Model Answer
0 min readIntroduction
Dengue fever, a mosquito-borne viral illness, is a significant public health concern globally, particularly in tropical and subtropical regions. Characterized by a wide spectrum of clinical manifestations, from asymptomatic infection to severe dengue, its diagnosis and monitoring rely heavily on haematological parameters. Between days 3-7 of illness, patients typically experience the critical phase where plasma leakage can occur. Haematological tests during this period are vital for assessing disease severity, detecting complications like bleeding, and guiding clinical management. Understanding the expected changes in blood counts helps clinicians differentiate dengue from other febrile illnesses and predict potential adverse outcomes.
Haematological Tests for Monitoring Dengue Fever (Days 3-7)
The pathophysiology of dengue involves viral replication, immune activation, and increased vascular permeability. These processes lead to characteristic haematological changes, including thrombocytopenia, leukopenia, and haemoconcentration.
1. Complete Blood Count (CBC)
- Haemoglobin (Hb): Initially normal, may rise due to haemoconcentration (increased Hb concentration) as plasma leaks out of the vasculature.
- Total White Blood Cell Count (TWBC): Typically decreases (leukopenia) during the acute phase. Lymphopenia is common. A rising TWBC can suggest secondary bacterial infection.
- Platelet Count: A hallmark of dengue. Platelet counts usually start declining around day 3-5, reaching their nadir between days 5-7. A rapidly falling platelet count (<10,000/µL) is a warning sign for bleeding.
- Red Blood Cell Count (RBC): May be normal or slightly elevated due to haemoconcentration.
- Haematocrit: Increases due to plasma leakage, indicating haemoconcentration. A rapidly increasing haematocrit is a warning sign.
2. Peripheral Smear Examination
This is crucial for:
- Detecting morphological changes in blood cells.
- Assessing platelet morphology (giant platelets may be present).
- Identifying any evidence of disseminated intravascular coagulation (DIC).
- Ruling out other causes of thrombocytopenia.
3. Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT)
These tests assess the coagulation cascade. Prolongation of PT/aPTT can indicate liver dysfunction or early stages of DIC, although they are usually normal in uncomplicated dengue.
4. Fibrinogen Level
Fibrinogen levels are often normal or slightly decreased in uncomplicated dengue. A significant decrease (<150 mg/dL) suggests consumption due to DIC.
5. Dengue NS1 Antigen Test & IgM/IgG Antibodies
While not strictly haematological, these serological tests are often performed alongside haematological investigations to confirm the diagnosis and assess the stage of infection. NS1 antigen is typically positive during the first few days of illness, while IgM antibodies appear later.
6. Liver Function Tests (LFTs)
Although not a haematological test, LFTs are routinely monitored as dengue can cause mild to moderate liver involvement. Elevated AST and ALT levels are common.
| Test | Normal Range | Dengue Findings (Days 3-7) | Significance |
|---|---|---|---|
| Platelet Count | 150,000 - 400,000/µL | Decreasing, often <100,000/µL | Risk of bleeding |
| Haematocrit | 37-47% (females), 42-52% (males) | Increasing | Plasma leakage, haemoconcentration |
| TWBC | 4,000 - 11,000/µL | Decreasing (Leukopenia) | Immune response, risk of secondary infection |
| Fibrinogen | 200-400 mg/dL | Normal or slightly decreased | DIC (if significantly decreased) |
Conclusion
Monitoring haematological parameters between days 3-7 of uncomplicated dengue fever is crucial for early detection of complications like bleeding and plasma leakage. Serial CBCs, peripheral smears, and coagulation studies provide valuable information for assessing disease severity and guiding appropriate fluid management. Close monitoring of platelet counts and haematocrit is particularly important. A proactive approach to haematological monitoring, combined with clinical assessment, significantly improves patient outcomes in dengue fever.
Answer Length
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