat parosmia with L-Dopa, but besides that there are no current treatments other than inducing anosmia or hyposmia to the point where the odors are negligible.

The most challenging task for the examiner is to determine and obtain the correct symptoms and associate them with one of the olfactory disorders, as there are several of them and they are related to each other.

The first step the examiner usually takes is to investigate if the problem is olfactory or gustatory related. As it may be that the patient releases certain bodily odors that are causing them to have this perception.

If the examiner is able to confirm that the problem is olfactory related, the next step is to determine which olfactory disorder the patient suffers from. The following is a list of possible olfactory disorders:

- anosmia

- dysosmia

- hyperosmia

- hyposmia

- parosmia or troposmia

- phantosmia

The second step is very difficult for both the examiner and the patient as the patient has some difficulty describing their perception of the phantom odor. Furthermore, the patient is in a position of stress and anxiety thus it is crucial that the examiner be patient.

After determining the nature of the disorder, and confirming phantosmia, the examiner must then have the patient describe their perception of the phantom odor. In many cases, patients have described the odor to be that of something burning and rotten and have described it to be unpleasant and foul.

The third step for the examiner is to determine the health history of the patient to take note of head trauma, accidents, upper respiratory infections, allergic rhinitis or chronic rhinitis. Although these may be events that have resulted in the phantom odor, studies conducted by Zilstrof have found that the majority of phantosmia patients have no previous history of head trauma and upper respiratory infections.

Diagnosing a patient can be difficult as they are often frustrated from ineffective therapy and being told they have mental illnesses. Some patients actually have trouble deciding whether they have a taste or smell problem. In this case asking questions about food choices will help determine whether a patient has a smell or taste disorder. It is important to identify whether the distortion applies to an inhaled odorant or if an odor exists without the stimulus. The distortion of an odorant is presented in two types: the stimuli are different from what one remembers and in the second, everything has a similar smell. A clinical history can also help determine what kind of disorder one has because events such as respiratory infection and head trauma are usually indications of parosmia where as phantosmias usually have no history of such events and occur spontaneously. Unfortunately there are no accurate diagnostic tests or methods for dysosmia. Evaluation must be done through questionnaires and medical history.