Simultaneous use of Plasmodium falciparum crude antigen and red blood cell control antigen in the enzyme-linked immunosorbent assay for malaria.

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 greater than or equal to 2.92, P less than or equal to 0.05) and for calculation of the mean difference in absorbance values (delta ABS) 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, delta ABS values in ELISA were highly correlated to titers obtained in immunofluorescence (r = 0.80, P less than 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.