Simultaneous Use of Plasmodium falciparum Crude Antigen and Red Blood Cell Control Antigen in the Enzyme-Linked Immunosorbent Assay for Malaria

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Abstract
An enzyme-linked immunosorbent assay for malaria, based upon duplicate testing of serum samples on both a crude Plasmodium falciparum antigen and a red blood cell control antigen, is evaluated. Results were analyzed using the Student's t-test for identification of positive serum samples (t ≥ 2.92, P ≤ 0.05) and for calculation of the mean difference in absorbance values (ΔABS) obtained between the P. falciparum wells and the control wells. Cross-evaluation with the IFA test for P. falciparum antibodies gave 89.6% concording positive or negative results. Among discrepant sera 8.35% were ELISA+/IFA- and 2.05% ELISA-/IFA+. In addition, ΔABS values in ELISA were highly correlated to titers obtained in immunofluorescence (r = 0.80, P < 0.001). The results confirm the high degree of species-specificity of the ELISA using P. falciparum crude antigen. The necessity of the simultaneous use of red blood cell control antigen with a crude plasmodial antigen is demonstrated by comparing the presented results with those obtained on the P. falciparum antigen only.