Model Answer
0 min readIntroduction
Dengue fever, a mosquito-borne viral infection, is a significant public health concern globally, particularly in tropical and subtropical regions. Early and accurate diagnosis is crucial for effective clinical management and preventing complications. Diagnosis relies on a combination of clinical presentation and laboratory investigations. The utility of these investigations varies depending on the stage of illness – febrile, critical, and recovery – as the viral load and immune response change over time. Timely diagnosis aids in appropriate patient management and public health interventions.
Investigations for Dengue Fever Diagnosis
The diagnosis of Dengue fever involves a range of investigations, broadly categorized into direct viral detection, serological tests, and hematological assessments. The usefulness of each test varies with the day of illness.
Phase 1: Febrile Phase (Days 1-5)
- NS1 Antigen Detection: This is highly sensitive and specific during the first 5 days of illness, coinciding with viremia. A positive NS1 test confirms acute Dengue infection.
- PCR (Polymerase Chain Reaction): Detects viral RNA directly. Most sensitive in the first few days, but expensive and not widely available.
- Complete Blood Count (CBC): Shows initial thrombocytopenia (low platelet count) and leukopenia (low white blood cell count). These findings are not specific to Dengue but raise suspicion.
Phase 2: Critical Phase (Days 5-10)
This phase is characterized by plasma leakage, leading to potentially life-threatening complications.
- IgM and IgG Antibody Detection: IgM antibodies start appearing around day 5 and peak within 10-14 days. IgG antibodies appear later and provide long-term immunity. IgM positivity confirms recent infection.
- CBC: Thrombocytopenia worsens, and hematocrit (red blood cell concentration) increases due to plasma leakage. Monitoring these parameters is crucial for assessing disease severity.
- Liver Function Tests (LFTs): Elevated transaminases (AST, ALT) indicate liver involvement, common in Dengue.
Phase 3: Recovery Phase (Days 10-14+)
- IgG Antibody Detection: IgG antibodies become dominant, indicating past infection and immunity.
- CBC: Platelet count gradually recovers.
- Dengue IgG ELISA: Used to confirm past infection and assess immunity.
| Investigation | Days 1-5 (Febrile) | Days 5-10 (Critical) | Days 10+ (Recovery) |
|---|---|---|---|
| NS1 Antigen | Highly Positive | Positive, decreasing | Negative |
| PCR | Highly Positive | Positive, decreasing | Negative |
| IgM Antibodies | Negative/Early Positive | Positive, peaking | Positive, declining |
| IgG Antibodies | Negative | Positive, rising | Positive, dominant |
| CBC | Thrombocytopenia, Leukopenia | Worsening Thrombocytopenia, Increased Hematocrit | Platelet recovery |
Limitations: Cross-reactivity with other flaviviruses (e.g., Zika, Chikungunya) can occur in serological tests. False negatives are possible with PCR if the viral load is low. Clinical correlation is always essential.
Conclusion
Diagnosing Dengue fever requires a strategic approach utilizing a combination of investigations tailored to the stage of illness. NS1 antigen and PCR are most useful in the early febrile phase, while serological tests (IgM and IgG) become crucial during the critical and recovery phases. Hematological parameters, particularly platelet count and hematocrit, are vital for monitoring disease severity. Accurate diagnosis, coupled with appropriate clinical management, is essential for reducing morbidity and mortality associated with Dengue fever.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.