FIELD-EVALUATION OF THE QBC TECHNIQUE FOR RAPID DIAGNOSIS OF VIVAX MALARIA

The QBC (quantitative buffy coat) technique was compared with that of the Giemsa-stained thick blood film (GTF) under field conditions in Ju nlian and Mingshan counties, Sichuan, China, for rapid diagnosis of vi vax malaria. Blood samples were collected from 364 volunteer villagers , and each sample was examined with both the QBC and GTF techniques. F or each GTF sample (10 mu l of blood), as many as 300 oil-immersion fi elds were examined; each QBC tube was inspected for up to 5 minutes. T he GTF technique resulted in 86 positive blood samples and 278 negativ e; the QBC technique indicated 89 positive and 275 negative samples. R elative to the results obtained with GTF, the QBC technique had a sens itivity and specificity of 87.2% and 95.0%, respectively; concordance between the tests was 93.1%. The median time-to-positive diagnosis wit h the QBC technique (1.12 min) was 11% of that with GTF. The distribut ion of different developmental stages of Plasmodium vivax parasites wa s also examined in the centrifuged QBC tubes: all stages except schizo nts could be found in the lower part of the platelet zone (the interph ase between the monocyte and platelet layers), especially ring forms.