Regarding laboratory investigations in dengue fever in children, all of the following are true EXCEPT:

Explanation

## Laboratory Diagnosis of Dengue in Children ### Correct Answer Rationale **The statement about leukocytosis in secondary dengue with complications is NOT typically true.** In dengue fever, **leukopenia** (WBC <4,000/mm³) is the hallmark hematological finding throughout the illness — including in secondary dengue and complicated cases. Leukocytosis is NOT a recognized feature of secondary dengue per se; it may suggest bacterial superinfection or an alternative diagnosis, but it is not a characteristic finding of dengue with complications. This is the EXCEPT answer. ### Diagnostic Timeline and Lab Markers | Investigation | Timeline & Utility | Notes | |---|---|---| | **NS1 Antigen** | Days 1–5 (peak day 2–3) | Most sensitive in first 3 days; ~95% sensitivity; best for early diagnosis (Park 26e) | | **IgM Antibody** | Appears day 5–6; peaks day 10–14; persists 3–4 months | Gold standard for confirming dengue after acute phase | | **IgG Antibody** | Appears day 6–10; persists years | Indicates past infection; useful for epidemiological surveys | | **PCR/Viral Culture** | Days 1–5 (acute viremia) | Highest sensitivity but not routinely available | ### Why Options A, B, and D Are TRUE **Option A (NS1 antigen, day 1–5):** NS1 antigen is detectable from day 1 and typically declines by day 5–6. It is the most useful marker for early (febrile phase) diagnosis — **TRUE**. **Option B (IgM after day 5, persists 3–4 months):** IgM antibodies appear around day 5–6 of illness and persist for approximately 3–4 months, making them useful for diagnosis in the post-acute phase — **TRUE**. **Option D (AST > ALT in dengue hepatitis):** This is actually a debated point, but the **characteristic pattern in dengue hepatitis is AST > ALT** — unlike typical viral hepatitis (HAV/HBV) where ALT > AST. In dengue, AST elevation is disproportionately higher due to myositis and systemic inflammation in addition to hepatocyte injury. This is well-documented in WHO dengue guidelines and multiple studies (Souza et al., 2004; WHO Dengue Guidelines 2009) — **TRUE as stated**. ### Hematological Findings in Dengue **Key Point:** Leukopenia (WBC <4,000/mm³) is the **consistent** hematological finding in dengue — in both primary and secondary infection, with or without complications. The WHO dengue guidelines (2009) and Park's Textbook of Preventive and Social Medicine (26th ed.) do not list leukocytosis as a feature of secondary dengue with complications. Leukocytosis should prompt consideration of bacterial co-infection rather than being attributed to dengue itself. **High-Yield:** Thrombocytopenia (<100,000/mm³) + hemoconcentration (Hct rise >20%) = plasma leakage = warning sign for dengue shock syndrome (DSS). **Clinical Pearl (AST > ALT in Dengue):** Unlike most acute viral hepatitis where ALT > AST, dengue hepatitis characteristically shows **AST > ALT** due to additional contributions from skeletal muscle injury and systemic inflammation — a classic NEET PG distinguishing point (WHO Dengue Guidelines 2009; Harrison's Principles of Internal Medicine).