Which lab tests are useful in the evaluation of suspected vasculitis

Which lab tests are useful in the evaluation of suspected vasculitis?

  • • Tests suggesting systemic inflammation:

Complete blood count: look for anemia of chronic disease and thrombocytosis. White blood cell count and differential to look for neutrophilia or eosinophilia. Pearl: Note that primary systemic vasculitis never causes pancytopenia (must rule out SLE, B-cell lymphoma, myeloma, leukemia).

Westergren erythrocyte sedimentation rate >100 mm/hour and C-reactive protein >10 mg/dL in the absence of bacterial infection and widespread cancer should suggest vasculitis.

Low albumin: this is a negative acute-phase reactant and decreases with systemic inflammation.

  • • Tests suggesting organ involvement:

Creatinine and urinalysis.

Liver-associated enzymes: if extremely elevated, consider hepatitis B/C.

Creatine kinase.

Lumbar puncture with cerebrospinal fluid analysis: if CNS symptoms.

Stool for occult blood.

Chest radiograph.

Electromyography (EMG) and nerve conduction velocity (NCV): if neuropathy symptoms.

Brain magnetic resonance imaging or an abdominal computed tomography (CT) scan if symptoms suggest involvement.

  • • Tests suggesting immune complex formation and/or deposition:

RF and ANA. Pearl: RF and ANA should not be positive in primary systemic vasculitis. If RF is positive, consider cryoglobulinemia and SBE. If ANA is positive, consider SLE or Sjögren’s syndrome.

Anti-C1q: if history of urticarial vasculitis.

Cryoglobulins: if positive, rule out hepatitis C.

Complement levels—C3/C4 are low in cryoglobulinemia, hypocomplementemic urticarial vasculitis, and SLE. Other vasculitides usually have normal values except PAN, where they are low in up to 25% of cases, and in some cases of hypersensitivity vasculitides.

  • • Tests suggesting ANCA-related vasculitis:

c-ANCA: if against serine proteinase 3, usually GPA; sometimes MPA.

p-ANCA: if against myeloperoxidase, consider MPA and EGPA; sometimes GPA.

Eosinophil count/IgE level if suspect EGPA.

Pearl: Cocaine-associated vasculitis can be c-ANCA, p-ANCA, and/or atypical ANCA (antihuman neutrophil elastase)-positive.

  • • Tests suggesting etiology:

Blood cultures: rule out SBE.

Infectious serologies: Hep BsAg (PAN), hepatitis C (cryoglobulinemia), parvovirus IgM (GPA, PAN), herpes (IgM and PCR), cytomegalovirus (IgM and PCR), Epstein–Barr virus (IgM and PCR), HIV (any vasculitis).

Antiglomerular basement membrane antibody: any patient with pulmonary–renal syndrome.

Serum protein electrophoresis: rule out myeloma.

Cerebrospinal fluid studies: herpes, varicella-zoster virus (VZV DNA and anti-VZV antibody).

Urinary toxicology screen: rule out cocaine use.

Not all of these tests are ordered for all patients. The physician must choose which test to order according to the clinical situation.


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