Diagnosis
Malaria is typically diagnosed by the microscopic examination of blood using blood films or using antigen-based rapid diagnostic tests (RDT). Microscopy is the most commonly used method to detect the malaria parasite—about 165 million blood smears were performed in 2010. Despite its widespread usage, diagnosis by microscopy suffers from two main drawbacks: many settings (especially rural) are not equipped to perform the test, and the accuracy of the results depends on both the skill of the person reading the smear and the levels of the parasite in the blood. The sensitivity of blood films ranges from 75–90% in optimum conditions, to as low as 50%. Commercially available RDTs are often more accurate than blood smears at predicting the presence of malaria parasites, but they are widely variable in diagnostic sensitivity and specificity depending on manufacturer, and are unable to tell how many parasites are present.
In regions where laboratory tests are readily available, malaria should be suspected, and tested for, in any unwell patient who has been in an area where malaria is endemic. In areas that cannot afford laboratory diagnostic tests, it has become routine to use only a history of subjective fever as the indication to treat for malaria—a presumptive approach exemplified by the common teaching "fever equals malaria unless proven otherwise". The drawback of this practice, however, is overdiagnosis of malaria and mismanagement of non-malarial fever, which wastes limited resources, erodes confidence in the health care system, and contributes to drug resistance. Although polymerase chain reaction-based tests have been developed, these are not widely implemented in malaria-endemic regions as of 2012, due to their complexity.
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