PR3-ANCA (C-ANCA)

Immunity

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Associated with a Cytoplasmic (C-ANCA) staining pattern on immunofluorescence

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PR3 - ANCA (C-ANCA) Comprehensive Guide

Why is it done?
- Detection of anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase-3 (PR3) antigen in serum
- Diagnosis of granulomatosis with polyangiitis (GPA), formerly known as Wegener's granulomatosis
- Investigation of suspected systemic vasculitis affecting small and medium-sized blood vessels
- Evaluation of patients presenting with upper respiratory tract involvement, pulmonary symptoms, or glomerulonephritis
- Monitoring disease activity and treatment response in patients with confirmed ANCA-associated vasculitis
- Differentiation between GPA and other forms of vasculitis or pulmonary-renal syndromes
- Assessment during active disease phases or suspected relapse
Normal Range
- Normal/Reference Value: Negative (less than 1.0 U/mL or undetectable)
- Units of Measurement: U/mL (Units per milliliter) or ELISA index
- Negative Result: Indicates absence of PR3-ANCA antibodies; generally excludes diagnosis of GPA in typical presentations
- Borderline/Weakly Positive (1.0-1.5 U/mL): Requires clinical correlation and possible repeat testing; may warrant additional confirmation
- Positive Result (>1.5 U/mL or clearly positive): Suggestive of ANCA-associated vasculitis, particularly GPA; higher titers correlate with active disease
- Very High Positive (>20 U/mL): Indicates significant disease activity; may be associated with organ involvement and systemic symptoms
Interpretation
- Positive PR3-ANCA with Clinical Symptoms: Highly specific for GPA diagnosis; clinical presentation includes upper respiratory tract involvement (sinusitis, nasal ulcers), lower respiratory tract disease (pulmonary nodules, infiltrates), and glomerulonephritis (hematuria, proteinuria, renal insufficiency)
- Negative PR3-ANCA: Does not exclude GPA, particularly in limited or early-stage disease; approximately 10-15% of GPA patients are ANCA-negative; requires consideration of alternative diagnoses or tissue biopsy confirmation
- Titer Level Correlation: Higher PR3-ANCA titers typically correlate with active disease, systemic manifestations, and organ involvement; falling titers may indicate therapeutic response; rising titers may precede clinical relapse
- PR3-ANCA vs MPO-ANCA: PR3-ANCA (cytoplasmic pattern, C-ANCA) is associated with GPA; MPO-ANCA (perinuclear pattern, P-ANCA) is associated with microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis
- Factors Affecting Results: Immunosuppressive therapy may reduce or eliminate antibody titers; timing relative to disease flare affects sensitivity; some patients develop ANCA-negative disease during remission; technical factors and laboratory standardization differences may influence results
- Clinical Significance: Positive results strongly suggest active ANCA-associated vasculitis; when combined with tissue biopsy findings (necrotizing granulomatous inflammation, necrotizing vasculitis) and clinical presentation, establishes GPA diagnosis with high specificity
Associated Organs
- Primary Organ Systems Involved:
- Upper Respiratory Tract: Chronic sinusitis, nasal congestion, nasal ulcerations, epistaxis, septal perforation, nasopharyngeal involvement
- Lower Respiratory Tract: Pulmonary nodules, infiltrates, hemoptysis, dyspnea, pulmonary hemorrhage, bronchial stenosis
- Kidneys: Necrotizing glomerulonephritis (most common renal involvement), hematuria, proteinuria, rapidly progressive glomerulonephritis (RPGN), renal failure requiring dialysis
- Peripheral Nervous System: Peripheral neuropathy (particularly mononeuritis multiplex), sensory or motor deficits
- Skin: Palpable purpura, ulcers, necrotic lesions, urticarial manifestations
- Eyes: Scleritis, uveitis, keratitis, orbital involvement, vision-threatening complications
- Heart: Coronary vasculitis (rare), myocardial involvement, valvular disease, pericarditis
- Gastrointestinal Tract: Abdominal pain, nausea, mesenteric ischemia, gastrointestinal bleeding (less common)
- Associated Diseases and Complications:
- Granulomatosis with Polyangiitis (GPA) - primary disease association; Rapidly Progressive Glomerulonephritis (RPGN); End-stage renal disease requiring dialysis or transplantation; Infections (due to immunosuppressive therapy); Severe pulmonary hemorrhage; Hearing loss; Chronic organ dysfunction following disease resolution
Follow-up Tests
- Confirmatory and Diagnostic Tests:
- Immunofluorescence Microscopy/Indirect Immunofluorescence (IIF): Confirms cytoplasmic (C-ANCA) pattern; differentiates from perinuclear (P-ANCA) patterns
- MPO-ANCA (Anti-Myeloperoxidase): To rule out other ANCA-associated vasculitides (microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis)
- Tissue Biopsy: Upper or lower respiratory tract biopsy for necrotizing granulomatous inflammation; renal biopsy for necrotizing and crescentic glomerulonephritis; confirms GPA diagnosis definitively
- Imaging Studies:
- Chest X-ray or High-Resolution CT Chest: Evaluate pulmonary nodules, infiltrates, cavitary lesions, hemorrhage
- Sinus CT Imaging: Assess for sinusitis, bone erosion, nasal involvement
- Laboratory Tests for Organ Function:
- Serum Creatinine and BUN: Assess renal function; baseline and serial monitoring
- Estimated GFR (eGFR): Quantify glomerular filtration rate changes
- Urinalysis and 24-Hour Urine Protein: Detect hematuria, proteinuria, cellular casts indicating glomerulonephritis
- Complete Blood Count (CBC): Assess for anemia, leukopenia, thrombocytopenia; baseline before immunosuppressive therapy
- Comprehensive Metabolic Panel: Liver function tests, electrolytes; monitor during treatment
- Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): Non-specific markers of inflammation; used to monitor disease activity alongside PR3-ANCA titers
- Monitoring and Disease Follow-up:
- Serial PR3-ANCA Testing: Every 3-6 months during initial treatment; every 6-12 months during remission; more frequently if clinical concern for relapse; helps guide therapy adjustments
- Renal Function Monitoring: Monthly during induction therapy; every 3 months during maintenance; baseline renal biopsy if rapid rise in creatinine or heavy proteinuria
- Periodic Imaging: Chest imaging annually or as clinically indicated; sinus imaging if symptoms persist
- Pulmonary Function Tests: Baseline and periodic assessment if pulmonary involvement; assess for chronic lung disease sequelae
- Treatment-Related Monitoring: Baseline and periodic CBC, liver function tests if cyclophosphamide or azathioprine used; bone density screening; glucose monitoring if corticosteroids used long-term; infertility counseling for cyclophosphamide
Fasting Required?
- Fasting Status: No - Fasting is NOT required for PR3-ANCA testing
- Specimen Collection: Non-fasting blood sample (serum) can be drawn at any time of day; no dietary restrictions necessary
- Medications: Do NOT discontinue any medications prior to testing; continue all current medications including corticosteroids, immunosuppressants, and other treatments as prescribed; medications do not interfere with PR3-ANCA assay results
- Patient Preparation: Wear loose, comfortable clothing with accessible arms for phlebotomy; avoid excessive caffeine consumption immediately before testing; stay well-hydrated; minimal physical exertion on day of test is beneficial but not mandatory
- Specimen Requirements: Serum sample collected in standard serum separator tube (SST); typically 3-5 mL required; sample should be centrifuged within 1-2 hours of collection; separated serum can be refrigerated if testing delayed; stable at 2-8°C for several days
- Special Instructions: Report any recent infections or acute illnesses to healthcare provider; inform laboratory of current medications and immunosuppressive therapy; note timing relative to disease flares or treatment initiation; provide clinical information (symptoms, relevant organ involvement) to laboratory for interpretation context

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