What lab workup and treatment is recommended for a suspected case of vasculitis in an adult patient?

Laboratory Workup for Suspected Vasculitis

All patients with suspected vasculitis require a structured laboratory evaluation including complete blood count, comprehensive metabolic panel, ESR, CRP, urinalysis, and ANCA testing using both indirect immunofluorescence and antigen-specific immunoassays, with the 2017 consensus recommending high-quality antigen-specific immunoassays as the preferred screening method. 1, 2, 3

Essential Initial Laboratory Tests

Core Laboratory Panel

• Complete blood count with differential to assess for anemia, leukocytosis, thrombocytosis, or cytopenias that may indicate active inflammation or bone marrow suppression 1, 4, 5
• Comprehensive metabolic panel including serum creatinine to evaluate renal function, as acute kidney injury is common in vasculitis 1, 2, 4
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as inflammatory markers, though these are nonspecific and cannot distinguish vasculitis activity from infection 6, 3, 5
• Urinalysis is crucial at every visit to detect hematuria, proteinuria, and red cell casts suggesting glomerulonephritis 6, 1, 2, 4

Autoimmune Serologies

• ANCA testing using both indirect immunofluorescence and ELISA is essential when small vessel vasculitis is suspected, with the 2017 revised consensus stating that high-quality antigen-specific immunoassays (MPO-ANCA and PR3-ANCA) are the preferred screening methodology 1, 2, 3
• Anti-nuclear antibodies (ANA) should be evaluated to assess for connective tissue diseases that can present with secondary vasculitis 4, 5
• Anti-glomerular basement membrane (anti-GBM) antibodies when pulmonary-renal syndrome is present, as positive anti-GBM suggests anti-GBM disease while positive MPO or PR3-ANCA supports ANCA-associated vasculitis 2
• Complement levels (C3, C4) should be measured, as low levels may indicate immune complex-mediated vasculitis 3, 5
• Anti-C1q antibodies are helpful in immune complex-associated small-vessel vasculitis 3

Additional Serologic Testing

• Cryoglobulin testing should be performed when HCV-related vasculitis or mixed cryoglobulinemia is suspected 6, 5
• Hepatitis B and C serology is extremely useful, particularly when liver involvement is present or risk factors exist 3, 5
• Immunoglobulin levels (IgA, IgG, IgM) to assess for hypogammaglobulinemia, which can occur with certain vasculitides or immunosuppressive therapy 7, 3

Organ-Specific Laboratory Evaluation

Renal Assessment

• 24-hour urine collection for protein and creatinine clearance when renal involvement is suspected 4
• Kidney biopsy provides both diagnostic and prognostic information through assessment of glomerular, tubulointerstitial, and vascular histopathology, with diagnostic yield over 70% 2

Neurologic Assessment

• Cerebrospinal fluid analysis may reveal increased opening pressure, elevated protein, or lymphocytic pleocytosis in CNS vasculitis 1
• Electromyography with peripheral nerve neurophysiological tests for suspected peripheral neuropathy 6

Important Clinical Caveats

• About 10% of patients with clinical features of ANCA-associated vasculitis may be ANCA-negative, requiring tissue biopsy for definitive diagnosis 2, 4
• ESR and CRP are nonspecific and cannot distinguish between vasculitis disease activity and concomitant infection or other inflammatory sources 3
• ANCA testing should inform clinical suspicion but not drive treatment changes alone—structured clinical assessment using tools like the Birmingham Vasculitis Activity Score (BVAS) should guide therapeutic decisions 6, 2
• Serial ANCA measurements have controversial utility for predicting relapse; some studies show patients with persistent, rising, or newly positive ANCA have higher relapse incidence, while others do not confirm this association 6

Imaging Studies by Vessel Size

Large Vessel Vasculitis

• Temporal artery ultrasound shows 88% sensitivity and 97% specificity for diagnosing giant cell arteritis 1, 2
• MRI/MRA of head, neck, and affected arterial territories can identify extracranial large artery involvement with high accuracy 1
• FDG-PET/CT demonstrates inflammatory cell accumulation in vessel walls and should be performed after 6 hours of fasting with 120-180 minute delay after injection 1

CNS Vasculitis

• MRI brain is the preferred initial imaging modality with abnormal findings in >90% of cases, though findings are not diagnostic 6, 1
• Brain biopsy is the most specific diagnostic test for diffuse or multifocal CNS vasculitis but is limited by its invasive nature 1

Medium and Small Vessel Vasculitis

• Chest imaging (X-ray or CT) to evaluate for pulmonary involvement, granulomas, infiltrates, or cavitary lesions 4
• Tissue biopsy of affected organs remains the gold standard for diagnosis, with diagnostic yield over 70% depending on the organ sampled 2

Monitoring During Follow-Up

• Urinalysis at every clinic visit to screen for infection, renal relapse, or bladder complications from cyclophosphamide 6
• Inflammatory markers and renal function every 1-3 months to monitor disease status 6
• Complete blood count and liver function tests at similar intervals to screen for drug toxicity, with acute fall in white cell count requiring dose reduction or discontinuation of immunosuppressives 6
• Blood glucose monitoring while on glucocorticoid therapy 6
• Investigation of persistent unexplained hematuria in patients with prior cyclophosphamide exposure, as transitional cell cancer can occur months to years after exposure 6