Traditionally to rule out a diagnosis of malaria requires three negative blood films. But in the era of routine rapid diagnostic testing, some are questioning the need for continued serial testing. A new study, published online Dec. 3 in theAmerican Journal of Tropical Medicine and Hygiene, shows that for patients not taking anti-malarial therapy nearly all malaria diagnosis are made with the initial blood film and rapid diagnostic test, possibly obviating the need to continue serial testing. Australian researchers examined 255 cases of malaria diagnosed from 1999 to 2010 at three laboratories in a nonendemic area. Standard operating procedures at the three labs require that all clinical requests for thick and thin blood films for malaria also have a reflex rapid diagnostic testing performed (BinaxNOW immunochromatographic test). Plasmodium falciparum malaria was diagnosed on the first diagnostic set in all but one case (99 percent), while initial tests detected more than 97 percent of cases for non–P. falciparum malaria. Nine cases of malaria (3.5 percent) had negative results for the initial blood film and rapid diagnostic test but were diagnosed on the second film. The researchers say that each of the missed cases was atypical with four of the patients having […]
Traditionally to rule out a diagnosis of malaria requires three negative blood films. But in the era of routine rapid diagnostic testing, some are questioning the need for continued serial testing. A new study, published online Dec. 3 in theAmerican Journal of Tropical Medicine and Hygiene, shows that for patients not taking anti-malarial therapy nearly all malaria diagnosis are made with the initial blood film and rapid diagnostic test, possibly obviating the need to continue serial testing.
Australian researchers examined 255 cases of malaria diagnosed from 1999 to 2010 at three laboratories in a nonendemic area. Standard operating procedures at the three labs require that all clinical requests for thick and thin blood films for malaria also have a reflex rapid diagnostic testing performed (BinaxNOW immunochromatographic test). Plasmodium falciparum malaria was diagnosed on the first diagnostic set in all but one case (99 percent), while initial tests detected more than 97 percent of cases for non–P. falciparum malaria. Nine cases of malaria (3.5 percent) had negative results for the initial blood film and rapid diagnostic test but were diagnosed on the second film. The researchers say that each of the missed cases was atypical with four of the patients having received anti-malarial medication, which is known to lower parasite density and modify the appearance of parasites on blood films.
Despite research showing that rapid diagnostic tests have excellent test characteristics to exclude malaria, serial testing is still recommended. Serial testing requires laborious sample preparation and examination of blood films that hampers laboratory workflow, hospital efficiency, and increases patient wait times and costs. With the vast majority of malaria diagnoses made on the first set of tests, continuing serial testing may be unnecessary.
“Our findings suggest that for patients with imported malaria who have not been exposed to anti-malarial drugs, the diagnosis is likely to be made on the first set of thick and thin blood films combined with rapid diagnostic tests,” write the authors, led by Janet Pasricha, from Royal Melbourne Hospital. “Larger, prospective studies are now required to assess the safety of this approach.”
