ANCA by IFA reflex MPO/PR3 Antibodies Serum

Immunity

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Detects anti-neutrophil cytoplasmic antibodies; reflexes to MPO/PR3 subtyping.

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ANCA by IFA reflex MPO/PR3 Antibodies Serum - Comprehensive Test Guide

Section 1: Why is it done?
- Test Overview: This test detects anti-neutrophil cytoplasmic antibodies (ANCA) using Immunofluorescence Assay (IFA) with reflex testing to identify specific antibodies against Myeloperoxidase (MPO) and Proteinase-3 (PR3), which are markers of systemic vasculitis.
- Primary Indications for Testing:
- Investigation of suspected ANCA-associated vasculitis (AAV) in patients with systemic symptoms
- Diagnosis and differentiation of microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA)
- Evaluation of patients presenting with rapidly progressive glomerulonephritis (RPGN) or pulmonary-renal syndrome
- Assessment of constitutional symptoms including fever, weight loss, and malaise in conjunction with organ involvement
- Monitoring of disease activity and progression in known vasculitis cases
- Typical Clinical Circumstances:
- Performed during acute presentation with upper and lower respiratory tract involvement, hematuria, or proteinuria
- Testing occurs upon clinical suspicion of systemic vasculitis or when other autoimmune disease tests are inconclusive
- Baseline testing at diagnosis followed by serial testing every 3-6 months during treatment and remission maintenance
Section 2: Normal Range
- ANCA Screening (IFA):
- Normal Result: NEGATIVE (no ANCA antibodies detected on immunofluorescence) Units: Qualitative result
- Abnormal Result: POSITIVE (ANCA antibodies detected)
- Reflex MPO/PR3 Antibody Specificity Testing (performed if IFA positive):
- MPO Antibodies (Myeloperoxidase): Normal: <1.0 U/mL or Negative Borderline: 1.0-2.0 U/mL Positive: >2.0 U/mL Units: U/mL (Units per milliliter)
- PR3 Antibodies (Proteinase-3, c-ANCA associated): Normal: <1.0 U/mL or Negative Borderline: 1.0-2.0 U/mL Positive: >2.0 U/mL Units: U/mL (Units per milliliter)
- Interpretation Framework:
- NEGATIVE IFA with NEGATIVE reflex: Normal result - no vasculitis antibodies detected; vasculitis unlikely if clinical suspicion is low
- POSITIVE IFA + MPO POSITIVE: Indicates p-ANCA pattern; associated with MPO-ANCA-associated vasculitis (usually MPA or EGPA)
- POSITIVE IFA + PR3 POSITIVE: Indicates c-ANCA pattern; associated with PR3-ANCA-associated vasculitis (usually GPA)
- POSITIVE IFA + BOTH MPO and PR3 NEGATIVE: May indicate atypical ANCA; require further evaluation
Section 3: Interpretation
- Understanding Result Values:
- c-ANCA (Cytoplasmic ANCA) with PR3 Positivity: Indicates PR3-ANCA-associated vasculitis, strongly associated with Granulomatosis with Polyangiitis (GPA) Characterized by upper respiratory tract involvement (sinusitis, epistaxis), lower respiratory tract disease (hemoptysis, nodules), and glomerulonephritis Higher titers correlate with active disease; titers may decline with effective treatment
- p-ANCA (Perinuclear ANCA) with MPO Positivity: Indicates MPO-ANCA-associated vasculitis, primarily associated with Microscopic Polyangiitis (MPA) and Eosinophilic Granulomatosis with Polyangiitis (EGPA) MPA presents with pulmonary-renal syndrome and glomerulonephritis without upper respiratory involvement EGPA includes asthma history, eosinophilia, and systemic involvement
- Clinical Significance of Different Patterns:
- High Titer Results (>20 U/mL): Strongly suggestive of active vasculitis Greater diagnostic confidence Often correlates with more severe clinical manifestations Baseline for future comparison during treatment monitoring
- Borderline to Moderate Titers (2-10 U/mL): May indicate active disease or waning immunity during remission Clinical correlation essential; symptoms and imaging findings crucial for interpretation Repeat testing may be warranted if clinical suspicion remains high
- Declining Titers During Treatment: Suggests response to immunosuppressive therapy May precede clinical improvement Persistently elevated titers despite treatment may indicate inadequate disease control
- Negative Results with Strong Clinical Suspicion: Does not entirely exclude vasculitis; approximately 10% of patients with clinical GPA or MPA may be ANCA-negative Consider alternative diagnoses or repeat testing Tissue biopsy (kidney, lung, skin) may be necessary for confirmation
- Factors Affecting Result Interpretation:
- Stage of Disease: Early disease or early treatment phases show higher positivity Remission Phase: Titers may persist or become negative even with clinical remission Relapse: Rising titers may precede clinical relapse by weeks to months
- Immunosuppressive Therapy: Certain medications (cyclophosphamide, rituximab, mycophenolate) reduce antibody production Testing immediately post-plasmapheresis may show transiently lower titers Serial testing shows trends more useful than single values
- Associated Conditions: Infections, malignancies, and certain medications can produce false-positive low-level ANCA Strong clinical correlation required Persistent positive results favor primary vasculitis diagnosis
Section 4: Associated Organs
- Primary Organ Systems Involved:
- Renal System: Rapidly progressive glomerulonephritis with pauci-immune necrotizing and crescentic GN Primary manifestation in MPA; present in 80-90% of cases GPA affects kidneys in approximately 80% of cases Presents with hematuria, proteinuria, and elevated creatinine Can rapidly progress to end-stage renal disease (ESRD) if untreated
- Pulmonary System: Upper and lower respiratory tract involvement Upper respiratory: Sinusitis, nasal granulomas, epistaxis (GPA more common) Lower respiratory: Nodules, infiltrates, hemoptysis, alveolar hemorrhage Pulmonary-renal syndrome (concurrent pulmonary hemorrhage and glomerulonephritis) Pulmonary involvement occurs in ~90% of GPA and ~50% of MPA
- Nervous System: Both peripheral and central involvement possible Peripheral neuropathy in 20-30% of patients Central nervous system involvement less common but serious Can manifest as mononeuritis multiplex or encephalitis
- Skin: Cutaneous manifestations in 40-60% of ANCA-associated vasculitis Palpable purpura (typically lower extremities and buttocks) Urticarial lesions, nodules, and vesicles Skin biopsy confirms small-vessel vasculitis
- Diseases and Conditions Associated with Abnormal Results:
- Granulomatosis with Polyangiitis (GPA, formerly Wegener's Granulomatosis): PR3-ANCA positive in 85-90% of generalized cases, 50-65% of limited cases Necrotizing granulomas of upper and lower respiratory tract Necrotizing vasculitis of small and medium vessels Glomerulonephritis
- Microscopic Polyangiitis (MPA): MPO-ANCA positive in 50-60% of cases Necrotizing vasculitis of small vessels without granulomas Predilection for kidneys and lungs Pulmonary-renal syndrome most common presentation
- Eosinophilic Granulomatosis with Polyangiitis (EGPA, formerly Churg-Strauss Syndrome): MPO-ANCA positive in 40-50% of cases Characterized by asthma, eosinophilia, and multi-organ vasculitis Includes cutaneous, peripheral nervous system, and cardiac involvement Often preceded by allergic manifestations
- Potential Complications of Abnormal Results:
- Renal Complications: Acute kidney injury progressing to chronic kidney disease End-stage renal disease requiring dialysis or transplantation Permanent renal scarring even after treatment Delayed diagnosis may result in irreversible renal damage
- Pulmonary Complications: Life-threatening alveolar hemorrhage Severe hypoxemia requiring mechanical ventilation Chronic pulmonary fibrosis from recurrent inflammation Increased risk of pulmonary infections
- Neurological Complications: Permanent peripheral nerve damage Stroke risk from CNS vasculitis Mononeuritis multiplex with functional impairment
- Systemic Complications: Mortality 5-10% at one year if untreated Treatment toxicity from long-term immunosuppression Risk of opportunistic infections Secondary malignancies from prolonged immunosuppressive therapy
Section 5: Follow-up Tests
- Additional Tests Recommended Based on Positive ANCA Results:
- Renal Function Assessment: Serum Creatinine: Baseline and periodic measurement to track renal function Blood Urea Nitrogen (BUN): Indicator of renal perfusion and function Estimated Glomerular Filtration Rate (eGFR): Calculated from creatinine for precise assessment 24-hour Urine Protein: Quantifies proteinuria; important for baseline and monitoring Urinalysis with microscopy: Detects hematuria, RBC casts, proteinuria; indicates active glomerulonephritis
- Imaging Studies: Chest X-ray: Assess for pulmonary infiltrates, nodules, or pulmonary hemorrhage High-resolution CT (HRCT) chest: Detect subtle parenchymal disease, bronchiectasis, cavitations Sinus CT: Evaluate extent of sinus disease in GPA Kidney ultrasound or biopsy: Confirmation of vasculitis if diagnostic uncertainty
- Tissue Biopsy: Kidney biopsy with light microscopy, immunofluorescence, and electron microscopy: Definitive diagnosis of necrotizing crescentic GN Skin biopsy: Confirms small-vessel vasculitis Lung or sinus biopsy: May be necessary if diagnosis remains uncertain
- Laboratory Assessment of Disease Activity: Serum Creatinine: Primary marker of renal function status Urinalysis: Detects activity of glomerulonephritis Complete Blood Count: Identifies anemia, thrombocytopenia, infection risk Inflammatory markers (ESR, CRP): Assess systemic inflammation Complement levels (C3, C4): Usually normal in ANCA-AAV; helps exclude other vasculitis types
- Monitoring Frequency and Protocols:
- Induction Phase (First 3-6 months): ANCA testing: At baseline and 1-3 months during initial treatment Renal function: Monthly or bi-weekly monitoring Urinalysis and 24-hour urine protein: Monthly assessment Inflammatory markers (ESR, CRP): Monthly monitoring Complete blood count: Monthly to track cytopenias
- Consolidation Phase (6-18 months): ANCA testing: Every 3-6 months Renal function: Every 3 months Urinalysis: Every 3 months Inflammatory markers: Every 3-6 months Imaging: As clinically indicated (typically annually)
- Maintenance Phase (Beyond 18 months): ANCA testing: Every 6-12 months or if clinical symptoms change Renal function: Every 3-6 months Urinalysis: Every 3-6 months Inflammatory markers: Every 6-12 months Clinical assessment: At least annually
- Related Tests Providing Complementary Information:
- Antinuclear Antibody (ANA) Panel: Excludes other autoimmune conditions (SLE, ANCA overlap syndromes) Usually negative or low titer in primary ANCA-AAV
- Rheumatoid Factor: Helps differentiate from other rheumatologic conditions Particularly useful when ANA is positive (concerning for overlap)
- Cryoglobulins and Anti-GBM: Rule out other types of small-vessel vasculitis Cryoglobulinemia presents similarly but requires different treatment Anti-GBM disease (Goodpasture syndrome) requires distinct therapy
- Immunoglobulin Levels: Baseline assessment; elevated IgE in EGPA Total IgE: Usually elevated in EGPA Specific IgE to allergens: May be elevated in EGPA patients
- B-type Natriuretic Peptide (BNP): Screens for cardiac involvement Important in EGPA which frequently affects the heart
- Peripheral Blood Smear: Evaluates for abnormal cells, eosinophilia Critical for confirming EGPA diagnosis (eosinophilia >1500 cells/μL)
Section 6: Fasting Required?
- Fasting Requirement: NO
- The ANCA by IFA reflex MPO/PR3 Antibodies test does NOT require fasting. Patients may eat and drink normally before testing. No dietary restrictions are necessary.
- Patient Preparation Requirements:
- Specimen Collection: Blood collection: Venipuncture into SST (serum separator tube) or plain red-top tube Volume required: Typically 5-10 mL Timing: Can be drawn at any time of day (no time restrictions) No special preparation needed beyond standard phlebotomy precautions
- Medications - No Special Restrictions:
- Continue Regular Medications: Patients should continue taking all prescribed medications including immunosuppressants (corticosteroids, cyclophosphamide, rituximab, mycophenolate, azathioprine, etc.) Do NOT discontinue medications prior to testing
- No Medication Interactions: ANCA testing is not affected by most medications Immunosuppressive therapy may lower antibody titers (this is expected and clinically relevant) Results must be interpreted in context of current medication regimen
- Important Clinical Timing Considerations:
- Testing Before Treatment Initiation (PREFERRED): Provides most reliable baseline ANCA status Uninfluenced by immunosuppressive medications Important for diagnostic confirmation Establish baseline titer for future comparison
- Timing Considerations: Avoid testing immediately after plasmapheresis: May transiently lower titers due to antibody removal Wait at least 1 week after plasmapheresis for accurate titer assessment Recent infections may cause transient false-positive low-level ANCA Recent vaccinations do not affect testing
- Pre-Collection Instructions for Patients:
- Hydration: Maintain normal hydration to facilitate venipuncture Normal fluid intake is acceptable
- Activity: No special activity restrictions Strenuous exercise immediately before testing is not necessary to avoid
- Notify Laboratory of: Recent plasmapheresis or blood transfusions Active infections or recent infections within 1-2 weeks Recent vaccinations (for documentation purposes) Current immunosuppressive regimen Pregnancy status (if applicable)
- Specimen Handling and Storage:
- Allow blood to clot at room temperature for 30-60 minutes Centrifuge at 1200-1500g for 10 minutes Separate serum and place in sterile tube Store refrigerated at 2-8°C if not processed immediately Ship on ice packs if mailing to reference laboratory Specimens should be processed within 24-48 hours of collection

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