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When malaria rapid tests fail

Malaria testing - Following a finger prick, a capillary tube is filled with blood. The sample is then spun and the proportion of the blood made up of red blood cells is measured = packed cell volume (PCV). Date: 1991 WHO/TDR/S.Lindsay
S'il n'y a pas de malaria, alors ? (photo d'archives)
World Health Organization (WHO) and the non-profit Foundation for Innovative New Diagnostics (FIND) have released the largest, independent laboratory evaluation of malaria rapid diagnostic tests (RDTs) for World Malaria Day, which shows that while some tests accurately detect even slight traces of malaria in tropical temperatures, others give false results, missing potentially life-saving diagnoses.


FIND scientist David Bell told IRIN that a country's temperature, its rate of malaria outbreaks and the type of mosquito spreading the disease determine the appropriate RDT, but that generally, “you want a more sensitive test” able to detect malaria antibodies even at low concentrations.

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According to the report, rapid tests CareStart Malaria HRP2 and First Response Malaria Ag HRP2 manufactured by Access Bio and Premier Medical Corporation, respectively, detected in 100 percent of the tests malaria infections by one type of mosquito. Both RDTs detected with 95-percent accuracy infections from two major disease-spreading species – even at low concentrations.

The problem until now is that the malaria RDT market has been unregulated, said FIND’s Bell, “These manufacturers know their tests must meet a bar [of performance in detection], but it is hard and expensive to get [malaria-infected blood] samples to evaluate the tests.”

“Collecting blood samples is not easy. We must wait for malaria season. And it is unpredictable how many samples can be taken.” Malaria-infested areas are often cut off during the rainy season – when much of malaria hits – due to poor or non-existent roads.

The result has been spotty performance among some of the 60 brands available – and even within tests from the same manufacturer, Bell told IRIN.

Because of this, manufacturers may release RDTs for sale without adequate testing, which can lead to inaccurate diagnoses, according to FIND. “With a good manufacturer, these tests do not make it to market,” said Bell.

“Lot” testing

But Bell told IRIN low-quality tests do slip into the market in remote communities far from laboratories, which increasingly rely on RDTs to detect malaria antibodies with a simple finger prick.

The scientist estimated up to 70 million rapid tests are used every year, mostly in Africa.

RDTs can be damaged in transit, or were never good in the first place, which makes laboratory evaluation of the tests before use critical, said Bell. FIND conducts “lot testing”, or mass testing, at no cost if countries send their RDTs to regional laboratories in Cambodia, Philippines, or Ethiopia. Results and RDTs are sent back generally within two weeks.

''The hope is that once a disease is determined to not be malaria, there will be a higher pick-up rate of other fever diseases''
FIND currently evaluates about 15 percent of RDTs in use, of which five percent do not meet standards, said Bell – or more than five million tests based on his high estimate of RDTs in circulation.

But Bell said even more tests may be flawed. “We test for donors who have stringent procurement guidelines and do their own quality control. The failure rate may go up if it is a random market sample.”

WHO and FIND are evaluating an additional 29 malaria rapid tests. Results are due in 2010.

About one million people are reported to die from malaria infections every year, mostly in sub-Saharan Africa, according to WHO.

But in some countries that have widely adopted malaria rapid testing, the number of suspected malaria cases has dropped dramatically. In 2008 Senegal had a 74-percent drop in cases reported as malaria after it adopted rapid testing in October 2007, according to its National Malaria Control Programme.

Bell told IRIN accurate malaria rapid tests can improve treatment of other high-fever diseases, including meningitis and typhoid. “They [malaria RDTs] can have a huge impact on overall public health. The hope is that once a disease is determined not to be malaria, there will be a higher pick-up rate of other fever diseases, which can bring down morbidity with quick diagnoses.

“This is not just about malaria.”

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