3.1 Lab Tests for Diagnosis and Monitoring

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The management of DS is based on clinical judgment rather than laboratory evaluations alone. However, few indirect tests may be suggestive of DS from the outset. The following tests may be done-

1. Complete Blood Count (CBC)

Including Total Leucocyte Count, Total Platelet Count and HcT should be done on first consultation of the patient to have the baseline:

Recommendations:

  • All febrile patients at the first visit within one week
  • All patients with warning signs.

Leucopenia is common in both adults and children with DF and has an important diagnostic implication in early period. The change in total white cell count (≤5000 cells/mm3) and ratio of neutrophils to lymphocyte (neutrophils <lymphocytes) is useful to predict the critical period of plasma leakage. This finding precedes thrombocytopenia or rising haematocrit. These changes seen in DF and DHF.

Thrombocytopenia is observed in some patients with DF. Mild (100,000 to 150,000 cells/mm3) is common and about half of all DF patients have platelet count below 100,000 cells/mm3; A sudden drop in platelet count to below 100,000 occurs before the onset of shock or subsidence of fever. The level of platelet count is correlated with severity of DHF. Severe thrombocytopenia (<100,000/mm3) usually precedes/accompanies overt plasma leakage.

Haematocrit: A slight increase may be due to high fever, anorexia and vomiting (10%). A sudden rise in haematocrit is observed simultaneously or shortly after the drop in platelet count. Haemoconcentration or rising haematocrit by 20% from the baseline, e.g. from haematocrit of 35% to ≥42% is objective evidence of leakage of plasma. It should be noted that the level of haematocrit may be affected by early volume replacement and by bleeding.

2. Biochemical Tests

Serum AST (SGOT) and ALT (SGPT):

AST and ALT levels are frequently elevated in both adults and children with DF and DHF; AST and ALT Levels are significantly higher (5 to 15 times the upper limit of normal) in patients with DHF. Commonly AST is more than ALT in these cases.

In Special Cases:

  • Hypoproteinemia/Hypoalbuminaemia (as a consequence of plasma leakage).
  • Hyponatremia is frequently observed in DHF and is more severe in shock.
  • Hypocalcemia (corrected for hypoalbuminemia) has been observed in DHF.
  • Metabolic acidosis is frequently found in cases with prolonged shock.
  • Blood urea nitrogen is elevated in prolonged shock.

3. Coagulation Profile

Assays of coagulation and fibrinolytic factors show reduction in DSS cases. Partial thromboplastin time and prothrombin time are prolonged in about half and one third of DHF cases respectively. Thrombin time is also prolonged in severe cases.

4. Other tests

  • Urine R/M/E: Albuminuria
  • Stool test: Occult blood is often found in the stool.
  • Chest X-Ray or Ultrasonography: For detection of pleural effusions or ascites.
  • Other tests for exclusion: Malaria (MP/ICT), Enteric fever (Blood culture) may be required for patients with compatible clinical syndromes.
  • Other test as and when clinically indicated (especially for Dengue expanded syndrome): Serum Albumin, Liver Function Tests, Renal Function test, Serum electrolytes, Imaging, ECG, Echocardiography, CSF etc.

N.B: It should be noted that the use of medications such as analgesics, antipyretics, anti-emetics and antibiotics can interfere with liver function and blood clotting.