Malaria

Malaria remains endemic in many countries and can be fatal if left undiagnosed. There should not be a delay in testing if the clinical history and epidemiology suggests a possible diagnosis of malaria.

Diagnosis of Malaria by Microscopy (essential for a suspected medical emergency)

All suspected acute malarial infections MUST be urgently diagnosed by slide microscopy.

• Sample type: A minimum of 2ml of EDTA anti- coagulated blood sent without delay.

Diagnosis will be made by thick and thin film microscopy, ideally using fresh blood. Delay in receipt of an EDTA specimen can adversely affect the integrity of the sample and consequently make accurate diagnosis difficult.

For users other than University College London Hospitals NHS Trust, please make 2 thin and 2 thick films for examination and send together with any original slides from the blood sample in addition to the original blood sample.

Samples are also screened with a Rapid Diagnostic Malaria Antigen Test (RDT). This utilises lactate dehydrogenase (LDH) for pan-malarial species detection and Histidine- rich protein (HRP-2) for Plasmodium falciparum specific identification.

Please note, due to rare gene deletionsin Plasmodium falciparum species, this test can result in false negatives and we recommend its use in conjunction with microscopy.

Malaria serology is NOT suitable for diagnosing acute infection.

Diagnosis of Malaria by PCR

This is useful for suspected slide negative, sub patent, on going malaria infections and species identification where morphology is inconclusive.

• Sample type: A minimum of 0.5ml of EDTA anti-coagulated blood.

For suspected malaria infections that are repeatedly negative by slide microscopy, highly sensitive diagnosis may be made by the use of species specific PCR. Alternatively, where the morphology is inconclusive, species identification may be performed on old microscopy positive bloods to identify P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi.

Diagnosis of Malaria by Serology

This is useful for suspected past infection and blood, tissue and organ donor screening.

• Sample type: A minimum of 0.5ml of serum or EDTA plasma is required.

Serology for malaria may be requested for the following reasons:

• If for some reason it is important to attempt a retrospective diagnosis.
• For the investigation of splenomegaly or nephrotic syndrome in a patient who might have been exposed to malaria.
• For donor screening where the donor has potentially been exposed to malarial infection.

It is NOT recommended for the investigation of acute fever, as urgent blood film examination is the method of choice. An ELISA assay is performed using Plasmodium falciparum and vivax antigens. Positive results will be reported as an optical density and a cut-off point will be stated.

Sera/plasma from suspected Tropical Splenomegaly Syndrome patients will be tested by IFAT if the ELISA is positive.

The malaria ELISA used cannot be used to identify the species in malaria infections.