What this test measures
Lateral-flow immunoassay detecting both IgM (suggests recent acute infection) and IgG (suggests past or convalescent) antibodies against Leptospira interrogans. Results in 15–20 minutes. Useful for initial screening but requires confirmation by MAT (microscopic agglutination test — the WHO gold standard) or PCR (most sensitive in first week of illness) in equivocal cases.
Why it matters
Leptospirosis is a major monsoon-onset zoonosis in India — particularly Kerala, Tamil Nadu, Maharashtra, Gujarat, and coastal Karnataka. Causes severe febrile illness (Weil's disease: jaundice + AKI + haemorrhage), with mortality ~5–15% if treated late. Classic clinical features: high fever, severe myalgia (especially calf muscles), conjunctival suffusion (red eye without discharge), jaundice, oliguria, haemoptysis. Treatment is doxycycline (mild) or IV ceftriaxone / penicillin (severe). Empirical treatment is often started during outbreaks while serology is pending.
How to prepare
No fasting required. Blood, plasma, or serum. Disclose recent water exposure (waterlogged streets, sewage, agricultural / rice field work), recent travel to endemic regions, contact with rodents, and 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 (reactive / non-reactive)[1] | Non-reactive | Non-reactive — recent acute infection unlikely; doesn't rule out early window-period or chronic disease. | Reactive — recent acute leptospirosis likely. Empirical treatment with doxycycline (mild) or IV penicillin / ceftriaxone (severe) is reasonable; confirm with MAT. |
| Anti-Leptospira IgG (reactive / non-reactive)[1] | Non-reactive | Non-reactive — no past or convalescent infection. | Reactive — past or convalescent infection. In acute illness, IgG rises later than IgM; both positive suggests established infection. |
Leptospira IgM/IgG interpretation
| IgM | IgG | Likely stage |
|---|---|---|
| Negative | Negative | No infection or very early window (PCR if early) |
| Positive | Negative | Recent acute infection (1–4 weeks) |
| Positive | Positive | Established acute or recent recovered infection |
| Negative | Positive | Past infection / convalescent / endemic exposure |
Frequently asked questions
When does leptospirosis usually peak in India?
During and after the monsoon (July–November in most states) — flooding exposes people to contaminated water from rodent urine.
Why is the test sometimes negative in early disease?
IgM rises 5–7 days after symptom onset. In the first week, PCR of blood (or urine in second week) is the most sensitive test.
Should I be treated empirically?
In high-prevalence settings during monsoon outbreaks, doxycycline is often started empirically for compatible illness while confirmatory tests are pending — early treatment substantially reduces mortality.
What is the MAT confirmation?
Microscopic agglutination test — the WHO gold standard, performed in reference labs. Detects serogroup-specific antibodies and is essential for outbreak epidemiology.
Can I prevent leptospirosis?
Yes — avoid wading in flood water without boots, control rodents, and prophylactic doxycycline 200 mg weekly may be considered for high-exposure occupations (rice farming, sewage work) during outbreaks.
Is leptospirosis the same as dengue?
No — but both present with fever during monsoon. Calf pain, conjunctival suffusion, jaundice, and renal failure point to lepto. Test both if uncertain.
Related Infectious Disease tests
Tests commonly ordered alongside LEPTOSPIRA RAPID TEST (IGG/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
- NCDC India — Leptospirosis · accessed 2026-05-30T00:00:00.000Z
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