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

UNLABELLED: 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.

CONCLUSION: 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.

WHAT IS KNOWN: • 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.

WHAT IS NEW: • 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.