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Dr Elochukwu Adibo
More often than not, many Nigerians immediately suspect malaria when they feel unwell with feverish symptoms, given the endemic nature of the disease in the country. Such individuals are often taken aback when laboratory test results for malaria return negative.
A negative malaria parasite test result simply means that the test procedure did not detect the presence of the parasite. However, in some cases, this does not necessarily mean that the patient is free from malaria. This highlights the need for a clear understanding of what malaria testing entails and the factors that could lead to undetected malaria in the laboratory.
In an exclusive interview, the Managing Director/CEO of EL-Lab Medical Diagnostics and Research Centre, Dr Elochukwu Adibo, explained that there are different methods of malaria screening and identification. He noted that EL-Lab and many other medical laboratories utilise the gold standard for malaria diagnosis—microscopy with visualisation of Giemsa-stained parasites in a blood sample (thick and thin films). This method also enables species identification and parasite density estimation.
“Species determination is made based on morphological characteristics of the five species of human malaria parasites and the infected red blood cells,” he stated.
Diagnosis and testing
Regarding diagnosis and testing, Adibo noted that the effectiveness of the microscopy technique depends on the quality of reagents, the microscope, and the experience of the laboratory scientist.
“We, therefore, cannot overemphasise the importance for medical laboratory scientists to maintain maximum competency in peripheral blood smear evaluation for malaria and other blood-borne parasites,” he asserted.
To ensure this, EL-Lab enrols its medical laboratory scientists annually in the malaria microscopy training programme organised by WHO-trained malaria microscopy specialists at the Nigerian Institute of Medical Research (NIMR).
On Rapid Diagnostic Testing (RDT), Adibo emphasised that EL-Lab, a leading indigenous medical diagnostic centre with an ISO15189:2022 accredited laboratory, utilises a quality-assured RDT for malaria diagnosis.
“RDT kits approved by the National Malaria Elimination Programme are employed for malaria diagnosis in EL-Lab,” he said.
Meanwhile, he acknowledged that polymerase chain reaction (PCR) assays are the most sensitive and specific method for detecting malaria parasites but are primarily used in research settings.
Understanding false or negative results
Dr Adibo stressed the importance of distinguishing between true negative and false negative results.
“A true negative test result means that the patient or client does not have malaria, while a false negative malaria test result means that the patient has malaria, but the test failed to detect the parasite,” he explained.
He outlined several factors that could contribute to false negative results.
“False negative results may be due to low parasite density (<50 parasites/uL), RDT failure, poor performance of specific RDT brands and lots, procedure error, poor storage conditions of kits or reagents, PFhrp2/3 gene deletion, quality of (Giemsa) stain, pre-erythrocytic stage of malaria infection, and patients already on treatment prior to testing,” he noted.
How to minimise false negative results
To reduce the occurrence of false negative results, Adibo highlighted three key measures: timing of blood collection, repeat testing, and laboratory competence.
“For blood collection, it should be done immediately upon suspicion of malaria, although the optimum time is about midway between chills to ensure obtaining stages in which species identification can be made. The diagnosis of malaria can be missed when there is a significant time lag from exposure and negative initial test,” he explained.
Since a negative blood smear does not entirely rule out malaria, he recommended conducting repeat tests.
“A negative blood smear makes the diagnosis of malaria unlikely, but because individuals’ symptoms may persist, successive blood smears should be repeated every 12 to 24 hours over a period of two days. The number of malaria parasites may vary at different times each day, and a single blood smear may not reveal organisms,” he advised.
On laboratory competence, Adibo spoke on the quality assurance measures at EL-Lab.
“We partake in external quality assurance (EQA) programmes, and personnel are regularly subjected to periodic peer-to-peer reviews. In EQA, we carry out RDT testing on samples from other reference laboratories; we also evaluate stained blood films for malaria parasites. Over the years, we have demonstrated remarkable competence in EQA assessment,” he said.
He added that internal quality control is equally prioritised.
“Internally, our peer-to-peer review on malaria microscopy has sharpened the diagnostic skill of our team members in malaria species identification and quantification. This peer review is followed by laboratory knowledge-sharing sessions on malaria screening. Our newly recruited medical laboratory scientists are also trained to attain malaria diagnostic competency to ensure uniform quality across board,” he stated.
Dr Adibo stressed the importance of clinical judgment in malaria diagnosis.
“Clinicians must always consider the diagnosis within the appropriate clinical setting, as a missed diagnosis can potentially result in serious consequences,” he warned.
