False-positive results for rapid diagnostic tests for malaria in patients with rheumatoid factor.

Four different rapid diagnostic tests (RDTs) for malaria were evaluated by testing 82 healthy control patients, 89 Plasmodium vivax-infected patients, and 92 rheumatoid factor (RF)-positive nonmalaria patients. The false-positive rate ranged from 2.2% to 13% in RF-positive patients. High RF levels are associated with malaria RDT false positivity.