A defect in urine concentrating ability occurs in individuals with sickle cell trait (HbAS). This may result from intracellular polymerization of sickle hemoglobin (HbS) in erythrocytes, leading to microvascular occlusion, in the vasa recta of the renal medulla. To test the hypothesis that the severity ofthe concentrating defect is related to the percentage of sickle hemoglobin present in erythrocytes, urinary concentrating ability was examined after overnight water deprivation, and intranasal desmopressin acetate (dDAVP) in 27 individuals with HbAS. The HbAS individuals were separated into those who had a normal a-globin genotype (aa/aa), and those who were either heterozygous (-a/aa) or homozygous (-a/-a) for gene-deletion a-thalassemia, because a-thalassemia modulates the HbS concentration in HbAS. The urinary concentrating ability was less in the aa/aa genotype than in the -a/aa or -a/-a genotypes (P < 0.05). After dDAVP, the urine osmolality was greater in patients with the -a/-a genotype than with the -a/aa genotype (882±37 vs. 672±38 mOsm/kg H20) (P < 0.05); patients with the -a/aa genotype had greater concentrating ability than individuals with a normal a-globin gene arrangement. There was an inverse linear correlation between urinary osmolality after dDAVP and the percentage HbS in all patients studied (r = -0.654; P < 0.05). A linear correlation also existed for urine concentrating ability and the calculated polymerization tendencies for an oxygen saturation of 0.4 and 0 (r = -0.62 and 0.69, respectively). We conclude that the severity of hyposthenuria in HbAS is heterogeneous. It is determined by the amount of HbS polymer, that in turn is dependent upon the percentage HbS, which is itself related to the a-globin genotype. (J. Clin.
The variable concentration of HbS in individuals with sickle cell trait led us to study the relationship between HbS level and selected vascular events in 355 hospitalized black men with sickle cell trait. There were significant differences in hemoglobin concentration and mean corpuscular volume found in four groups divided by their HbS level, the lowest proportion of HbS (less than 30%) being associated with the lowest hemoglobin concentration (12.6 g/dl) and MCV (77 fl). The percent HbS did not influence the incidence of pulmonary embolism, thrombophlebitis, myocardial infarction, cerebrovascular accident, or idiopathic hematuria. Our results suggest that HbS level does not influence vascular disease, and while certain hematological alterations occur, they are very unlikely to have any clinical significance. Regardless of the proportion of HbS, sickle cell trait in black men is benign.
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