Infection Test

Dengue Test (NS1, IgM, IgG)

Name: Dengue Test (NS1, IgM, IgG): What Your Results Mean
Creator: Suman Konda
Published: 2026-07-05

Dengue fever is one of the most common mosquito-borne illnesses in tropical and subtropical regions. Three different blood tests are used to confirm it: here's what each one means.¹

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last reviewed and updated: 01 August 2026 · How we check our content

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
> 150,000	Normal: monitor at home
50,000 – 150,000	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)

References

Sources cited on this page. PubMed links open the original abstract.

Guzman MG, Halstead SB, Artsob H, et al. Dengue: a continuing global threat. Nat Rev Microbiol. 2010;8(12 Suppl):S7–16. PMID 21079655 · doi:10.1038/nrmicro2460

NS1 antigen, IgM, and IgG – three dengue tests and when to use each

Dengue testing uses three distinct markers that are relevant at different stages of infection:

NS1 antigen (non-structural protein 1): The dengue virus produces NS1 protein in large quantities during active replication. NS1 is detectable in blood from day 1 to day 9 of illness – before the immune response fully develops. It is the best test in the first five days. A positive NS1 confirms active dengue infection. Sensitivity is around 80–90% in primary infection but lower in secondary infection (when pre-existing antibodies clear NS1 faster).
Dengue IgM: The immune system begins producing IgM antibodies from day 4–5 of illness, peaking at weeks 2–3 and remaining detectable for 2–3 months. IgM confirms dengue if the patient presents late (after day 5). It can cross-react with Zika virus and other flaviviruses, so a positive result must be interpreted alongside clinical context and travel history.
Dengue IgG: IgG appears slightly later than IgM and remains detectable for years. A rising IgG titre between acute and convalescent samples (taken 2 weeks apart) confirms recent infection. High IgG early in illness indicates secondary dengue – a second dengue infection with a different serotype – which carries significantly higher risk of dengue haemorrhagic fever.

Dengue haemorrhagic fever and the warning signs

Most dengue infections cause a self-limiting flu-like illness (dengue fever): high fever, severe headache, pain behind the eyes, joint and muscle pain ("breakbone fever"), and a rash. However, a minority – especially secondary infections or young children – progress to severe dengue (dengue haemorrhagic fever or dengue shock syndrome), which can be life-threatening.

Warning signs that mandate urgent hospital assessment (WHO criteria):

Abdominal pain or tenderness
Persistent vomiting (inability to keep fluids down)
Clinical fluid accumulation (ascites, pleural effusion)
Mucosal bleeding (nosebleed, gum bleeding, blood in vomit or stool)
Lethargy, restlessness, or rapid deterioration
Liver enlargement above 2 cm
Platelets falling rapidly below 100 × 10⁹/L or haematocrit rising (indicating plasma leakage)

During the critical phase (days 3–7 of illness, when fever may actually break), platelets and haematocrit must be monitored daily – or twice daily in severe cases. Dengue has no specific antiviral treatment; management is supportive with careful fluid balance and close monitoring for haemorrhage.

What full blood count findings suggest dengue

Before NS1 or antibody testing is available, the FBC provides important clues. Characteristic findings in dengue include: leucopenia (low white cell count, often below 4 × 10⁹/L by day 3), thrombocytopenia (low platelets, often falling progressively – a platelet count below 100 is a warning sign; below 20 risks spontaneous bleeding), and a rising haematocrit (concentration of red cells) indicating haemoconcentration from plasma leakage. These FBC changes in a febrile traveller returning from a dengue-endemic region should prompt specific dengue testing immediately.