Figure 411

Relationship between maximal urinary osmolality and age in normal subjects and in patients with hemoglobinopathies. Results of an investigation into a large group of normal persons and those with homozygotous hemoglobin disease (Hb SS; Hb SS + Hb F), heterozygotous hemoglobin disease (Hb AS), sickle cell hemoglobin C disease (SC), hemoglobin C trait (AC), and hemoglobin C disease (Hb CC). Normal persons have a mean maximal urinary osmolality of 1058 ±SD 128 mOsm/kg H2O. The most marked impairment in concentrating capacity occurs in Hb SS disease. Maximal urinary osmolality decreases significantly in the first decade of life and stabilizes in patients over 10 years of age at a mean of 434 ±SD 21 mOsm/kg H2O. The measurement has been designated the fixed maximum of sickle cell nephropathy. In patients with Hb AS and Hb SC, a progressive decrease in maximal urinary osmolality can be observed with age. C hemoglobin alone (AC or CC) does not impair the concentrating ability of the kidneys. The renal concentrating capacity of the heterozygote (Hb AS) also is affected, but only later in life. (Adapted from van Eps et al. [13]; with permission.)

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