Thick blood film examination for <it>Plasmodium falciparum </it>malaria has reduced sensitivity and underestimates parasite density

• Main Authors: Gilbert Sarah C, Sanderson Frances, Hunt-Cooke Angela, Andrews Laura, Bejon Philip, Hill Adrian VS
• Format: Article
• Language: English
• Published: BMC 2006-11-01
• Series: Malaria Journal
• Online Access: http://www.malariajournal.com/content/5/1/104

<p>Abstract</p> <p>Background</p> <p>Thick blood films are routinely used to diagnose <it>Plasmodium falciparum </it>malaria. Here, they were used to diagnose volunteers exposed to experimental malaria challenge.</p> <p>Methods</p> <p>The frequency with which blood films were positive at given parasite densities measured by PCR were analysed. The poisson distribution was used to calculate the theoretical likelihood of diagnosis. Further <it>in vitro </it>studies used serial dilutions to prepare thick films from malaria cultures at known parasitaemia.</p> <p>Results</p> <p>Even in expert hands, thick blood films were considerably less sensitive than might have been expected from the parasite numbers measured by quantitative PCR. <it>In vitro </it>work showed that thick films prepared from malaria cultures at known parasitaemia consistently underestimated parasite densities.</p> <p>Conclusion</p> <p>It appears large numbers of parasites are lost during staining. This limits their sensitivity, and leads to erroneous estimates of parasite density.</p>