Approach to Malaria Diagnosis

A clinician who faces a case of fever would need answers to the following questions:

  • Is it malaria?
  • If yes;
    • What is the species?
    • Is it severe?
    • Is it new/ recurrence?
    • Is it active?

At present, ONLY the peripheral smear can provide answers to ALL these questions on a single test. With trained technicians, blood smear remains the gold standard for detection, for speciation, for parasite count and for identification of different forms of the parasites. Therefore, rely ONLY on peripheral smear for speciation, parasite count and identification of parasite forms. The QBC test performed by trained personnel could match a thick blood smear for detection of malaria. The RDTs cannot be used as reliable tools for diagnosis of malaria.

Approach to Malaria Diagnosis

approach-diagnosisEvery case of fever, in an area of malaria transmission and among travelers returning from such areas, must be tested for malaria. In many remote and poor parts of India and elsewhere where malaria is endemic, facilities for malaria microscopy are either non existent or inaccessible. Microscopes, stains, power sources or technicians are unavailable either in toto or in parts. Diagnosing malaria in such areas is indeed a challenge.

The National Vector Borne Disease Programme in India recommends peripheral smear microscopy for all fever cases wherever facilities are available. In remote areas where microscopy is unavailable for 24 hours or more, bivalent RDT can be used to diagnose malaria. In some parts of India, QBC is being used instead of blood smear microscopy; however, this method is not approved by the NVBDCP. If a patient is positive with either microscopy or RDT, he/she must be started on relevant anti malaria drugs, based on the species. As RDT is neither very sensitive nor very specific for malaria, it is desirable to confirm every positive test with a blood smear at the earliest opportunity, the smear having been collected before initiating the treatment. All negative tests on microscopy may also need repeat tests at 12-24 hour intervals, on 2-3 occasions, to rule out malaria. Negative tests on RDT may also be candidates for repeat examination on blood smear, particularly when the patient is having features of severe illness wherein RDT may show a false negative test due to prozone effect. RDT may show false positive tests due to persistent antigenemia for 2 months after a primary malaria infection and this fact must be borne in mind while interpreting the test result in patients who return with fever within that period.

 © ©BS Kakkilaya | Last Updated: Mar 10, 2015

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