Weil Felix

Bacterial/ Viral

Report in 48Hrs

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No Fasting Required

Details

Serological agglutination test used historically to aid in the diagnosis of rickettsial infections

₹1,050₹1,350

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Weil Felix Test Information Guide

Why is it done?
- The Weil Felix test is a heterophile agglutination test used to detect antibodies against Rickettsia species, which are the causative agents of rickettsial infections
- Primarily ordered to diagnose spotted fever group rickettsiae (such as Rocky Mountain spotted fever) and typhus group rickettsiae infections
- Used as a rapid, presumptive screening test for patients presenting with fever, rash, and history of tick exposure or louse exposure
- Typically performed during acute phase of illness, ideally 7-10 days after symptom onset when antibody titers are most reliable
- Employed in resource-limited settings where more specific rickettsial serologies may not be readily available
Normal Range
- Negative/Normal Result: Weil Felix reaction is negative (no agglutination observed) or titer is ≤1:80
- Unit of Measurement: Reciprocal titer expressed as ratios (1:40, 1:80, 1:160, 1:320, 1:640, 1:1280, and higher)
- Positive Result: Titer ≥1:80 to 1:160 or higher; indicates recent or current rickettsial infection
- Borderline Results: Titers between 1:40 and 1:80 require clinical correlation and may necessitate repeat testing
- Low Positive: A single titer of 1:160 is considered presumptive for rickettsial infection; a fourfold rise in paired sera is highly suggestive
- Normal interpretation implies absence of detectable Rickettsia antibodies; patient's Proteus agglutinins (used in this cross-reactive test) are at baseline levels
Interpretation
- Negative Result (Titer <1:80): Rickettsial infection is unlikely; however, early in disease course (first week) negative results do not exclude infection
- Weakly Positive (Titer 1:80-1:160): Suggestive of rickettsial infection, particularly when clinical presentation is compatible; should be correlated with patient symptoms and epidemiologic data
- Moderately Positive (Titer 1:320-1:640): Consistent with active rickettsial infection; combined with clinical findings, supports diagnosis of spotted fever or typhus
- Highly Positive (Titer ≥1:1280): Indicates significant antibody response, suggestive of recent or current rickettsial infection; confirms suspected diagnosis
- Paired Acute and Convalescent Sera: A fourfold or greater rise in titer between acute phase (first week) and convalescent phase (2-3 weeks) confirms rickettsial infection
- Important Limitations: Test is non-specific; cross-reactivity exists between different Rickettsia species; cannot differentiate between spotted fever group and typhus group infections; false positives may occur in patients with other bacterial infections
- Timing Factors: Results depend on stage of illness; early in disease (first 5-7 days), antibodies may not yet be detectable; titers peak at 3-4 weeks and remain elevated for months to years
- Clinical Context Essential: Result interpretation must incorporate clinical presentation, geographic location, seasonal variation, exposure history (ticks, lice), and presence of characteristic rash
Associated Organs
- Primary Systems: The test identifies infections affecting multiple organ systems; rickettsiae primarily infect vascular endothelial cells throughout the body
- Cardiovascular System: Rickettsiae cause vasculitis; abnormal results may indicate myocarditis, pericarditis, or endocarditis complications from rickettsial infection
- Central Nervous System: Positive results may indicate rickettsial meningitis or encephalitis; can lead to altered mental status, headache, and neurological complications
- Respiratory System: Abnormal test results may correlate with interstitial pneumonitis or acute respiratory distress syndrome (ARDS) from rickettsial infection
- Skin and Soft Tissues: Positive test results are associated with petechial and maculopapular rashes characteristic of rickettsial infections
- Kidney and Renal System: Abnormal results may indicate acute kidney injury (AKI) or glomerulonephritis from rickettsial vasculitis
- Immune System: Positive test reflects antibody production in response to Rickettsia infection; indicates systemic immune activation
- Associated Diseases: Rocky Mountain spotted fever, typhus fever (epidemic, endemic murine, and scrub typhus), Q fever in some cases
- Potential Complications if Untreated: Septic shock, multi-organ failure, disseminated intravascular coagulation (DIC), death if antibiotics not administered promptly
Follow-up Tests
- Specific Rickettsial Serology: Immunofluorescence antibody (IFA) testing against specific Rickettsia species (R. rickettsii, R. typhi, O. tsutsugamushi) for definitive identification and species differentiation
- Paired Acute and Convalescent Sera: Second serum sample drawn 2-3 weeks after initial test to demonstrate seroconversion or fourfold rise in titer, confirming diagnosis
- PCR Testing: Polymerase chain reaction (PCR) for Rickettsia DNA detection from blood or tissue specimens, particularly useful in early disease when antibodies not yet present
- Blood Culture: May be attempted but Rickettsia are slow-growing and difficult to culture; rarely performed in clinical practice
- Complete Blood Count (CBC): Evaluate for thrombocytopenia, leukopenia, or other hematologic abnormalities associated with rickettsial infection
- Coagulation Panel (PT/INR, aPTT): Assess for disseminated intravascular coagulation (DIC) in severe rickettsial infection
- Liver Function Tests (LFTs): Evaluate hepatic involvement; elevated transaminases are common in rickettsial infections
- Renal Function Tests (Creatinine, BUN): Monitor for acute kidney injury secondary to rickettsial vasculitis
- Imaging Studies: Chest X-ray if respiratory involvement suspected; CT scan if neurological complications present
- Lumbar Puncture (CSF Analysis): If meningitis or encephalitis suspected; assess CSF cell counts, protein, glucose, and culture
- Monitoring Frequency: If positive, monitor response to antibiotic therapy; clinical improvement expected within 24-48 hours of doxycycline initiation; repeat serology not routinely needed for treatment assessment
Fasting Required?
- Fasting Required: No
- Food and Beverage: Patient may eat and drink normally; no dietary restrictions are necessary before blood collection
- Medications: No medications need to be withheld; continue all routine medications as prescribed
- Antibiotic Therapy: If already on doxycycline or other rickettsial therapy, testing can proceed; treatment should not be delayed pending test results as mortality increases without prompt antibiotics
- Specimen Collection: Simple venipuncture procedure; a single 5-7 mL serum sample is typically required; can be collected at any time of day
- Patient Preparation: No special preparation needed; patient should be in stable condition for blood draw; continue routine daily activities
- Specimen Handling: Serum should be separated and stored appropriately; can be refrigerated if not tested immediately; repeated freezing and thawing should be avoided
- Timing Recommendation: Optimal timing is 7-10 days after symptom onset for best antibody detection; earlier testing may yield false negatives

How our test process works!