Comparison of five methods of malaria detection in the outpatient setting

In eastern Africa where 90% of the malaria is due to Plasmodium falciparum, the accuracy of malaria diagnosis at the outpatient level is becoming incr easingly important due to problems of drug resistance and use of alternativ e, costly antimalarial drugs. The quantitative buffy coat (QBC(R)) techniqu e, acridine orange staining with an interference filter system, and the Par aSight(R)-F test have been introduced as alternative methods to conventiona l microscopy for the diagnosis of malaria. Two hundred thirteen outpatients were tested using these alternative methods and conventional microscopy by five experienced technologists; two were randomly allocated to read the re sults of each test. Paired results showed the highest level of agreement wi th the ParaSight(R)-F test (99%), followed by Field stain (92%). The result s of the QBC(R) technique showed the least agreement (73%). Using conventio nal microscopy as the reference standard, the ParaSight(R)-F rest had a sen sitivity range of 90-92% and a specificity of 99%, staining with acridine o range had a sensitivity range of 77-96% and a specificity range of 81-98% a nd the QBC(R) technique had a sensitivity range of 88-98% and a specificity range of 58-90%. All microscopic tests showed lower sensitivities (as low as 20% using staining with acridine orange) in detecting low parasitemias ( less than or equal to 320/mu l) than the ParaSight(R)-F test (70%). Due to the high cost of the ParaSight(R)-F test, Field,stained blood films remain the most appropriate method for diagnosis of P. falciparum in eastern Afric a. The ParaSight(R)-F test may be used in situations where no trained micro scopists are available, or where malaria is strongly suspected and the resu lts of microscopy are negative.