[Diagnosis of malaria by allele-specific PCR]

Malaria is relatively rare in Japan. Of 13 patients referred to our laboratory for malarial screening in the past 4 years, malarial parasites were detected in 8. Conventional screening procedures commonly detect hepatic dysfunction, thrombocytopenia, elevated LDH activity, and increased CRP levels in malaria patients. More notably, the 8 malaria patients identified by our laboratory also demonstrated reactive lymphocytosis. In the absence of additional clinical information, reactive lymphocytosis alone may be enough to warrant laboratory blood smear tests on the suspicion of malaria. Conventional microscopic methods have often proved inconclusive in identifying malarial parasite species or detecting mixed infections. However, by combining the methods of DNA analysis with those of microscopy, we were able to conclusively diagnose all cases of suspected malaria. As a test of their skills, 9 laboratory technicians relatively inexperienced with malarial parasites were asked to screen 6 samples: 3 containing malarial parasites, and 3 that were malaria-free. Although none of the technicians were able to accurately identify the samples without additional clinical information, 4 accurately identified all malarial samples when that information was provided. Experience is a crucial determinant of ability to detect malarial parasites by microscopic methods alone. Nonetheless, the findings of our study suggested the diagnostic accuracy of laboratory screening procedures for malaria can be significantly improved if combined with minimal clinical data and the techniques of DNA analysis.