Sensitivity of laser light depolarization analysis for detection of malaria in blood samples

Automated light depolarization analysis could be a useful tool for diagnosing malarial infections. This work discusses the results of a diagnostic efficacy study on 411 samples from patients with suspected malaria infection performed with a Cell-Dyn 4000 analyser. Light dispersed at 90 degrees and depolarized can be used for identifying and counting eosinophils. However, other cell populations with depolarizing capacity occur in malarial samples; these result from leukocytes ingesting haemozoin that is derived from the degradation of the haem group of haemoglobin performed by the parasite. A sensitivity of 72 % and specificity of 98 % were recorded, with positive and negative predictive values of 78 % and 97 %, respectively. Although the sensitivity level of the automated light depolarization analysis is not adequate to replace the existing methods for the diagnosis of parasitic diseases, it could alert clinicians to unsuspected infections by parasites, particularly those from the genus Plasmodium.