Laboratory

These laboratory findings support the above clinical observations:

• Thrombocytopenia (100 000 cells per mm3 or less)
  
• Haemoconcentration (haematocrit elevated at least 20% above average for age, sex and population).
  

00000000The first two clinical observations, plus one of the laboratory findings (or at least a rising haematocrit), are sufficient to establish a provisional diagnosis of DHF. In monitoring haematocrit, one should bear in mind the possible effects of pre-existing anaemia, severe haemorrhage of early volume-replacement therapy. Moreover, pleural effusion observed on a chest X-ray, or hypoalbuminaemia, can provide supporting evidence of plasma leakage, the distinguishing feature of DHF. For a patient with a provisional diagnosis of DHF, if shock is present, a diagnosis of DSS is supported.

Reportable cases of DHF or DSS
Patients with a provisional diagnosis of DHF or DSS should be reported to the health authorities as cases of DHF or DSS if there is:

• Virological or serological evidence of acute dengue infection, or
• History of exposure in a dengue endemic or epidemic area (during a period of epidemic transmission, or significant levels of endemic transmission, it is unlikely that many cases will have laboratory confirmation).
  

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1 Hypotension is defined to be a systolic pressure <80 mmHg (10.7 kPa) for those less than 5 years of age, or <90 mmHg (12.0 kPa) for those greater than or equal to 5 years of age. Note that narrow pulse pressure is observed early in the course of shock, whereas hypotension is observed later, or in patients who experience severe bleeding.