The three dengue tests explained
Dengue diagnosis depends on when you test after symptoms start. Different tests are positive at different times:
| Test | When Positive | What it detects |
|---|---|---|
| NS1 Antigen | Day 1–5 of fever | The dengue virus itself (early detection) |
| IgM Antibody | Day 4–5 onwards | Your body's early immune response |
| IgG Antibody | Day 7+ / past infection | Past dengue infection or secondary infection |
What does a POSITIVE NS1 mean?
POSITIVE NS1 Antigen — Active dengue infection
A positive NS1 antigen test in the first 5 days of fever confirms active dengue virus in your blood. NS1 is the most reliable test early in illness. A negative NS1 after day 5 does not rule out dengue — the virus clears quickly; by then, antibody tests (IgM) become more useful.
What does POSITIVE IgM mean?
POSITIVE IgM Antibody — Recent dengue infection
Positive IgM means your immune system has recently mounted a response to dengue — consistent with a current or very recent (within 3 months) infection. IgM becomes detectable from around day 4–5 and stays elevated for 2–3 months after recovery.
What does POSITIVE IgG mean?
POSITIVE IgG — Past infection or secondary dengue
IgG stays in your blood for life after dengue infection. A positive IgG alone means you had dengue in the past. IgG positive + IgM positive = secondary dengue infection (second time getting dengue). Secondary dengue is more likely to cause dengue haemorrhagic fever — watch for warning signs carefully.
Platelet count in dengue — when is it dangerous?
| Platelet Count | What it means |
|---|---|
| > 1,50,000 | Normal — monitor at home |
| 50,000 – 1,50,000 | Low — daily monitoring needed |
| 20,000 – 50,000 | Very low — hospital admission advised |
| < 20,000 | Critical — platelet transfusion may be needed |
Warning signs — go to hospital immediately if you have:
- Severe abdominal pain or tenderness
- Persistent vomiting (more than 3 times in 24 hours)
- Bleeding from gums, nose or in urine/stools
- Sudden drop in temperature (below 38°C) after days of high fever
- Feeling cold, clammy or confused (shock)