The introduction of ACTs has increased the urgency of improving the specificity of malaria diagnosis. The relatively high cost of these drugs makes waste through unnecessary treatment of patients without parasitaemia unsustainable. In addition to cost savings, parasitological diagnosis has the following advantages:
• improved patient care in parasite-positive patients owing to greater certainty that the patient has malaria;
• identification of parasite-negative patients in whom another diagnosis must be sought;
• prevention of unnecessary exposure to antimalarials, thereby reducing side-effects, drug interactions and selection pressure;
• improved health information;
• confirmation of treatment failures.
The two methods in use for parasitological diagnosis are light microscopy and rapid diagnostic tests (RDTs). Light microscopy has the advantage of low cost and high sensitivity and specificity when used by well-trained staff. RDTs for detection of parasite antigen are generally more expensive, but the prices of some of these products have recently decreased to an extent that makes their deployment cost-effective in some settings. Their sensitivity and specificity are variable, and their vulnerability to high temperatures and humidity is an important constraint. Despite these concerns, RDTs make it possible to expand the use of confirmatory diagnosis. Deployment of these tests, as with microscopy, must be accompanied by quality assurance. Practical experience and operational evidence from large-scale implementation are limited and, therefore, their introduction should be carefully monitored and evaluated.
The results of parasitological diagnosis should be available within a short time (less than 2 h) of the patient presenting. If this is not possible, the patient must be treated on the basis of a clinical diagnosis.
4.2.1 The choice between RDTs and microscopy
The choice between RDTs and microscopy depends on local circumstances, including the skills available, the usefulness of microscopy for other diseases found in the area, and the case-load. Where the case-load of fever patients is high, microscopy is likely to be less expensive than RDTs. Microscopy has further advantages in that it can be used for speciation and quantification of parasites, and identification of other causes of fever. However, most malaria patients are treated outside the health services, for example, in the community, in the home or by private providers; microscopy is generally not feasible in such circumstances, but RDTs may be.
The following conclusions and recommendations are based on evidence summarized by recent WHO consultations, especially the Technical Consultation on the Role of Parasitological Diagnosis in Malaria Case Management in Areas of High Transmission, held in Geneva from 25 to 26 October 2004 (report in preparation).