Scrub typhus IgM

Bacterial/ Viral

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No Fasting Required

Details

Detects IgM antibodies against Orientia tsutsugamushi, the bacterium responsible for scrub typhus

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Scrub Typhus IgM Test - Comprehensive Medical Guide

Why is it done?
- Detects IgM antibodies specific to Orientia tsutsugamushi, the causative agent of scrub typhus (also known as tsutsugamushi disease)
- Used to diagnose acute scrub typhus infection, particularly in endemic regions of Asia-Pacific, including parts of Japan, Korea, China, Thailand, India, and Indonesia
- Ordered when patients present with fever, headache, myalgia, rash, and eschar (characteristic black necrotic lesion) following mite bite exposure
- Typically performed during acute illness phase, 5-7 days after symptom onset when IgM antibodies are most reliably detectable
- Helps differentiate scrub typhus from other endemic febrile illnesses such as dengue, typhoid, and other rickettsial infections
- Essential for guiding appropriate antibiotic therapy (tetracyclines) and preventing serious complications
Normal Range
- Normal/Negative Result: < 1:40 or < 1:80 dilution (depending on laboratory method); often reported as "Negative" or "Not Detected"
- Unit of Measurement: Titer dilution ratios (IFA/IF method) or antibody index (ELISA method)
- Positive Result: ≥ 1:40 or ≥ 1:80 dilution; reported as "Positive" or with specific titer value indicating IgM antibody presence
- Interpretation of Normal: Absence of IgM antibodies suggests either no scrub typhus infection or very early stage (before antibody formation)
- Interpretation of Abnormal: Positive IgM indicates acute or recent scrub typhus infection, typically appearing 5-10 days after symptom onset
- Higher Titer Values: Generally correlate with active infection but do not indicate disease severity; extremely high titers may persist for weeks to months after recovery
Interpretation
- Positive IgM (≥1:40 or ≥1:80): Indicates active or recent acute scrub typhus infection; patient likely has current infection and should receive antimicrobial therapy
- Negative IgM in First Week: May indicate very early infection (before antibody development); repeat testing after 5-7 days recommended; IgG testing may provide additional confirmation
- Equivocal Results: Results near cutoff value warrant repeat testing or alternative diagnostic methods such as PCR or culture
- IgM Persistence: IgM antibodies can persist for 2-6 months post-infection; presence alone does not indicate current active infection if patient recovered weeks prior
- Clinical Context Critical: Test results must be interpreted alongside clinical presentation (fever, eschar, rash, lymphadenopathy), epidemiological history (endemic area exposure, tick/mite exposure), and symptom timing
- Strain Variation: Cross-reactivity with other Orientia strains possible; may see false positives in patients with other rickettsial infections or prior infections with heterologous strains
- Factors Affecting Results: Timing of sample collection, severity of infection, immunocompromised status, prior treatments, and presence of other concurrent infections may all influence IgM detection
Associated Organs
- Primary Organ Systems Affected: Endothelial cells (blood vessel linings), lungs, heart, brain, kidneys, and skin
- Scrub Typhus-Associated Conditions: Acute fever, generalized lymphadenopathy, maculopapular rash (50-80% of patients), characteristic eschar at mite bite site (40-90% of patients)
- Systemic Complications: Interstitial pneumonia, myocarditis, meningitis, hepatitis, acute kidney injury, disseminated intravascular coagulation (DIC), multi-organ failure if untreated
- Respiratory Involvement: Interstitial pneumonia occurs in 20-40% of cases; may lead to respiratory failure requiring mechanical ventilation
- Cardiovascular Involvement: Myocarditis, arrhythmias, hypotension, shock in severe cases
- Central Nervous System: Meningitis, encephalitis, seizures occur in 5-10% of cases; may cause altered mental status and neurological sequelae
- Hepatorenal Dysfunction: Hepatitis with elevated transaminases, acute kidney injury requiring dialysis in severe cases
- Mortality Risk: Untreated mortality rates reach 30-50%; treated cases have mortality of 1-3% with appropriate antibiotic therapy
Follow-up Tests
- Scrub Typhus IgG: Confirms past infection and seroconversion; helps differentiate recent from remote infection when combined with IgM results
- PCR (Polymerase Chain Reaction): Detects bacterial DNA; useful in first week of illness before antibodies develop; most sensitive in early acute phase
- Blood Culture: Culture in specialized media (cell culture); rarely performed in clinical practice due to technical difficulty and biohazard concerns
- Complete Blood Count (CBC): To assess for thrombocytopenia, anemia, and assess severity; thrombocytopenia common in scrub typhus
- Liver Function Tests (LFTs): AST, ALT, bilirubin, albumin to evaluate hepatic involvement; elevated enzymes expected in most cases
- Renal Function Tests: Creatinine, BUN to assess kidney involvement; critical for monitoring severity and antibiotic dosing adjustments
- Coagulation Profile: PT/INR, aPTT, D-dimer to screen for DIC in severe cases
- Chest X-ray: To assess for interstitial pneumonia and respiratory complications; recommend if respiratory symptoms present
- CSF Analysis (Lumbar Puncture): If meningitis suspected; may show lymphocytic pleocytosis with elevated protein and normal glucose
- Repeat IgM Testing: Recommended 5-7 days after initial negative test if high clinical suspicion remains; seroconversion often occurs by second week
- Related Serological Tests: Dengue, typhoid, and other rickettsial serology if differentiating from endemic co-infections in regional disease epidemiology
Fasting Required?
- Fasting: No
- Patient Preparation: Patient may eat and drink normally; fasting not required for this blood test
- Sample Collection: Venous blood draw into serum separator tube or EDTA tube depending on laboratory protocol; typically 3-5 mL required
- Timing of Collection: Sample should be collected 5-7 days after symptom onset for optimal IgM detection; can be collected any time of day
- Medications: No medication restrictions for this test; continue all regular medications including antibiotics if already initiated for treatment
- Special Instructions: Inform laboratory of endemic exposure history; provide accurate symptom onset date for proper interpretation; store serum at 2-8°C if not processed immediately
- Biosafety Considerations: Laboratory personnel should handle samples with standard precautions; Orientia tsutsugamushi poses laboratory biohazard risk and requires BSL-3 for culture

How our test process works!