What laboratory tests and treatments are used for vasculitis?

Laboratory Evaluation for Vasculitis

Essential Initial Laboratory Tests

For any patient with suspected vasculitis, obtain ANCA testing (both MPO and PR3 by high-quality antigen-specific immunoassays), complete blood count, inflammatory markers (ESR and CRP), comprehensive metabolic panel with renal function, and urinalysis with microscopy. 1, 2, 3

Core Laboratory Panel

• ANCA testing using high-quality antigen-specific immunoassays (ELISA) for MPO-ANCA and PR3-ANCA is the preferred screening method and should be performed first-line for suspected small-vessel vasculitis 1, 3
• Inflammatory markers including ESR and CRP are essential, as raised levels are highly sensitive for vasculitis diagnosis, though a normal ESR or CRP should raise suspicion for an alternative diagnosis 1, 3
• Complete blood count to assess for anemia, leukopenia, and calculate neutrophil-to-lymphocyte ratio 2, 4
• Comprehensive metabolic panel including serum creatinine to evaluate renal function 2, 4
• Urinalysis with microscopy is crucial to detect hematuria with dysmorphic red blood cells, red cell casts, and proteinuria that indicate renal involvement 1, 2, 3

Additional Serologic Testing

• Anti-nuclear antibodies (ANA) to assess for potential connective tissue diseases 2
• Anti-GBM antibodies are critical in pulmonary-renal syndrome, as a positive test suggests anti-GBM disease requiring urgent plasma exchange 1, 3
• Complement levels (C3, C4) should be measured in all patients 4
• Hepatitis B and C serology is extremely useful, particularly when liver involvement is present 4, 5
• Cryoglobulin and immunoglobulin levels should be obtained 5

Critical Clinical Scenarios

Pulmonary-Renal Syndrome

In patients presenting with acute kidney injury and alveolar hemorrhage, immediately obtain both ANCA and anti-GBM antibody testing, as positive anti-GBM antibodies require urgent plasma exchange without waiting for biopsy confirmation. 1, 3

• This presentation affects 10% of ANCA-associated vasculitis patients and carries increased mortality risk 1, 3
• Positive MPO- or PR3-ANCA supports ANCA-associated vasculitis diagnosis 1, 3
• Some patients test positive for both ANCA and anti-GBM antibodies 1

Rapidly Deteriorating Patients

When clinical presentation is compatible with small-vessel vasculitis and MPO- or PR3-ANCA is positive, start immunosuppressive therapy immediately without waiting for kidney biopsy results, especially in rapidly deteriorating patients. 1, 3

• About 90% of patients with small-vessel vasculitis or necrotizing crescentic glomerulonephritis have ANCA positivity 1
• However, approximately 10% of patients with clinical features of ANCA-associated vasculitis are persistently ANCA-negative and require tissue biopsy for definitive diagnosis 1, 2, 3

Tissue Biopsy Considerations

• Kidney biopsy remains the gold standard, providing both diagnostic confirmation and prognostic information through assessment of glomerular, tubulointerstitial, and vascular histopathology, with diagnostic yield as high as 91.5% in granulomatosis with polyangiitis 1, 2, 3
• Temporal artery biopsy should be performed whenever giant cell arteritis is suspected (at least 1 cm length), but treatment with high-dose glucocorticoids should not be delayed while awaiting biopsy 1
• Biopsy should not be delayed beyond 1-2 weeks after commencing glucocorticoid therapy 1

Specialized Testing for Specific Vasculitis Types

Large Vessel Vasculitis

• Ultrasound of temporal artery shows 88% sensitivity and 97% specificity for giant cell arteritis 1, 3
• FDG-PET/CT is valuable for diagnosis, showing inflammatory cell accumulation in vessel walls 3
• MRI/MRA or PET for thorough assessment of the arterial tree 3

Renal Involvement

• 24-hour urine collection for protein and creatinine clearance when renal involvement is suspected 2
• Typical findings include microscopic hematuria with dysmorphic red blood cells, red cell casts, and moderate proteinuria (1-3 g/day) 1

Important Caveats

• ANCA-negative vasculitis occurs in approximately 10% of cases and requires the same treatment approach as ANCA-positive disease, though no studies have specifically focused on this population 1, 2, 3
• P-ANCA can be found in conditions beyond vasculitis, including autoimmune hepatitis, primary sclerosing cholangitis, and inflammatory bowel disease, requiring clinical correlation 6
• Approximately 5% of granulomatosis with polyangiitis patients can have P-ANCA/MPO positivity 6
• Serial ANCA measurements can be useful for predicting relapse in some patients 6