Malaria Screening of Blood Donors

Abstract

, describing their findings comparing malaria antibody and antigen tests as screening tests for malaria carriership among blood donors. The authors advocate the use of antigen testing over antibody because, according to their findings, the antibody test would have resulted in exclusion of 7.6% of donations, whereas the antigen test would necessitate the exclusion of only 0.17% of donations.Interesting as these findings are we would like to record our experience using the antibody test alone as the method of screening donations for potential infectivity with malaria. Agreeing with Saeed et al that up-front microscopic examination of blood smears is not cost-effective for detecting malaria in asymptomatic individuals, we have adopted, as an alternative to the Saudi Arabian Ministry of Health (MOH) directives for microscopic screening for malaria, antibody screening using an enzyme-linked immunoassay (ELISA) kit identical to that used by Saeed and his colleagues 1 . In our case, we use an automated robotics platform. Following the manufacturer's direction, serum samples registering an optical absorption above 0.400 are deemed positive, which, if repeated on a second run are then classified as reactive for malaria antibody. In our protocol, we submit every reactive donation sample to supplemental microscopic examination of a thick blood film (TBF) and thin blood smear (TBS) prepared according to standard methods. Only if these examinations are positive for malaria, would we consider the donation infective and not suitable for use. This supplemental testing procedure was adopted because TBF (and TBS) examination remains the (albeit imperfect) reference method for diagnosing or detecting malaria in blood, and we reason that the majority of immunologically competent persons infected with malaria will continue to produce antibody, in which case, detection of parasites by microscopy should be uncomplicated and straightforward and must be done to confirm infection.In the course of 2 years, approximately 44 907 donations were tested using the above protocol. Only 291 (0.65%) of these were reactive, and up to quite recently, in none of these 291 were we able to demonstrate TBF or TBS positivity. The conclusions that may be drawn from these observations are twofold. Firstly, in our group of donors the number of donations that are positive for malaria is substantially lower than in Saeed and colleagues' group of donors 1 . The second important conclusion is that given our low rate of antibody positivity, it is not too inconvenient to perform the standard microscopy in a timely and thorough enough fashion to definitively exclude malaria and thus enable these TBF-and TBS-negative donations to be made available for clinical use. We have to report, however, that recently, one case of transfusion-transmitted malaria has occurred since the protocol was instituted. This case was the result of an oversight in diagnosis of a positive TBF and TBS supplementary test, which, on review after the fact, was indeed positive for ring forms of...