Predictive value of quantitative NS1 antigen, IgM and IgG antibody titres in assessing dengue severity in children

The objectives of the study are to evaluate whether quantitative NS1 antigen and IgM/IgG antibody titres predict clinical severity in paediatric dengue and to determine whether the IgM/IgG ratio reliably differentiates primary from secondary infection. A 1-year cross-sectional study was conducted at a tertiary care centre in South India, enrolling children aged 1 month to 18 years with laboratory-confirmed dengue. Quantitative NS1 antigen, IgM, and IgG titres were measured at point-of-care and correlated with clinical outcomes. Severity indices included bleeding manifestations, third spacing, thrombocytopenia, hepatic and renal involvement, shock, and duration of hospitalization. Statistical analysis was performed using chi-square and Mann-Whitney U tests, with receiver operating characteristic (ROC) and area under the ROC curve (AUROC) analyses using IBM SPSS version 29. High NS1 titres (60-100 and ≥ 100) were significantly associated with bleeding, renal dysfunction, elevated SGOT, haemoconcentration, and thrombocytopenia. IgM titres < 4 correlated strongly with third spacing (82.1%, p = 0.019), while IgG titres ≥ 35 predicted third spacing (75%), thrombocytopenia, and elevated transaminases. An IgM/IgG ratio < 0.85 differentiated secondary dengue with superior sensitivity and specificity compared with higher cutoffs (AUROC 0.793). Infantile dengue demonstrated greater severity, with hypoalbuminemia (62%) and central nervous system involvement (25%), despite lower NS1 detection rates, and showed reversal of the typical SGOT > SGPT pattern.

Quantitative NS1 antigen and IgM/IgG antibody titres provide early severity-predictive information in paediatric dengue. An IgM/IgG ratio < 0.85 reliably identifies secondary infection. Incorporating these markers into routine clinical evaluation may enhance early risk stratification, particularly in resource-limited settings.

• NS1 antigen and IgM/IgG antibody titters are widely used for diagnosis, and IgM/IgG ratio is commonly used to classify primary versus secondary dengue. • Dengue severity is higher in secondary infection and is usually assessed using haemoconcentration, thrombocytopenia, and clinical warning signs which often appear late.

• Quantitative titters-High NS1 and low IgM antibody titres predict paediatric dengue severity early, allowing identification of high-risk children at presentation. • Infants show lower NS1 titters but higher severity; IgG titres in secondary dengue do not correlate with day of illness; an IgM/IgG ratio < 0.85 outperforms higher cutoffs (1.59) in identifying secondary dengue.