Visible and near-infrared absorption properties of blood from sickle cell patients and normal individuals.

Abstract

Sickle cell disease (SCD) is a genetic blood disorder characterised by red blood cells that assume an abnormal and rigid shape. A point mutation in the beta globin chain of haemoglobin results in glutamic acid to be replaced with valine at the sixth position. The abnormal haemoglobin (HbS) leads to the distortion of red blood cells in certain conditions, such as low oxygen tension, and leads to sickling. Sickling decreases the flexibility of red blood cells and causes microvascular occlusion, which may manifest as stroke, acute chest syndrome, pulmonary hypertension or organ damage. SCD occurs primarily among people of sub-Saharan African, Mediterranean, Middle Eastern and Indian descent. Of note, sickle cell anaemia refers to people who are homozygous for the mutation causing HbS, while sickle cell trait refers to heterozygotes who have one normal haemoglobin gene and one sickle cell gene. Approximately 250,000 children worldwide are born each year with sickle cell anaemia. According to the Gulf Genetic Center (GGC), abnormal haemoglobin was detected in 44.35% of neonatal samples in Bahrain. Of those, 18.1% had sickle cell trait and 2.1% had SCD. Additionally, the GGC reported that in the non-neonatal cases, the overall frequency of SCD was found to be 10.44%. Several techniques are used to screen for sickle cell trait or SCD, such as high-performance liquid chromatography (HPLC), haemoglobin electrophoresis and DNA sequencing. HPLC uses ultraviolet rays to detect the difference in shape and surface area between the normal blood cells and the sickle cells. Haemoglobin electrophoresis differentiates between the haemoglobin forms based on charge, while DNA sequencing of the haemoglobin gene can detect the presence of the single amino acid substitution implicated in SCD. First reported in 1942, five different formsof haemoglobin (oxyhaemoglobin, carbomyl haemoglobin, methaemoglobin, reduced haemoglobin and metcyanhaemoglobin) were detected based on marked differences in the absorption spectra in the visible (380nm-760nm) and near-infrared (760nm-2,500nm) region of the electromagnetic spectrum. No such investigation comparing the absorption spectra of normal adult haemoglobin (HbA) and sickle cell haemoglobin (HbS) has been conducted in the visible and near-infrared region. Such is the aim of this brief study.</p