Diagnosis of autoimmune disorders largely rests on accurate history and physical examination of the patient, and high index of suspicion against a backdrop of certain abnormalities in routine laboratory tests (example, elevated C-reactive protein). In several systemic disorders, serological assays which can detect specific autoantibodies can be employed. Localised disorders are best diagnosed by immunofluorescence of biopsy specimens. Autoantibodies are used to diagnose many autoimmune diseases. The levels of autoantibodies are measured to determine the progress of the disease.

There is no official diagnostic criteria for UCTD. Diagnostic testing generally aims to determine whether a patient has a "definite" or "undifferentiated" connective tissue disease.

Most patients will maintain a diagnosis of undifferentiated connective tissue disease. However, about one third of UCTD patients will differentiate to a specific autoimmune disease, like rheumatoid arthritis or systemic sclerosis. About 12 percent of patients will go into remission.

Severe vitamin D deficiency has been associated with the progression of UCTD into defined connective tissue diseases. The presence of the autoantibodies anti-dsDNA, anti-Sm, and anti-cardiolipin has been shown to correlate with the development of systemic lupus erythematosus, specifically.

A growing body of evidence supports that prevention is effective in reducing the effect of chronic conditions; in particular, early detection results in less severe outcomes. Clinical preventive services include screening for the existence of the disease or predisposition to its development, counseling and immunizations against infectious agents. Despite their effectiveness, the utilization of preventive services is typically lower than for regular medical services. In contrast to their apparent cost in time and money, the benefits of preventive services are not directly perceived by patient because their effects are on the long term or might be greater for society as a whole than at the individual level.

Therefore, public health programs are important in educating the public, and promoting healthy lifestyles and awareness about chronic diseases. While those programs can benefit from funding at different levels (state, federal, private) their implementation is mostly in charge of local agencies and community-based organizations.

Studies have shown that public health programs are effective in reducing mortality rates associated to cardiovascular disease, diabetes and cancer, but the results are somewhat heterogeneous depending on the type of condition and the type of programs involved. For example, results from different approaches in cancer prevention and screening depended highly on the type of cancer.

The rising number of patient with chronic diseases has renewed the interest in prevention and its potential role in helping control costs. In 2008, the Trust for America's Health produced a report that estimated investing $10 per person annually in community-based programs of proven effectiveness and promoting healthy lifestyle (increase in physical activity, healthier diet and preventing tobacco use) could save more than $16 billion annually within a period of just five years.

Infectious pathogen-associated diseases include many of the most common and costly chronic illnesses. The treatment of chronic diseases accounts for 75% of all US healthcare costs (amounting to $1.7 trillion in 2009).

Treatments for autoimmune disease have traditionally been immunosuppressive, anti-inflammatory, or palliative. Managing inflammation is critical in autoimmune diseases. Non-immunological therapies, such as hormone replacement in Hashimoto's thyroiditis or Type 1 diabetes mellitus treat outcomes of the autoaggressive response, thus these are palliative treatments. Dietary manipulation limits the severity of celiac disease. Steroidal or NSAID treatment limits inflammatory symptoms of many diseases. IVIG is used for CIDP and GBS. Specific immunomodulatory therapies, such as the TNFα antagonists (e.g. etanercept), the B cell depleting agent rituximab, the anti-IL-6 receptor tocilizumab and the costimulation blocker abatacept have been shown to be useful in treating RA. Some of these immunotherapies may be associated with increased risk of adverse effects, such as susceptibility to infection.

Helminthic therapy is an experimental approach that involves inoculation of the patient with specific parasitic intestinal nematodes (helminths). There are currently two closely related treatments available, inoculation with either Necator americanus, commonly known as hookworms, or Trichuris Suis Ova, commonly known as Pig Whipworm Eggs.

T cell vaccination is also being explored as a possible future therapy for autoimmune disorders.

A list of the more common and well-known diseases associated with infectious pathogens is provided and is not intended to be a complete listing.

By age 3 about 30% of rats have had cancer, whereas by age 85 about 30% of humans have had cancer. Humans, dogs and rabbits get Alzheimer's disease, but rodents do not. Elderly rodents typically die of cancer or kidney disease, but not of cardiovascular disease. In humans, the relative incidence of cancer increases exponentially with age for most cancers, but levels off or may even decline by age 60–75 (although colon/rectal cancer continues to increase).

People with the so-called segmental progerias are vulnerable to different sets of diseases. Those with Werner's syndrome suffer from osteoporosis, cataracts and cardiovascular disease, but not neurodegeneration or Alzheimer's disease; those with Down syndrome suffer type 2 diabetes and Alzheimer's disease, but not high blood pressure, osteoporosis or cataracts. In Bloom syndrome, those afflicted most often die of cancer.

Individuals found to have circulating cryoglobulins but no signs or symptoms of cryoglobulinemic diseases should be evaluated for the possibility that their cryoglobulinemia is a transient response to a recent or resolving infection. Those with a history of recent infection that also have a spontaneous and full resolution of their cryoglobulinemia need no further treatment. Individuals without a history of infection and not showing resolution of their cryoglobulinemia need to be further evaluated. Their cryoglobulins should be analyzed for their composition of immunoglobulin type(s) and complement component(s) and examined for the presence of the premalignant and malignant diseases associated with Type I disease as well as the infectious and autoimmune diseases associated with type II and type III disease. A study conducted in Italy on >140 asymptomatic individuals found five cases of hepatitis C-related and one case of hepatitis b-related cryoglobulinemia indicating that a complete clinical examination of asymptomatic individuals with cryoglobulinemia offers a means for finding people with serious but potentially treatable and even curable diseases. Individuals who show no evidence of a disease underlying their cryoglobulinemia and who remain asymptomatic should be followed closely for any changes that may indicate development of cryoglobulinemic disease.

While risk factors vary with age and gender, most of the common chronic diseases in the US are caused by dietary, lifestyle and metabolic risk factors that are also responsible for the resulting mortality. Therefore, these conditions might be prevented by behavioral changes, such as quitting smoking, adopting a healthy diet, and increasing physical activity. Social determinants are important risk factors for chronic diseases. Social factors, e.g., socioeconomic status, education level, and race/ethnicity, are a major cause for the disparities observed in the care of chronic disease. Lack of access and delay in receiving care result in worse outcomes for patients from minorities and underserved populations. Those barriers to medical care complicate patients monitoring and continuity in treatment.

In the US, Minorities and low-income populations are less likely to access and receive preventive services necessary to detect conditions at an early stage.

The majority of US health care and economic costs associated with medical conditions are for the costs of chronic diseases and conditions and associated health risk behaviors. Eighty-four percent of all health care spending in 2006 was for the 50% of the population who have one or more chronic medical conditions (CDC, 2014).

All patients with symptomatic cryoglobulinemia are advised to avoid, or protect their extremities, from exposure to cold temperatures. Refrigerators, freezers, and air-conditioning represent dangers of such exposure.

The diagnosis of the disease is mainly clinical (see diagnostic criteria). A laboratory workup is needed primarily to investigate for the presence of associated disorders (metabolic, autoimmune, and renal diseases).

- Every patient should have a fasting blood glucose and lipid profile, creatinine evaluation, and urinalysis for protein content at the first visit, after which he/she should have these tests on a regular basis.

- Although uncommon, lipid abnormalities can occur in the form of raised triglyceride levels and low high-density lipoprotein cholesterol levels.

- Patients usually have decreased serum C3 levels, normal levels of C1 and C4, and high levels of C3NeF (autoantibody), which may indicate the presence of renal involvement.

- Antinuclear antibodies (ANA) and antidouble-stranded deoxyribonucleic acid (DNA) antibodies have reportedly been observed in some patients with acquired partial lipodystrophy.

- A genetic workup should be performed if the familial form of lipodystrophy is suggested.

Laboratory work for associated diseases includes:

- Metabolic disease - fasting glucose, glucose tolerance test, lipid profile, and fasting insulin to characterize the insulin resistance state; free testosterone (in women) to look for polycystic ovary syndrome.

- Autoimmune disease - ANA, antidouble-stranded DNA, rheumatoid factor, thyroid antibodies, C3, and C3NeF.

As a confirmatory test, whole-body MRI usually clearly demonstrates the extent of lipodystrophy. MRI is not recommended on a routine basis.

For those patients with periodontitis as a manifestation of hematologic disorders, coordination with the patient's physician is instrumental in planning periodontal treatment. Therapy should be avoided during periods of exacerbation of the malignancy or during active phases of chemotherapy, and antimicrobial therapy might be considered when urgent treatment must be performed when granulocyte counts are low.

Mitochondrial diseases are usually detected by analysing muscle samples, where the presence of these organelles is higher. The most common tests for the detection of these diseases are:

1. Southern blot to detect big deletions or duplications

2. PCR and specific mutation analysis

3. Sequencing

Aging (senescence) increases vulnerability to age-associated diseases, whereas genetics determines vulnerability or resistance between species and individuals within species. Some age-related changes (like graying hair) are said to be unrelated to an increase in mortality. But some biogerontologists believe that the same underlying changes that cause graying hair also increase mortality in other organ systems and that understanding the incidence of age-associated disease will advance knowledge of the biology of senescence just as knowledge of childhood diseases advanced knowledge of human development.

Strategies for Engineered Negligible Senescence (SENS) is a research strategy which aims to repair a few "root causes" for age-related illness and degeneration, as well as develop medical procedures to periodically repair all such damage in the human body, thereby maintaining a youth-like state indefinitely. So far, the SENS programme has identified seven types of aging-related damage, and feasible solutions have been outlined for each. However, critics argue that the SENS agenda is optimistic at best, and that the aging process is too complex and little-understood for SENS to be scientific or implementable in the foreseeable future.

In 1993, Peter James Dyck divided HSAN I further into five subtypes HSAN IA-E based on the presence of additional features. These features were thought to result from the genetic diversity of HSAN I (i.e. the expression of different genes, different alleles of a single gene, or modifying genes) or environmental factors. Molecular genetic studies later confirmed the genetic diversity of the disease.

A review published in 2004, which was based on 35 patients seen by the respective authors over 8 years and also a literature review of 220 cases of acquired partial lipodystrophy (APL), proposed an essential diagnostic criterion. Based on the review and the authors experience, they proposed that APL presents as a gradual onset of bilaterally symmetrical loss of subcutaneous fat from the face, neck, upper extremities, thorax, and abdomen, in the "cephalocaudal" sequence, sparing the lower extremities. The median age of the onset of lipodystrophy was seven years. Several autoimmune diseases, in particular systemic lupus erythematosus and dermatomyositis, were associated with APL. The prevalence rates of diabetes mellitus and impaired glucose tolerance were 6.7% and 8.9%, respectively. Around 83% of APL patients had low complement 3 (C3) levels and the presence of polyclonal immunoglobulin C3 nephritic factor. About 22% of patients developed membranoproliferative glomerulonephritis (MPGN) after a median of about 8 years following the onset of lipodystrophy. Compared with patients without renal disease, those with MPGN had earlier age of onset of lipodystrophy (12.6 ± 10.3 yr vs 7.7 ± 4.4 yr, respectively; p < 0.001) and a higher prevalence of C3 hypocomplementemia (78% vs 95%, respectively; p = 0.02).

The adipose stores of the gluteal regions and lower extremities (including soles) tend to be either preserved or increased, particularly among women. Variable fat loss of the palms, but no loss of intramarrow or retro-orbital fat, has been demonstrated.

Diagnostic procedures that may reveal muscular disorders include direct clinical observations. This usually starts with the observation of bulk, possible atrophy or loss of muscle tone. Neuromuscular disease can also be diagnosed by testing the levels of various chemicals and antigens in the blood, and using electrodiagnostic medicine tests including electromyography (measuring electrical activity in muscles) and nerve conduction studies.

In neuromuscular disease evaluation, it is important to perform musculoskeletal and neurologic examinations. Genetic testing is an important part of diagnosing inherited neuromuscular conditions.

The diagnosis of HSAN I is based on the observation of symptoms described above and is supported by a family history suggesting autosomal dominant inheritance. The diagnosis is also supported by additional tests, such as nerve conduction studies in the lower limbs to confirm a sensory and motor neuropathy. In sporadic cases, acquired neuropathies, such as the diabetic foot syndrome and alcoholic neuropathy, can be excluded by the use of magnetic resonance imaging and by interdisciplinary discussion between neurologists, dermatologists, and orthopedics.

The diagnosis of the disease has been revolutionized by the identification of the causative genes. The diagnosis is now based on the detection of the mutations by direct sequencing of the genes. Nevertheless, the accurate phenotyping of patients remains crucial in the diagnosis. For pregnant patients, termination of pregnancy is not recommended.

HSAN I must be distinguished from hereditary motor and sensory neuropathy (HMSN) and other types of hereditary sensory and autonomic neuropathies (HSAN II-V). The prominent sensory abnormalities and foot ulcerations are the only signs to separate HSAN I from HMSN. HSAN II can be differentiated from HSAN I as it is inherited as an autosomal recessive trait, it has earlier disease onset, the sensory loss is diffused to the whole body, and it has less or no motor symptoms. HSAN III-V can be easily distinguished from HSAN I because of congenital disease onset. Moreover, these types exhibit typical features, such as the predominant autonomic disturbances in HSAN III or congenital loss of pain and anhidrosis in HSAN IV.

HPS is one of the rare lung diseases currently being studied by The Rare Lung Diseases Consortium (RLDC). The RLDC is part of the Rare Diseases Clinical Research Network (RDCRN), an initiative of the Office of Rare Diseases Research (ORDR), of the National Center for Advancing Translational Sciences (NCATS). The RLDC is dedicated to developing new diagnostics and therapeutics for patients with rare lung diseases, through collaboration between the NIH, patient organizations and clinical investigators.

The diagnosis of HPS is established by clinical findings of hypopigmentation

of the skin and hair, characteristic eye findings, and demonstration of absent

dense bodies on whole mount electron microscopy of platelets. Molecular

genetic testing of the HPS1 gene is available on a clinical basis for

individuals from northwestern Puerto Rico. Molecular testing of the HPS3 gene

is available on a clinical basis for individuals of central Puerto Rican or

Ashkenazi Jewish heritage. Sequence analysis is available on a clinical basis

for mutations in HPS1 and HPS4. Diagnosis of individuals with other types of

HPS is available on a research basis only.

Heterogeneous medical condition in medicine are those medical conditions which have several etiologies, like hepatitis or diabetes. Medical conditions are normally defined pathologically (liver inflammation) or clinically (excessive urination) and not etiologically, and therefore it is normal to have more than one cause for them. The word is used as an opposition to homogeneous, meaning that given a group of patients, the disease is the same for all of them.

When a condition is heterogeneous, it is normally divided in endotypes.

An endotype is a subtype of a condition, which is defined by a distinct functional or pathobiological mechanism. This is distinct from a phenotype, which is any observable characteristic or trait of a disease, such as morphology, development, biochemical or physiological properties, or behavior, without any implication of a mechanism. It is envisaged that patients with a specific endotype present themselves within phenotypic clusters of diseases.

One example is asthma, which is considered to be a syndrome, consisting of a series of endotypes. This is related to the concept of disease entity

There is no cure or treatment for GSS. It can, however, be identified through genetic testing. GSS is the slowest to progress among human prion diseases. Duration of illness can range from 3 months to 13 years, with an average duration of 5 or 6 years.

These are also referred to as systemic autoimmune diseases. The autoimmune CTDs may have both genetic and environmental causes. Genetic factors may create a predisposition towards developing these autoimmune diseases. They are characterized as a group by the presence of spontaneous overactivity of the immune system that results in the production of extra antibodies into the circulation. The classic collagen vascular diseases have a "classic" presentation with typical findings that doctors can recognize during an examination. Each also has "classic" blood test abnormalities and abnormal antibody patterns. However, each of these diseases can evolve slowly or rapidly from very subtle abnormalities before demonstrating the classic features that help in the diagnosis. The classic collagen vascular diseases include:

- Systemic lupus erythematosus (SLE) – An inflammation of the connective tissues, SLE can afflict every organ system. It is up to nine times more common in women than men and strikes black women three times as often as white women. The condition is aggravated by sunlight.

- Rheumatoid arthritis – Rheumatoid arthritis is a systemic disorder in which immune cells attack and inflame the membrane around joints. It also can affect the heart, lungs, and eyes. Of the estimated 2.1 million Americans with rheumatoid arthritis, approximately 1.5 million (71 percent) are women.

- Scleroderma – an activation of immune cells that produces scar tissue in the skin, internal organs, and small blood vessels. It affects women three times more often than men overall, but increases to a rate 15 times greater for women during childbearing years, and appears to be more common among black women.

- Sjögren's syndrome – also called Sjögren's disease, is a chronic, slowly progressing inability to secrete saliva and tears. It can occur alone or with rheumatoid arthritis, scleroderma, or systemic lupus erythematosus. Nine out of 10 cases occur in women, most often at or around mid-life.

- Mixed connective tissue disease – Mixed connective-tissue disease (MCTD) is a disorder in which features of various connective-tissue diseases (CTDs) such as systemic lupus erythematosus (SLE); systemic sclerosis (SSc); dermatomyositis (DM); polymyositis (PM); anti-synthetase syndrome; and, occasionally, Sjögren syndrome can coexist and overlap. The course of the disease is chronic and usually milder than other CTDs. In most cases, MCTD is considered an intermediate stage of a disease that eventually becomes either SLE or Scleroderma.

- Undifferentiated connective tissue disease (UCTD) is a disease in which the body mistakenly attacks its own tissues. It is diagnosed when there is evidence of an existing autoimmune condition which does not meet the criteria for any specific autoimmune disease, such as systemic lupus erythematosus or scleroderma. Latent lupus and incomplete lupus are alternative terms that have been used to describe this condition.

- Psoriatic arthritis is also a collagen vascular disease.