 False positive dipstick results were reported in patients with rheumatoid-factor-positive rheumatoid arthritis.Since HRP-2 is expressed only by "P. falciparum", these tests will give negative results with samples containing only "P. vivax", "P. ovale", or "P. malariae"; many cases of non-falciparum malaria may therefore be misdiagnosed as malaria negative (some "P.falciparum" strains also don't have HRP II).The variability in the results of pHRP2-based RDTs is related to the variability in the target antigen.