Comparison of three antigen detection methods for diagnosis and therapeutic monitoring of malaria: a field study from southern Vietnam

OBJECTIVES To compare the sensitivity, specificity and post-treatment persistence of three commonly used rapid antigen detection methods. METHOD We studied 252 Vietnamese patients aged from 4 to 60 years, 157 with falciparum and 95 with vivax malaria and 160 healthy volunteers. An initial blood sample was taken for microscopy, and OptiMAL®, immunochromatographic test (ICT) malaria P.f./P.v.® and Paracheck-Pf® tests. Patients with falciparum malaria were treated with an artesunate-based combination regimen and those with vivax malaria received chloroquine. Eighty-seven patients with falciparum malaria who were initially positive for one of the antigen tests and who remained blood smear-negative underwent follow-up testing over 28 days. RESULTS Paracheck-Pf® was the most sensitive test for Plasmodium falciparum (95.8% vs. 82.6% for ICT malaria P.f./P.v.® and 49.7% for OptiMAL®). Specificities were all 100%. For vivax malaria, OptiMAL® performed better than ICT malaria P.f./P.v.® (sensitivities 73.7% and 20.0%, respectively), with 100% specificity in both cases. All tests had low sensitivities (≤ 75.0%) at parasitaemias  10 000/μl). Residual OptiMAL® positivity occurred only in a relatively small proportion of patients (  10 000/μl during the first 2 weeks after treatment. CONCLUSIONS Although microscopy remains the gold standard for malaria diagnosis, Paracheck-Pf® may prove a useful adjunctive test in uncomplicated falciparum malaria in southern Vietnam. OptiMAL® had the lowest sensitivity for P. falciparum but it might have a use in the diagnosis of vivax malaria and perhaps to monitor efficacy of treatment for falciparum malaria where microscopy is unavailable.