What Does a Positive Dengue IgG Test Mean?
A positive Dengue IgG test indicates past dengue virus infection and does not require specific treatment, but interpretation depends critically on whether the patient is symptomatic and whether IgM antibodies are also present. 1
Core Interpretation Based on Clinical Context
In Asymptomatic Patients
- Positive IgG alone (without IgM or positive NAAT) indicates past dengue infection, not acute disease. 1, 2
- IgG antibodies persist for months to years after infection, serving as a marker of previous exposure but providing no information about when the infection occurred. 1, 3
- No treatment or further testing is typically needed unless the patient is being evaluated for dengue vaccination eligibility. 4
In Symptomatic Patients
The interpretation changes dramatically based on what other tests show:
- IgG positive + IgM positive = Recent or current dengue infection (either secondary infection or late primary infection). 1, 2
- IgG positive + IgM negative + NS1/NAAT negative = Past infection, not explaining current symptoms. 2
- IgG positive + NS1/NAAT positive = Acute secondary dengue infection. 2
Timing and Antibody Development
- IgG antibodies typically appear around day 5-7 in primary infections and earlier in secondary infections. 3
- In primary dengue infection, IgG is usually not detected until disease day 12 or later, while IgM appears by day 5-6. 5
- In secondary dengue infection, IgG appears much earlier (often by days 4-6) and rises rapidly, while IgM may be absent or appear later. 5
Distinguishing Primary from Secondary Infection
The pattern of IgM and IgG positivity helps differentiate infection type:
- Primary infection pattern: IgM positive + IgG negative (early) or both positive (late, after day 12). 6, 7
- Secondary infection pattern: IgG positive with or without IgM positive (96% of cases show this pattern). 6, 7
- Secondary infections represented 62% of cases in one outbreak analysis, demonstrating that positive IgG often indicates reinfection in endemic areas. 7
Critical Limitation: Cross-Reactivity with Other Flaviviruses
Dengue IgG can cross-react with other flaviviruses including Zika, yellow fever, and Japanese encephalitis, which is a major diagnostic pitfall. 1, 3
- Cross-reactivity with Japanese encephalitis virus occurred in 50% of JE cases tested with dengue IgG rapid tests. 6
- When definitive diagnosis is needed, perform plaque reduction neutralization test (PRNT) to distinguish dengue from other flaviviruses. 1, 2
- PRNT titer ≥10 for dengue with Zika PRNT <10 confirms dengue infection. 8, 1
- PRNT titer ≥10 for both dengue and Zika indicates flavivirus infection but cannot identify the specific virus without clinical and epidemiologic correlation. 8, 1
When to Perform Confirmatory PRNT Testing
PRNT should be considered in these specific scenarios: 1
- Patient is pregnant (timing relative to pregnancy cannot be determined by serology alone)
- Distinguishing dengue from Zika is clinically important
- Results will guide epidemiologic investigation
- Both dengue and Zika IgG are positive
- Definitive diagnosis affects clinical management
Diagnostic Algorithm Based on Symptom Timing
For Symptomatic Patients ≤7 Days from Onset
- Perform dengue NAAT (or NS1 antigen test) plus IgM testing as first-line. 1, 3
- IgG testing at this stage helps identify secondary vs. primary infection but does not confirm acute infection alone. 2
For Symptomatic Patients >7 Days from Onset
- Perform IgM antibody testing as the preferred diagnostic method. 1, 3
- IgG positivity at this stage, combined with positive IgM, suggests recent infection requiring PRNT confirmation. 1
Clinical Significance of Triple Positivity
- Patients who are NS1 positive + IgM positive + IgG positive (triple positive) have significantly higher risk of severe dengue complications. 9
- Triple positive status on admission predicted severe thrombocytopenia on day 5 with 90.7% sensitivity and 83.2% specificity. 9
- This pattern indicates secondary infection with active viral replication and warrants closer clinical monitoring. 9
Common Pitfalls to Avoid
- Never assume acute infection based on positive IgG alone—IgM can persist for months, and IgG persists for years, so timing cannot be determined from serology alone. 8, 1
- Do not interpret positive IgG as ruling out acute infection—it may indicate secondary infection when combined with other positive markers. 2
- Without confirmatory PRNT, positive IgG should be interpreted as "presumptive flavivirus infection" in areas with multiple circulating flaviviruses. 8, 2
- In endemic areas with co-circulating flaviviruses, always integrate epidemiologic data about local transmission patterns when interpreting results. 8, 1