Rapid Diagnosis of Bancroftian Filariasis by Acridine Orange Staining of Centrifuged Parasites

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  • Division of Geographic Medicine, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama
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A rapid diagnostic test for detection of microfilaremia using a microhematocrit tube precoated with acridine orange (the Quantitative Buffy Coat [QBC® tube) was compared with a conventional 50 µl-thick blood film (TF) in 119 volunteers in an area of Recife, Brazil that was endemic for Wuchereria bancrofti. Both the QBC and the TF techniques were 100% specific, and thus positive predictive values were equal at 100% for each technique in all subjects studied. Both techniques had equal negative predictive values of 100% in subjects with microfilarial counts > 100 per milliliter (mf/ml). Counts < 20 mf/ml are below a cutoff equal to the calculated limit of sensitivity of each of the two techniques. For those individuals with counts between 20 and 99 mf/ml, negative predictive values were, for practical diagnostic purposes, equivalent at 97.5% for the QBC technique and 99.0% for the TF. Because the QBC technique has predictive values as high as conventional TF, the convenience and rapidity of the technique will make the QBC technique a desirable alternative diagnostic method in those clinical settings where the equipment is available. A positive result will be available in less than six min after obtaining the specimen in individuals with counts < 100 mf/ml, and individuals with lower or no microfilaremia will have a result within 6–12 min.