What this test measures
Quantitative ELISA detecting IgM antibodies against Leptospira. Reported as positive / negative / equivocal with an index value. More sensitive than rapid lateral-flow tests, especially in the second week of illness when antibody titres are higher. Still requires confirmation by MAT (Microscopic Agglutination Test) for serogroup identification in outbreak investigation.
Why it matters
In endemic Indian states (Kerala, Tamil Nadu, Maharashtra, Gujarat, Goa, coastal Karnataka, Odisha), leptospirosis is a major monsoon-onset febrile illness with high mortality if untreated. Quantitative IgM ELISA is the preferred clinical lab test where available, supporting clinical suspicion with better accuracy than rapid kits. Early disease (first week) may be missed; consider PCR if very recent onset.
How to prepare
No fasting required. Disclose monsoon-related water exposure, occupational risks (farming, sewage, fishing), travel to endemic regions, contact with rodents, current illness duration.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-Leptospira IgM (index / Panbio units / S/CO ratio)[1][2] | Negative (index < 0.9 or < 9 PU) | Negative — recent leptospirosis unlikely. Window-period testing within 5–7 days of symptom onset may miss early cases; PCR is preferred in first week. | Equivocal: repeat in 1 week. Positive: recent acute or recovering leptospirosis — treat with doxycycline (mild) or IV penicillin / ceftriaxone (severe). |
Leptospira IgM ELISA result interpretation
| Index value | Interpretation | Action |
|---|---|---|
| < 0.9 | Negative | If early disease, consider PCR; otherwise consider alternative diagnoses |
| 0.9 – 1.1 | Equivocal | Repeat in 1 week; pursue clinical workup |
| > 1.1 | Positive | Treat per severity; confirm with MAT if outbreak investigation |
Frequently asked questions
Is quantitative ELISA better than the rapid card test?
Yes, modestly — higher sensitivity and specificity. Both have lower yield in first 5–7 days of illness; PCR is more sensitive then.
When in the illness should I get tested?
IgM ELISA sensitivity is highest after day 5–7 of symptoms. PCR of blood (first week) and urine (second week) are more sensitive in very early disease.
Will it confirm the serogroup?
No — ELISA detects pan-leptospira IgM. MAT (microscopic agglutination test) identifies serogroup, important for epidemiology and vaccine planning.
When should I suspect leptospirosis?
Monsoon season + flood / water exposure + acute febrile illness with myalgia (especially calf), conjunctival suffusion, jaundice, oliguria, or pulmonary haemorrhage. Index of suspicion is highest in Kerala, Tamil Nadu, coastal Maharashtra.
What is the treatment?
Mild: doxycycline 100 mg BD × 7 days. Severe (Weil's disease): IV penicillin G or ceftriaxone, supportive care including dialysis if AKI. Mortality 5–15% even with treatment if late presentation.
Can it cross-react with anything?
Some cross-reactivity with relapsing fever (Borrelia recurrentis) and rarely syphilis (Treponema) — both rare in India. Clinical context guides interpretation.
Related Infectious Disease tests
Tests commonly ordered alongside LEPTOSPIRA-IgM, or that help interpret an unexpected result.
Sources & references
- WHO — Leptospirosis Diagnosis · accessed 2026-05-30T00:00:00.000Z
- CDC — Leptospirosis · accessed 2026-05-30T00:00:00.000Z
- ICMR — Leptospirosis Diagnostic Manual · accessed 2026-05-30T00:00:00.000Z
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