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Blood Test Tracker

Dengue virus IgM

A blood test for IgM antibodies against the dengue virus, used to look for a recent dengue infection.

AI-verified against cited sources. Awaiting expert reviewAlso called DENV IgM, Dengue IgMLOINC 23992-1

What it is

Dengue is a virus spread by the bite of infected Aedes mosquitoes. IgM is the first type of antibody your body makes when it meets a new germ. This test checks your blood for IgM that reacts with dengue virus. Many labs report it as negative, equivocal or positive. Some also print a number called an index. The test cannot tell which of the four dengue virus types you were exposed to.

Why it matters

Dengue can look like many other fevers. Most people with dengue have mild symptoms or none, but a small share develop severe dengue, which needs urgent care. A clinician may use this test, along with your symptoms and travel history, to help work out whether a recent illness was dengue. It works best after the first few days of illness. Early in the illness, tests that look for the virus itself (NS1 antigen or PCR) are usually done too, because IgM can still be negative.

If it’s high

A positive IgM means your blood has antibodies that react with dengue virus. The CDC calls a single positive IgM a presumptive recent dengue infection, not a final answer. Related viruses can cause the same result, so your clinician will read it along with your symptoms, where you have been, and other tests.

Common causes

  • Recent dengue infection
  • A cross-reaction with another related virus, such as Zika, West Nile or yellow fever, or with a past infection from one of them
  • A second dengue infection with a different dengue virus type, which can trigger a new IgM response

What can help

  • Tell your clinician the date your symptoms began and where you have traveled
  • Ask whether a second test (virus tests such as NS1 antigen or PCR, or a neutralization test) would help confirm the result
  • Ask your clinician about rest and fluids, and know the warning signs listed under 'When to seek care'

What can affect your result

  • Timing: IgM can still be negative in the first days of illness
  • Past or current infection with related viruses (Zika, West Nile, yellow fever) can cause a false-looking positive
  • The lab's kit and cut-offs: Quest calls an index of 1.65 or lower negative, 1.66 to 2.83 equivocal and 2.84 or higher positive, while ARUP uses 1.64 or lower, 1.65 to 2.84 and 2.85 or higher
  • Timing: IgM usually shows up during the first week of illness, so a sample drawn in the first few days can be negative even when dengue is the cause. Quest and the CDC give different day counts for when IgM is reliable.
  • Cross-reaction: antibodies to related viruses (flaviviruses such as Zika, West Nile and yellow fever) can make this test read positive. A past infection with one of these viruses can also do it.
  • Labs use different kits and cut-offs. Index values from one lab cannot be compared with another lab's.

IgM usually becomes measurable during the first week of illness (CDC: after day 3 for most infections; Quest: after day 6). It can stay positive for about 3 months (CDC) or several months (Quest), and ARUP notes that low levels may occasionally persist for more than 12 months.

When to talk to a clinician

A positive IgM does not by itself mean you need emergency care, but dengue can worsen as the fever goes away. Get urgent medical care if you or someone you care for has belly pain or tenderness, vomiting at least 3 times in 24 hours, bleeding from the nose or gums, vomit or stool with blood, or extreme tiredness or restlessness. These signs often appear 24 to 48 hours after the fever drops. If you cannot reach a clinician or feel very unwell, call 911 or your local emergency number.

Questions you could ask

  • Was my sample drawn early enough for this test to be reliable?
  • Should we repeat the test later in the illness?
  • Could this result be a cross-reaction with another virus such as Zika?
  • Should we run a confirmatory test, such as an NS1 antigen test, PCR or a neutralization test?
  • Which warning signs should I watch for, and when should I call you?

Questions people ask

Does a positive dengue IgM mean I definitely had dengue?

Not for certain. The CDC treats a single positive IgM as a presumptive recent infection. Other related viruses, including Zika and West Nile virus, can cause a positive result. Your clinician will look at your symptoms, travel and other tests.

My IgM was negative but I have a fever. Can it still be dengue?

Yes, if the sample was drawn early. IgM usually appears during the first week of illness. In the first days, clinicians also use tests that look for the virus itself (NS1 antigen or PCR). A later sample can be checked if the first one was early.

How long does dengue IgM stay positive?

The CDC says IgM can be detected for about 3 months. Quest says a positive IgM may persist for several months, and ARUP notes that low levels may occasionally persist for more than 12 months. So a positive result can reflect an infection from some weeks or months ago.

Show the science and sources

For clinicians and researchers

Dengue IgM is measured by enzyme immunoassay (Quest: EIA; ARUP: semi-quantitative ELISA) and reported as an index value. It is not serotype-specific, because the assay detects IgM against all four dengue virus serotypes, and a new IgM response can follow exposure to a second serotype (Quest). Per the CDC, IgM testing can identify most recent infections after day 3 of illness and IgM can be detected for approximately 3 months, with detection becoming less reliable as levels fall. Quest states IgM is usually detectable after the sixth day of symptoms, that before day 6 both IgM and IgG may be negative so NS1 antigen or NAAT is recommended early, and that a positive IgM may persist for several months. ARUP notes that low levels of IgM may occasionally persist for more than 12 months. In the acute phase (0 to 7 days after symptom onset) the CDC recommends a NAAT plus an IgM test, or an NS1 antigen test plus an IgM test, and after day 7 it recommends IgM as the primary test. A single positive IgM is classed as a presumptive recent infection, and a change from negative to positive IgM in paired samples (the first taken in the first 7 days of illness, the second after symptoms subside) classifies the infection as recent. Cross-reactivity with other flaviviruses (Zika, West Nile, yellow fever, Japanese encephalitis and St. Louis encephalitis viruses) is a recognized limitation. Plaque reduction neutralization testing (PRNT) can help distinguish them but does not always give a conclusive result, particularly in people exposed to several flaviviruses. Cut-offs differ by lab: Quest reports an index of 1.65 or lower as not detected, 1.66 to 2.83 equivocal and 2.84 or higher detected; ARUP reports 1.64 or lower negative, 1.65 to 2.84 equivocal (repeat testing in 10 to 14 days may help) and 2.85 or higher positive. Both labs report the result under LOINC 23992-1 (units/volume, by immunoassay); other LOINC codes exist for presence and titer reporting.

LOINC 23992-1 (primary), 25338-5, 29663-2, 23968-1, 6812-2. Specimen: serum.

Sources

  1. Clinical Testing Guidance for Dengue, US Centers for Disease Control and Prevention
  2. Symptoms of Dengue and Testing, US Centers for Disease Control and Prevention
  3. Dengue, World Health Organization (2025)
  4. Dengue Fever Antibody (IgM) (test code 37580), Quest Diagnostics
  5. Dengue Fever Virus Antibody, IgM (test 0093098), ARUP Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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