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Diagnosis Bill Brieger | 16 Sep 2008 01:24 am

Rapid diagnostic tests – value and trust

A variety of rapid diagnostic tests (RDTs) have been developed to detect malaria parasites in primary care settings.  RDTs are in part a response to the higher costs of artemisinin-based combination therapies (ATCs) and the need to reduce wholesale use of ACTs for any fever in hopes of preserving efficacy longer. Because of the great threat of malaria to children under five years of age, most endemic countries still permit presumptive treatment with ACTs for these children.  RDTs therefore, can be an important component of case management in adult populations.

Even though the cost of arthmether-lumefantrine (AL) have been brought down, and efforts are underway to achieve similar cost reductions for artesunate-amodiaquine products, there still exists justification for RDTs from the standpoint of preserving efficacy.  Charlotte Zikusooka and colleagues have documented that, “Compared to treating patients on the basis of clinical diagnosis, the use of RDTs in all clinically diagnosed malaria cases results in cost savings only when 29% and 52% or less of all suspected malaria cases test positive for malaria and are treated with AS+SP and AL, respectively.” The cost savings is obviously also dependent on the relative price of RDTs compared to adult dose costs of ACTs.

These researchers ultimately conclude that, “While the use of RDTs in all suspected cases has been shown to be cost-saving when parasite prevalence among clinically diagnosed malaria cases is low to moderate, findings show that targeting RDTs at the group older than six years and treating children less than six years on the basis of clinical diagnosis is even more cost-saving. In semi-immune populations, young children carry the highest risk of severe malaria and many healthcare providers would find it harder to deny antimalarials to those who test negative in this age group.”

rdt-moz.JPGThe study benefits hinge on health worker judgement: “This result holds true only if health workers prescribe and or dispense antimalarials to only the patients that are found to be malaria test positive.”  Discussion with primary care clinic staff in Mozambique recently showed that this may be a major stumbling block.  Apparently they administer the RDTs, but do not trust the results, so send the client to the laboratory. Then regardless of the lab results, they tend to treat with antimalarial drugs, because ‘one never knows.’

While RDTs have an advantage among adult patients (assuming a country actually makes provision of ACTs for adults a priority), their implementation cannot be effective without proper training and follow-up supervision to reinforce correct use.

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