Comparison of immunofluorescence antibody testing and two enzyme immunoassays in the serologic diagnosis of malaria.

Background: Serologic testing in malaria has traditionally been done by immunofluorescence antibody testing (IFA), but the use of commercially available enzyme immunoassays (EIAs) has become more widespread.

Methods: We compared IFA with two commercial EIA kits, the Cellabs Pan Malaria CELISA and the Newmarket Malaria EIA. Seventy-five samples from 74 patients with clinically suspected malaria were examined by both EIA kits. The samples were also examined by IFA (n= 48) and/or Giemsa-stained blood smear (n= 48).

Results: Using a consensus result as a gold standard, the agreement, sensitivity, and specificity were, respectively, as follows: Cellabs EIA 93.2, 95.5, and 92.2%; Newmarket EIA 87.7, 68.2, and 96.1%; and IFA 89.1, 86.4, and 91.7%. Compared to positive Giemsa-stained smears, the sensitivities were as follows: Cellabs EIA 90.9% (10/11), Newmarket EIA 54.5% (6/11), and IFA 100% (11/11). Antinuclear antibody (ANA)-positive sera (n= 11) and rheumatoid factor (RF)-positive sera (n= 11) showed no cross-reactivity with the Newmarket EIA, while the Cellabs EIA yielded positive results in one ANA-positive and two RF-positive sera. Among healthy blood donors (n= 50), the Newmarket EIA showed 100% specificity (50/50) and the Cellabs EIA showed a specificity of 92% (46/50).

Conclusions: While the Newmarket EIA was a generally more specific assay, it was insufficiently sensitive relative to the IFA and the Cellabs EIA for screening purposes for malaria antibodies. The Cellabs EIA demonstrated the best overall sensitivity and is a reasonable choice as a serodiagnostic tool for malaria. It may also be useful as an adjunct to Giemsa-stained smear examination, to aid in cases of low parasitemia in previously nonimmune individuals.