What this test measures
Dengue Spot is a rapid lateral-flow card test that typically detects either dengue NS1 antigen alone or a combined NS1 + IgM + IgG panel. The result is read visually in 15–20 minutes.
- NS1 antigen is the secreted dengue protein detectable in blood from day 1 to day 7 of fever. - IgM antibody appears from day 4–5 of fever and persists for 2–3 months. - IgG antibody appears from day 7–10 in primary infection (slower) and earlier and higher in secondary infection.
Why it matters
Dengue is endemic across India and causes large monsoon-season epidemics in Mumbai, Thane, Delhi, Bengaluru, Chennai, and most other major cities. The dengue spot test is widely used in OPDs, fever clinics, and outbreak camps for same-day triage, especially because the timing of presentation determines which marker (NS1, IgM, IgG) will be positive.
NS1 + IgM combination has the highest yield in clinical practice — NS1 covers day 1–7, IgM covers day 5–28. NCDC and ICMR recommend confirmation by NS1 ELISA (NIV-validated MAC-ELISA for IgM) for outbreak surveillance and atypical/severe cases. Early dengue diagnosis enables fluid management, platelet monitoring, and warning-sign vigilance for dengue haemorrhagic fever and shock syndrome.
How to prepare
No fasting required. The test uses serum, plasma or whole blood. Mention day of fever onset and any prior dengue history.
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 |
|---|---|---|---|
| Dengue NS1 Antigen (Reactive / Non-reactive)[1] | Non-reactive (Negative) | Non-reactive — no detectable NS1. After day 7, NS1 sensitivity drops; rely on IgM instead. | Reactive — confirmed acute dengue infection (days 1–7). Monitor for warning signs and watch platelet trend. |
| Dengue IgM (Reactive / Non-reactive)[1] | Non-reactive (Negative) | Non-reactive — no recent dengue antibody. If fever started < 5 days ago, IgM may be too early. | Reactive — recent dengue infection (day 5 onward). Lasts 2–3 months. |
| Dengue IgG (Reactive / Non-reactive)[1] | Reactive in past infection | Non-reactive — no past dengue exposure. | Reactive — past dengue infection, or secondary infection (rapid rise). Secondary infection carries higher risk of severe dengue. |
Dengue serology — timing and interpretation
| Day of fever | NS1 | IgM | IgG | Interpretation |
|---|---|---|---|---|
| Day 1–4 | Positive | Negative | Negative | Early primary acute dengue. |
| Day 5–7 | Positive | Positive | Negative | Acute primary dengue. |
| Day 5–7 | Positive | Positive | Positive (high) | Secondary dengue — higher severe-dengue risk. |
| Day 7–14 | Negative | Positive | Negative | Convalescent primary dengue. |
| Months later | Negative | Negative | Positive | Past dengue infection. |
Frequently asked questions
My NS1 is positive but IgM is negative. Is that normal?
Yes — in early dengue (days 1–4), NS1 is positive before IgM develops. This is a typical early acute dengue pattern.
My IgG is high during this fever — what does that mean?
High early IgG with positive NS1/IgM suggests secondary dengue (you have had dengue before). Secondary infection carries higher risk of dengue haemorrhagic fever and dengue shock syndrome — monitor closely.
How long does dengue IgM stay positive?
Typically 2–3 months. A positive IgM does not always mean current fever is from dengue — clinical correlation matters.
Why is platelet count important in dengue?
Platelets typically fall between days 3–7 of dengue. A platelet drop below 100,000 needs daily monitoring; below 20,000 carries bleeding risk and may need hospital admission.
Should I take paracetamol or other painkillers?
Paracetamol only. Avoid aspirin, ibuprofen, and other NSAIDs — they worsen bleeding risk in dengue.
Is there a vaccine for dengue?
A vaccine (Qdenga, CYD-TDV) is approved internationally but currently has limited availability and indication in India. Prevention focuses on Aedes mosquito control.
My family member has dengue — can I catch it from them?
Not directly. Dengue spreads only through Aedes mosquito bites. The household is at risk from the same mosquitoes — eliminate stagnant water and use repellents.
Related Infectious Disease tests
Tests commonly ordered alongside DENGU SPOT, or that help interpret an unexpected result.
Sources & references
- NIV Pune — Dengue Research and Diagnosis · accessed 2026-05-30T00:00:00.000Z
- NCDC India — National Vector Borne Disease Control Programme · accessed 2026-05-30T00:00:00.000Z
- WHO — Dengue Fact Sheet · accessed 2026-05-30T00:00:00.000Z
- ICMR India — Dengue Guidelines · accessed 2026-05-30T00:00:00.000Z
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