What does an IgM (Immunoglobulin M) negative and IgG (Immunoglobulin G) positive dengue test result indicate?

IgM Negative and IgG Positive Dengue Test Interpretation

An IgM negative and IgG positive dengue test indicates a past dengue infection, not a current acute infection. 1, 2

Understanding the Antibody Pattern

This serological pattern (IgM-/IgG+) has a specific meaning in the timeline of dengue infection:

• IgG antibodies persist for months to years after dengue infection, serving as markers of previous exposure rather than acute disease 1, 2
• IgM antibodies typically appear 3-5 days after symptom onset and can remain detectable for several months, but their absence with positive IgG suggests the acute phase has passed 1
• In primary dengue infections, IgG develops around day 5-7, while in secondary infections it appears even earlier due to immune memory 1

Clinical Interpretation Algorithm

Most Likely Scenario

The IgM-/IgG+ pattern indicates:

• Past dengue infection (most common interpretation) - the patient was infected weeks, months, or even years ago 1, 2
• The patient is not currently in the acute phase of dengue infection 2
• This represents resolved infection with persistent immunity 2

When This Pattern Can Be Misleading

• Cross-reactivity with other flaviviruses (Zika, yellow fever, Japanese encephalitis) can cause false-positive IgG results 2
• Without confirmatory PRNT testing, this should be interpreted as "presumptive flavivirus infection" rather than definitive dengue 2

Required Next Steps Based on Clinical Context

If Patient is Currently Symptomatic

This pattern does NOT explain current symptoms - you must pursue alternative diagnoses:

• Consider other arboviruses (Zika, chikungunya) with concurrent testing 3
• Rule out malaria with thick and thin blood smears in endemic areas 3
• Evaluate for other febrile illnesses based on epidemiologic exposure 3

If Confirmatory Testing is Needed

The CDC recommends:

• Perform PRNT testing against dengue and other endemic flaviviruses for definitive diagnosis 4, 1
• PRNT titer ≥10 for dengue with <10 for other flaviviruses confirms past dengue infection 4
• PRNT titer ≥10 for multiple flaviviruses indicates flavivirus exposure but cannot specify which virus 4

Critical Pitfalls to Avoid

Do Not Assume Acute Infection

• IgG positivity alone cannot determine timing of infection - it may represent infection from years ago 2
• The absence of IgM strongly argues against acute infection, as IgM should be present during active disease (except in very early infection <3-5 days) 1

Do Not Overlook Current Illness

• If the patient has fever now, this IgM-/IgG+ pattern indicates their current symptoms are NOT due to dengue 3
• Aggressively pursue alternative diagnoses rather than attributing symptoms to the positive IgG 3

Consider Cross-Reactivity

• In areas with multiple circulating flaviviruses, integrate epidemiologic data about local virus circulation 4
• Previous flavivirus vaccination or infection can cause positive IgG without recent dengue exposure 2

Special Populations

Pregnant Women

• The interpretation remains the same - IgM-/IgG+ indicates past infection, timing cannot be determined 4
• If symptomatic, pursue concurrent Zika testing with NAAT on both serum and urine 3
• Past dengue infection does not explain current pregnancy complications - investigate other causes 3

Secondary Infection Risk

• Positive IgG indicates the patient has had at least one prior dengue infection 5, 6
• Future dengue infections carry higher risk of severe disease due to antibody-dependent enhancement 5
• Counsel patients about warning signs for severe dengue if they develop febrile illness in the future 5