Diagnosis of Dengue virus

The diagnosis of dengue is usually made clinically. The classic picture is high fever with no localising source of infection, a petechial rash with thrombocytopenia and relative leukopenia (low platelet and white blood cell count). Care has to be taken as diagnosis of Dengue Haemorrhagic Fever
can mask end stage liver disease and vice versa. If one has persistent fever for more that 2 days then one should go for a
(CBC). If the platelet count and WBC count are below than their usual range one should go for Dengue Antigen test.
Dengue is always a diagnosis of exclusion, and other diseases with the same initial clinical presentation must be suspected. In order to help the clinician in the detection of severe forms of dengue (DHF/DSS), even when the definitive diagnosis has not been made yet, the following three essential laboratory tests may help in the evaluation of the real clinical conditions of the patient and its early supportive management:

All White Blood Cells Count: In case of dengue, this test will reveal leukopenia. The presence of leukocytosis and neutrophilia excludes the possibility of dengue and bacterial infections (leptospirosis, meningoencephalitis, septicemy, pielonephritis etc.) must be considered.
	Thrombocytopenia (less than 100.000 per mm3): Total platelets count must be obtained in every patient with symptoms suggestive of dengue for three or more days of presentation. Leptospirosis, measles, rubella, meningococcemia and septicemy may also course with thrombocytopenia
	Hematocrit (micro-hematocrit): According to the definition of DHF, it’s necessary the presence of hemoconcentration (hematocrit elevated by more than 20%); when it’s not possible to know the previous value of hematocrit, we must regard as significantly elevated the results more than 45%.