Pb2558: reference values for methemoglobin level and nadh-cytochrome b5 reductase activity in tunisian population.

Topic: 28. Enzymopathies, membranopathies and other anemias Background: Methemoglobin (MetHb) is a form of hemoglobin produced when the ferrous iron (Fe+2) is oxidized into ferric iron (Fe+3). MetHb is unable to bind oxygen, and its over production leads to methemoglobinemia characterized by impaired aerobic cellular metabolism, hypoxia, chocolate-brown colored blood and mucous membranes, cyanosis, and in rare cases to death. In normal physiological settings, MetHb remains below 1% through the NADH-cytochrome b5 reductase system, which converts the Fe+3 back to Fe+2. Deficiency in NADH-cytochrome b5 reductase enzyme, leads to MetHb accumulation, and therefore to recessive congenital methemoglobinemia (RCM). Reference values of normal range of methemoglobin and NADH-cytochrome B5 reductase are therefore crucial in the methemoglobinemia diagnosis. These reference intervals have been determined in several populations, but not in Tunisian population. Aims: The aim of this study was to establish the reference values of MetHb and NADH-cytochrome B5 reductase in Tunisian population. Methods: Our reference population consisted of 52 healthy hematology-based nonsmoking individuals. We carried out spectrophotometric measurements of MetHb level and NADH-cytochrome b5 reductase activity at 633 nm and 320 nm, respectively, according to the Dacie and Lewis method and Beutler. The results obtained were statistically analyzed by SPSS software to estimate the mean, standard deviation, and reference interval. This study was approved by the Pasteur Institute’s Biomedical Ethics Committee, Tunisia. Results: The sex ratio of the reference population was 0.52 and the mean age was 49 ± 15.55 Based on our results, the reference values are 1.89% ± 0.68 for methemoglobin and 24.42 ± 4.43 IU/g Hb for NADH cytochrome b5 reductase. Summary/Conclusion: Medical decision in diagnosis depends on the interpretation of laboratory test results compared with a reference interval. The International Federation of Clinical Chemistry (IFCC) recommends that every laboratory has to determine its own set of reference values using their own techniques and equipments. This work is the first step in the characterization of RCM in Tunisia. Keywords: Hemoglobin, Hemoglobinopathy