Comparison of Quantitative Buffy Coat technique (QBC) with Giemsa-stained thick film (GTF) for diagnosis of malaria

Abstract

The renewed interest in the use of fluorescent microscopy for malaria diagnosis prompted the comparison of Quantitative Buffy Coat technique (QBC) with the old standard Giemsa-stained Thick blood Film (GTF) in Ikeja General Hospital, now Lagos State University Teaching Hospital, in Lagos. Blood samples were collected from 353 patients, each examined with the QBC and GTF techniques. Of these, 68 were positive with GTF, 70 with QBC giving a positive rate of 19.3% and 19.8% respectively. The malaria positive rate was calculated as 19.3% using GTF as the standard. In general, females recorded higher percentages (58.6% and 54.4%) than males (41.4% and 45.6%) among those positive with QBC and GTF respectively. The overall sensitivity rate for QBC was 55.9% and the specificity was 88.8%. The positive and negative predictive values of QBC compared to GTF were 54.3%, 89.4% respectively while the concordance of the two techniques was 82.4%. These values were lower than those reported for QBC in previous studies. The sensitivity of QBC reduced further (33.3%) with samples having low parasite density (< 1000 parasites/ul). QBC test was not able to accurately differentiate between different Plasmodium species but with the GTF, 86.7% of the infected individuals had Plasmodium falciparum, 7.5% had P. malariae and only 5.9% had mixed infections. In spite of the speed and simplicity of QBC technique, it cannot be considered an acceptable alternative to GTF under routine clinical laboratory situation. However, its speed and ease of use make it an important new tool for the diagnosis of malaria.