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Comparative Erythrocytes Osmotic Fragility Test and some Haematological Parameters in HbAA and HbSS subjects
Erythrocytes osmotic fragility and haematological parameters of subjects with HbAS (sickle cell trait) and HbSS (sickle cell anaemia) were determined and compared with subjects with HbAA (normal adult haemoglobin), which acted as control. They were divided into three groups of 40 subjects for HbAA, 35 subjects for HbAS and 30 for HbSS. HbAA erythrocytes showed a higher degree of susceptibility to lysis than both HbAS and HbSS erythrocytes in buffered hypotonic sodium chloride solution. There were variations in the profiles of osmotic fragility curves for HbAA, although there was no significant difference in their MCF values. It was observed that HbAA erythrocytes completely haemolysed under 12.24 ± 0.25 minutes (n = 40) at 0.60g/dl sodium chloride solution. This value was significantly lower than that of HbAS which was 21.02 ± 0.32 minutes and HbAS in turn which was significantly lower than HbSS as well (p < 0.0001). Erythrocytes with HbSS type showed corpuscular haemaglobin concentration that was significantly lower than HbAA and HbAS (p < 0.0001); mean values of HbAA and HbAS did not show any significant difference. In contrast, HbAA erythrocytes showed mean corpuscular volume (MCV) value that was significantly lower than those of HbAS and HbSS (p < 0.001). Although the MCV value for HbAS erythrocytes was lower than HbSS, it was not statistically significant. The study showed that the presence of the sickle haemaglobin (HbS) whose structure conferred on the cell a larger volume as indicated by the highest mean MCV value coupled with its reduced corpuscular haemoglobin content may account for the left-ward shift of HbAS and HbSS curves. Again, erythrocytes with HbS will normally take a longer time to reach and exceed their critical haemolytic volume than those with HbA type, with a resultant effect that HbSS erythrocytes of healthy subjects are more resistant to lysis than HbAS and HbAA in buffered hypotonic sodium chloride solution.
Keywords: Erythrocytes, osmotic fragility, haematological parameters
Journal of Medical Laboratory Sciences Vol. 14 (1) 2005: pp. 1-5