Usefulness of a centrifuged buffy coat smear examination for diagnosis of malaria

Malaria continues to be a global public health challenge. Microscopic examination of peripheral blood smear (PBS) is the standard method for malaria diagnosis, which is easily available and has low cost but its reliability is questionable at low level of parasitaemia. The present study was undertaken to assess the usefulness of a modified centrifuged buffy coat smear (CBCS) technique for diagnosis of malaria and to compare it with conventional PBS examination and antigen detection test.

The study was carried out over a 6-month period from July to December 2011. Blood samples (2-3 ml per patient) collected in EDTAvials from patients with a clinical suspicion of malaria were subjected to all three tests, that is PBS, CBCS and antigen test and results were compared with antigen test as the gold standard.

Of 1655 samples received, 394 (23.8%) samples were positive for infection with malaria parasites. All the three tests detected malaria infection equally in 279 samples, and gave varied results in the remaining 115 samples. Addition of centrifugation (i.e. CBCS) to the conventional method of PBS enabled detection of 80 more cases of plasmodia infection, especially (43, 53.7%) at low levels of parasitaemia (<200 parasites/μl). While both PBS and CBCS had excellent specificity (99.7% and 99.2%, respectively), PBS examination had low sensitivity (72.9%) in detecting malaria parasites in comparison to CBCS. The sensitivity of CBCS in detecting malaria parasites was 91.9%.

The development of easy, rapid and accurate tests for the reliable detection of plasmodia infection is highly desirable. The CBCS technique fulfils most of these criteria and may be adopted for rapid and reliable diagnosis of malaria in resource-limited settings.