New enzymatic assay, parasite lactate dehydrogenase in diagnosis of malaria in Kenya

Background: The unique ability of plasmodial lactate dehydrogenase p(LDH) to utilise 3-acetyl pyridine dinucleotide (APAD) in lieu of NAD as a coenzyme in the conversion of pyruvate to lactate, led to the development of a biochemical assay for the detection of plasmodial parasitaemia. Researchers have reported that p(LDH) activity of plasmodia could be used as an assessment of parasitaemia since human red blood cells do not utilise APAD in the metabolism of glucose. Objective: To use p(LDH) for field and clinical diagnosis of malaria in endemic regions of Kenya. Design: Prospective field and clinical study. Setting: Kisumu District Hospital and Walter Reed malaria laboratory in Kenya. Subjects: The study subjects were of three different categories: the healthy non-infected individuals staying out of malaria endemic region (controls group 1), the nonparasitaemic and parasitaemic non- symptomatic healthy individuals living in endemic region {both field study group 2}, the non-parasitaemic and parasitaemic symptomatic individuals living in endemic region {both clinical study group 3}. Results: In the clinical studies, thin smear microscopy gave the highest sensitivity as 75.6% for plasma, while the highest specificity was 71.4%. For red blood cells, the highest sensitivity was 78.4% while specificity was 80%. In the field trials, the highest sensitivity was 89% using thin smear microscopy whereas the specificity was 45% for plasma cut off using thick smear. For red blood cells, the highest sensitivity was 79% while specificity was 66.7%. Conclusion: The variations in sensitivity and specificity of this assay in comparison to microscopy is a strong indication that p(LDH) may be measuring even the sequestered parasites that cannot be visualised by microscopy. The results of this study validates the use of p(LDH) as an alternative objective test for malaria diagnosis against microscopy. East African Medical Journal Vol.82(3) 2005: 112-11