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Laboratory tests

Thick and thin blood films

Ideally, three blood tests of both thick and thin blood films should be collected 12-24 hours apart to diagnose malaria. These tests are currently the ‘gold standard’ for malaria detection and identification.

Thick films are sensitive tests for diagnosing malaria infection. A large number of red blood cells are looked at under the microscope to find parasites within the cells. The number of infected red blood cells can also be calculated so that the parasite load is known.

Thin films are done with fewer blood cells examined per slide, but these tests allow identification of the type of Plasmodium species causing the infection. This is essential for correct treatment.

Rapid diagnostic tests
These tests detect a malaria antigen (protein) in the patient’s blood, and signify a positive result by a colour change on the testing strip. They are sometimes called ‘dipstick’ tests.

Different rapid diagnostic tests are available, and they may detect only Plasmodium falciparum, or may detect other species.

These tests are most commonly used in remote areas where there is not access to accurate microscopy (so that blood films cannot be used). In Australia and other countries where malaria is not commonly seen, these tests are used in laboratories where there is insufficient experience to allow accurate microscopy. This allows rapid and accurate diagnosis and early treatment of malaria, which is essential to improve patient outcomes. In Australia further tests are usually then done to confirm the diagnosis, often in a central laboratory.

Polymerase chain reaction (PCR)
The polymerase chain reaction amplifies malaria DNA and allows detection and identification of the Plasmodium species. This test can be used to confirm the diagnosis in laboratories where there is a lack of microscopy experience. It is also useful in cases of low parasite loads or mixed infections, where microscopy may be less accurate. The cost of these techniques limits their use in many regions where malaria is endemic.

Last Review Date: November 6, 2017