Haemoconcentration in diagnosing dengue haemorrhagic fever: evidence from a rural Sri Lankan observational study.

Background: One of the World Health Organization criteria for dengue haemorrhagic fever (DHF) is a 20% increase in haematocrit. This study on dengue hospitalised patients compares haematocrit levels at baseline, at the onset of the critical phase and the maximum during the critical phase in rural Sri Lanka.

Methods: This observational study included patients with dengue in the febrile phase who progressed to the critical phase. Haematocrit was recorded and ultrasound scans were performed thrice daily when the platelet count dropped to <100 000/μl. The onset of the critical phase was confirmed by ultrasound-detected plasma leakage.

Results: Forty-three patients were included in the final analysis. The mean haematocrit at baseline and at the onset of the critical phase was 40.6% (standard deviation [SD] 4.7) and 41.3% (SD 5.1), respectively, with no difference (p=0.14, paired t-test). None of the participants showed a 20% increase in haematocrit at the onset of the critical phase, with the maximum observed increase being 17.0%.

Conclusion: A 20% increase in haematocrit was not observed during the critical phase, suggesting that haemoconcentration is unreliable for diagnosing DHF in hospitalised patients. This study recommends revisiting the WHO criterion of a 20% haematocrit increase for diagnosing plasma leakage in dengue patients. It suggests that frequent ultrasound scans may be a more reliable method for early detection of plasma leakage.