Rapid diagnostic tests, or RDTs, are becoming an increasingly important method for detecting malaria. Health specialists recommend that they be used along with a range of other strategies for controlling the disease , including the use of artemisinin-based combination therapies, insecticide-treated bed nets, indoor spraying against malaria-carrying mosquitoes and testing and treatment of pregnant women and children.
The tests are ideal for rural areas are accurate, easy to use and at less than one dollar per test, inexpensive. Prior to RDTs, blood samples had to be sent to labs to be examined under a microscope. Not now. With the prick of a finger, the RDTs can detect in less than 10 minutes the most common and deadly malaria parasite in the tropics, Plasmodum falciparum.
Dr. Trenten Ruebush is a senior malaria advisor at USAID in Washington.
The major reason everyone is interested in RDTs, he adds, "is that [the cost] of the new combination malaria drugs introduced throughout Africa and other countries are 10 to 20 times higher than the former single drug therapies like chloroquine and amodiaquine. It's critical to have accurate diagnosis to ensure those expensive drugs are being used in those who are infected and do need them. You don't want to use those expensive drugs in someone who has a fever due to another cause.
But health specialists say some field technicians continue to prescribe expensive anti-malarials despite a negative reading by the RDTs.
Ruebush says, "whether a clinician or health worker in a rural health clinic will pay attention to the results of a microscopic examination of the blood or of an RDT is another matter. It does happen more often than it should that when the results of the diagnostic tests don't agree with what the health worker believes to be the case, the health worker will often give the treatment anyway. And then, yes, it does defeat the purpose of the tests, but as RPTs are being scaled up in Africa, efforts are being made to educate health workers about the appropriate use of the test and the patient to know that a negative test from an RDT means you do not have malaria. It does not mean you are not ill. It just means you do not have malaria."
Rima Shretta is a senior program associate for Management Sciences for Health in Arlington, Virginia. She says her group is interested in collecting data on the way African health workers use the tests. However, she notes that the World Health Organization recommends that one group does not need to be treated with RDTs, but can be treated with just a clinical diagnosis: children under five living in high malaria transmission areas with symptoms such as fever. She says they are among the most vulnerable to the disease and that it's very likely that malaria is the cause of their current fever. For that reason, she says it's not cost effective to spend the money on rapid diagnostic tests.
The mortality rate for children under five is high," she says, "and [there is the] likelihood [that these children's] have malaria if their fever is quite high. [There is a probability that they will have malaria which may progress very rapidly to severe disease in the absence of treatment due to low levels of immunity]. In areas with no RDTs what they recommend is that clinical diagnosis [based on observed symptoms] -- which had been the cornerstone for children under five -- continue to be used as opposed to RDTs because there is a high likelihood they will have malaria anyway. Guidelines on the integrated management of childhood illnesses (imci) recommend that fever be used as a proxy for malaria.
Shretta says her organization is also assessing the supply chain to ensure the quality of the test kits, which must be stored in temperatures lower than 30 degrees Celsius to maintain their accuracy and reliability. Meanwhile, the WHO is compiling data that help donors and other buyers assess the quality of the 40 or so tests now on the market.