The diagnostic testing for vasculitis should be guided by the patient's history and physical exam. The clinician should ask about the duration, onset, and presence any associated symptoms such as weight loss or fatigue (that would indicate a systemic cause). It is important to distinguish between IgA and non-IgA vasculitis. IgA vasculitis is more likely to present with abdominal pain, bloody urine, and joint pain. In the case that the cause is not obvious, a reasonable initial workup would include a complete blood count, urinalysis, basic metabolic panel, fecal occult blood testing, erythrocyte sedimentation rate (ESR), and C-reactive protein level. Small vessel cutaneous vasculitis is a diagnosis of exclusion and requires ruling out systemic causes of the skin findings. Skin biopsy (punch or excisional) is the most definitive diagnostic test and should be performed with 48 hours of appearance of the vasculitis. A skin biopsy will be able to determine if the clinical findings are truly due to a vasculitis or due to some other cause.

A detailed history is important to elicit any recent medications, any risk of hepatitis infection, or any recent diagnosis with a connective tissue disorder such as systemic lupus erythematosus (SLE). A thorough physical exam is needed as usual.

- Lab tests. Basic lab tests may include a CBC, chem-7 (look for creatinine), muscle enzyme, liver function tests, ESR, hepatitis seroloties, urinalysis, CXR, and EKG. Additional, more specific tests include:

- Antinuclear antibody (ANA) test can detect an underlying connective tissue disorder, especially SLE

- Complement levels that are low can suggest mixed cryoglobulinemia, hepatitis C infection, and SLE, but not most other vasculitides.

- Antineutrophil cytoplasmic antibody (ANCA) may highly suggest granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis, or drug-induced vasculitis, but is not diagnostic.

- Electromyography. It is useful if a systemic vasculitis is suspected and neuromuscular symptoms are present.

- Arteriography. Arteriograms are helpful in vasculitis affecting the large and medium vessels but not helpful in small vessel vasculitis. Angiograms of mesenteri or renal arteries in polyarteritis nodosa may show aneurysms, occlusions, and vascular wall abnormalities. Arteriography are not diagnostic in itself if other accessible areas for biopsy are present. However, in Takayasu's arteritis, where the aorta may be involved, it is unlikely a biopsy will be successful and angiography can be diagnostic.

- Tissue biopsy. This is the gold standard of diagnosis when biopsy is taken from the most involved area.

Laboratory tests may reveal an increased sedimentation rate, elevated CRP, anemia and elevated creatinine due to kidney impairment. An important diagnostic test is the presence of perinuclear antineutrophil cytoplasmic antibodies (p-ANCA) with myeloperoxidase specificity (a constituent of neutrophil granules), and protein and red blood cells in the urine.

In patients with neuropathy, electromyography may reveal a sensorimotor peripheral neuropathy.

Diagnostic markers include eosinophil granulocytes and granulomas in affected tissue, and antineutrophil cytoplasmic antibodies (ANCA) against neutrophil granulocytes. The American College of Rheumatology 1990 criteria for diagnosis of Churg–Strauss syndrome lists these criteria:

- Asthma

- Eosinophilia, i.e. eosinophil blood count greater than 500/microliter, or hypereosinophilia, i.e. eosinophil blood count greater than 1,500/microliter

- Presence of mononeuropathy or polyneuropathy

- Unfixed pulmonary infiltrates

- Presence of paranasal sinus abnormalities

- Histological evidence of extravascular eosinophils

For classification purposes, a patient shall be said to have Churg–Strauss syndrome (CSS) if at least four of these six criteria are positive. The presence of any four or more of the six criteria yields a sensitivity of 85% and a specificity of 99.7%.

Granulomatosis with polyangiitis is usually suspected only when a person has had unexplained symptoms for a long period of time. Determination of Anti-neutrophil cytoplasmic antibodies (ANCAs) can aid in the diagnosis, but positivity is not conclusive and negative ANCAs are not sufficient to reject the diagnosis. Cytoplasmic-staining ANCAs that react with the enzyme proteinase 3 (cANCA) in neutrophils (a type of white blood cell) are associated with GPA.

If the person has kidney failure or cutaneous vasculitis, a biopsy is obtained from the kidneys. On rare occasions, thoracoscopic lung biopsy is required. On histopathological examination, a biopsy will show "leukocytoclastic vasculitis" with necrotic changes and granulomatous inflammation (clumps of typically arranged white blood cells) on microscopy. These granulomas are the main reason for the name granulomatosis with polyangiitis, although it is not an essential feature. Nevertheless, necrotizing granulomas are a hallmark of this disease. However, many biopsies can be nonspecific and 50% provide too little information for the diagnosis of GPA.

In this table: ANA = Antinuclear antibodies, CRP = C-reactive protein, ESR = Erythrocyte Sedimentation Rate, "ds"DNA = double-stranded DNA, ENA = extractable nuclear antigens, RNP = ribonucleoproteins; VDRL = Venereal Disease Research Laboratory

The French Vasculitis Study Group has developed a five-point system ("five-factor score") that predicts the risk of death in Churg–Strauss syndrome using clinical presentations. These factors are:

- Reduced renal function (creatinine >1.58 mg/dl or 140 µmol/l)

- Proteinuria (>1 g/24h)

- Gastrointestinal hemorrhage, infarction, or pancreatitis

- Involvement of the central nervous system

- Cardiomyopathy

The lack of any of these factors indicates milder case, with a five-year mortality rate of 11.9%. The presence of one factor indicates severe disease, with a five-year mortality rate of 26%, and two or more indicate very severe disease: 46% five-year mortality rate.

In 1990, the American College of Rheumatology accepted classification criteria for GPA. These criteria were not intended for diagnosis, but for inclusion in randomized controlled trials. Two or more positive criteria have a sensitivity of 88.2% and a specificity of 92.0% of describing GPA.

- Nasal or oral inflammation:

- painful or painless oral ulcers "or"

- purulent or bloody nasal discharge

- Lungs: abnormal chest X-ray with:

- nodules,

- infiltrates "or"

- cavities

- Kidneys: urinary sediment with:

- microhematuria "or"

- red cell casts

- Biopsy: granulomatous inflammation

- within the arterial wall "or"

- in the perivascular area

According to the Chapel Hill Consensus Conference (CHCC) on the nomenclature of systemic vasculitis (1992), establishing the diagnosis of GPA demands:

- a granulomatous inflammation involving the respiratory tract, and

- a vasculitis of small to medium-size vessels.

Several investigators have compared the ACR and Chapel Hill criteria.

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.

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 customary treatment involves long term dosage of prednisone, alternated or combined with cytotoxic drugs, such as cyclophosphamide or azathioprine.

Plasmapheresis may also be indicated in the acute setting to remove ANCA antibodies.

Rituximab has been investigated, and in April 2011 approved by the FDA when used in combination with glucocorticoids in adult patients.

No specific lab tests exist for diagnosing polyarteritis nodosa. Diagnosis is generally based on the physical examination and a few laboratory studies that help confirm the diagnosis:

A patient is said to have polyarteritis nodosa if he or she has three of the 10 signs known as the 1990 American College of Rheumatology (ACR) criteria, when a radiographic or pathological diagnosis of vasculitis is made:

In polyarteritis nodosa, small aneurysms are strung like the beads of a rosary, therefore making "rosary sign" an important diagnostic feature of the vasculitis. The 1990 ACR criteria were designed for classification purposes only. Nevertheless, their good discriminatory performances, indicated by the initial ACR analysis, suggested their potential usefulness for diagnostic purposes as well. Subsequent studies did not confirm their diagnostic utility, demonstrating a significant dependence of their discriminative abilities on the prevalence of the various vasculitides in the analyzed populations. Recently, an original study, combining the analysis of more than 100 items used to describe patients' characteristics in a large sample of vasculitides with a computer simulation technique designed to test the potential diagnostic utility of the various criteria, proposed a set of eight positively or negatively discriminating items to be used as a screening tool for diagnosis in patients suspected of systemic vasculitis.

Antibodies are usually raised against foreign proteins, such as those made by a replicating virus or invading bacterium. Virus or bacteria with antibodies opsonized or "stuck" to them highlight them to other cells of the immune system for clearance.

Antibodies against self proteins are known as autoantibodies, and are not found in healthy individuals. These autoantibodies can be used to detect certain diseases.

Cryoglobulinemia and cryoglobulinemic disease must be distinguished from cryofibrinogenemia or cryofibrinogenemic disease, conditions which involve the cold-induced intravascular deposition of circulating native fibrinogens. The cryoglobulins in plasma or serum precipitate at lower temperatures (e.g. 4°C). Since cryofibrinogens are present in plasma but greatly depleted in serum, precipitation tests for them are positive in plasma but negative in serum. Cryofibrinogenemia is occasionally found in cases of cryoglobulinemic disease. Cryoglobulinemic disease must also be distinguished from frostbite as well as numerous other conditions that have a clinical (particularly cutaneous) presentation similar to cryoglobulinemic disease but are not exacerbated by cold temperature, e.g. dysfibrinogenemia and dysfibrinogenemic disease (conditions involving the intravascular deposition of genetically abnormal circulating fibrinogens), purpura fulminans, cholesterol emboli, warfarin necrosis, ecthyma gangrenosum, and various hypercoagulable states.

Rheumatoid factor is a sensitive test for cryoglobulinemia. The precipitated cryoglobulins are examined by immunoelectrophoresis and immunofixation to detect and quantify the presence of monoclonal IgG, IgM, IgA, κ light chain, or λ light chain immunoglobins. Other routine tests include measuring blood levels of rheumatoid factor activity, complement C4, other complement components, and hepatitic C antigen. Biopsies of skin lesions and, where indicated, kidney or other tissues can help in determining the nature of the vascular disease (immunoglobulin deposition, cryoglobulinemic vasculitis, or, in cases showing the presence of cryfibrinogenemia, fibrinogen deposition. In all events, further studies to determine the presence of hematological, infections, and autoimmune disorders are conducted on the basis of these findings as well as each cases clinical findings.

Treatment is targeted to the underlying cause. However, most vasculitis in general are treated with steroids (e.g. methylprednisolone) because the underlying cause of the vasculitis is due to hyperactive immunological damage. Immunosuppressants such as cyclophosphamide and azathioprine may also be given.

A systematic review of antineutrophil cytoplasmic antibody (ANCA) positive vasculitis identified best treatments depending on whether the goal is to induce remission or maintenance and depending on severity of the vasculitis.

Treatment should be directed towards the specific underlying cause of the vasculitis. If no underlying cause is found and the vasculitis is truly limited to the skin then treatment is primarily supportive. Such treatment involves measures such as leg elevation, stockings, and topical steroids to relieve itching/burning. If the vasculitis does not self-resolve within 3–4 weeks, more aggressive treatment may be warranted. Oral colchicine or dapsone are often used for this purpose. If rapid control of symptoms is needed, a short course of high-dose oral steroids may be given. Immunosuppressive agents such as methotrexate and azathioprine may be used in truly refractory cases not responsive to colchicine or dapsone.

Pauci-immune (pauci- Latin: few, little) vasculitis is a form of vasculitis that is associated with minimal evidence of hypersensitivity upon immunofluorescent staining for IgG.

Normally a kidney sample will be subjected to immunofluorescence if rapidly progressive glomerulonephritis is a concern. In this case, the immunofluorescence can show three patterns: linear, granular and negative (pauci-immune). The linear and granular patterns are examples of positive immunofluorescence and are associated with Goodpasture syndrome and post-streptococcal glomerulonephritis accordingly. A negative pattern or pauci-immune pattern can be associated with systemic vasculitis such as microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis (EGPA) or granulomatosis with polyangiitis (GPA). In many cases however, it is limited to the kidney and it is thus called idiopathic.

Since it can be associated with the three systemic vasculitides mentioned above, a pauci-immune pattern finding can be associated with antineutrophil cytoplasmic antibodies (ANCA). Therefore, an ANCA test should follow a negative immunofluorescence result in order to distinguish between the above-mentioned systemic vasculitis.

Peak incidences in 50- to 60-year-olds symptoms include intermittent fever / weight loss / shortness of breath / joint pain.

Proximal muscle weakness, characteristic skin rash and elevated muscle enzymes are routinely used to identify JDM. Typical magnetic resonance imaging and muscle biopsy changes are considered the next most useful diagnostic criteria, followed by myopathic changes on electromyogram, calcinosis, dysphonia and nailfold capillaroscopy. Other useful criteria include myositis-specific or -related antibodies, nailfold capillaroscopy, factor VIII-related antigen, muscle ultrasound, calcinosis and neopterin.

A rare autoimmune disease characterized by recurrent urticaria (nettle rash), first described in the 1970s. There is no defined paradigm for the syndrome aetiology and severity in progression. Diagnosis is confirmed with the identification of at least two conditions from: venulitis on skin biopsy, arthritis, ocular inflammation, abdominal pain or positive C1q antibodies to immune complexes. It is this last category, anti-C1q antibodies, that all HUV patients test positive for. "In vitro" experiments and mouse models of the disease have not thoroughly determined the link between these antibodies and the disease, even though the link is so pronounced.

Patients presenting with acute episodes often have high levels of inflammatory markers such as erythrocyte sedimentation rate or C-reactive protein, ESR or CRP. Patients often have cartilage-specific antibodies present during acute relapsing polychondritis episodes. Antinuclear antibody reflexive panel, rheumatoid factor, and antiphospholipid antibodies are tests that may assist in the evaluation and diagnosis of autoimmune connective-tissue diseases.

FDG positron emission tomography (PET) may be useful to detect the condition early. Other imaging studies including MRI, CT scans, and X-rays may reveal inflammation and/or damaged cartilage facilitating diagnosis.

Henoch–Schönlein purpura may present with an atypical manifestation, which can be confused with papular urticaria, systemic lupus erythematosus, meningococcemia, dermatitis herpetiformis, and acute hemorrhagic edema of infancy.

Of the children diagnosed with and treated for JDM, about half will recover completely. Close to 30 percent will have weakness after the disease resolves. Most children will go into remission and have their medications eliminated within two years, while others may take longer to respond or have more severe symptoms that take longer to clear up.

A common lasting effect of JDM is childhood arthritis.

Multiple standards exist for defining Henoch–Schönlein purpura, including the 1990 American College of Rheumatology (ACR) classification and the 1994 Chapel Hill Consensus Conference (CHCC). Some have reported the ACR criteria to be more sensitive than those of the CHCC.

More recent classifications, the 2006 European League Against Rheumatism (EULAR) and Pediatric Rheumatology Society (PReS) classification, include palpable purpura as a mandatory criterion, together with at least one of the following findings: diffuse abdominal pain, predominant IgA deposition (confirmed on skin biopsy), acute arthritis in any joint, and renal involvement (as evidenced by the presence of blood and/or protein in the urine).

Treatments are generally directed toward stopping the inflammation and suppressing the immune system. Typically, corticosteroids such as prednisone are used. Additionally, other immune suppression drugs, such as cyclophosphamide and others, are considered. In case of an infection, antimicrobial agents including cephalexin may be prescribed. Affected organs (such as the heart or lungs) may require specific medical treatment intended to improve their function during the active phase of the disease.