Malaria Diagnosis

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By Dr Ananya Mandal, MD

Diagnosis of malaria is made with the help of microscopic examination of the blood samples. The symptoms of malaria may resemble flu, gastroenteritis, typhoid or other viral fevers. Thus fever and other symptoms similar to malaria need careful evaluation to diagnose malaria.

Differential diagnosis

Conditions that mimic malaria and need to be ruled out before diagnosis of malaria include:-

Viral Hepatitis A, B or C
Typhoid fever
Dengue fever
Influenza
Viral fevers
HIV infection
Meningitis or encephalitis brain infections

Steps in diagnosis of malaria

History of travel to a high risk zone or a history of bite. Detailed history of travel to endemic areas even brief stopovers should be recorded.
Early diagnosis is important to ensure appropriate, presumptive and accurate treatment and to reduce the risk of life threatening complications and death. A blood sample is usually taken for diagnosis.
Thick and thin blood smears are taken on a glass slide. The samples best show a confirmatory diagnosis during a bout of fever when the parasite is present in the peripheral blood stream. The smears on the glass slides are then stained with Giemsa stain. The slides are viewed under the microscope and the parasite is identified. This is the gold standard method of diagnosis and remains one of the cheapest and most cost effective methods. Other advantages include high sensitivity and specificity when used by well-trained staff. Where the blood film is negative, at least 2 further films should be obtained over the next 48 hours before malaria is ruled out. A negative report does not necessarily mean the individual has no malaria. This is particularly the case in pregnancy when the parasites remain clustered in the placenta and may not be easily detected.

Rapid diagnostic tests (RDTs) are also employed for easy detection and take around 2 to 15 minutes. These tests detect parasite antigens. These can be used by relatively untrained staff.

Polymerase chain reaction (PCR) is a more sophisticated method of diagnosing malaria. It is expensive and less available at endemic zones. Parasite nucleic acids are detected using PCR. PCR is most useful for confirming the species of malarial parasite after the diagnosis has been established by either smear microscopy or RDT.
Serology may also be used to detect antibodies against malaria parasites. This can be done using either indirect immunofluorescence (IFA) or enzyme-linked immunosorbent assay (ELISA). Serology does not detect current infection but rather measures past exposure.

Apart from detection of the parasite other tests are also ordered. These include complete blood counts that reveal anemia, low platelet counts and rarely high white blood cell counts.
G6PD activity is seen to prevent side effects of some anti-malarial drugs like primaquine.
Liver and kidney functions are evaluated to rule out organ damage.
Urea and electrolytes are assessed to check for acidosis and low sodium and high creatinine levels.
Blood glucose is assessed as hypoglycaemia is common with falciparum malaria.
Other tests include assessment of blood gases, blood culture, blood clotting studies, chest X ray, urine and stool cultures and examination of the Cerebrospinal fluid (CSF) by lumbar puncture.