Practical uses of acridine orange fluorescence microscopy of centrifuged blood (QBC Malaria Test) and the QBCII Hematology System in patients attending malaria clinics in Thailand.

We evaluated the detection of malaria parasites using acridine orange fluorescence microscopy of centrifuged blood (AOFM/CB or "QBC Malaria Test") at two government malaria clinics in rural Thailand. In a subgroup of the patients, a QBC Hematology System for the determination of complete blood counts was also utilized. A Giemsa-stained thick smear (GTS) reading of 100 (1,000x) microscopic fields was used as standard. The AOFM/CB sensitivities were 97% overall and 95% for P. falciparum (Pf). Sensitivity was lower for P. vivax (Pv) (76%). Pv sensitivity depended largely on ameboid form density. A threshold for AOFM/CB to consistently detect Pv ameboid forms was estimated to be 10/100 WBC (700/microliters blood). AOFM/CB was capable of detecting Pf gametocytes and schizonts more frequently than GTS. The total Pf rings per microliter blood estimated from GTS was highly correlated with the number of Pf rings per Paralens microscopic field (PMF) suggesting that AOFM/CB could be used quantitatively. From a technical standpoint, the rural tropical settings of Thailand in this study were not an obstacle to the use of QBC Hematology. The system was found to be useful in conjunction with AOFM/CB. However, in patients heavily infected with Pf gametocytes of Pv ameboid forms, their total WBC and lymphocyte counts needed to be appropriately corrected. Overall, AOFM/CB appears to be a promising tool for field diagnosis of malaria if it is affordable to developing countries.