Urine concentrating ability in infants with sickle cell disease: baseline data from the phase III trial of hydroxyurea (BABY HUG).

BACKGROUND: A urine concentrating defect is quite common in sickle cell anemia, has its onset in early childhood, and may be reversible with transfusion. The Pediatric Hydroxyurea Phase III Clinical Trial (BABY HUG) is a double-blind, placebo-controlled trial to assess efficacy of hydroxyurea in preventing organ damage in young children with sickle cell anemia.

PROCEDURES: Enrolled infants were subjected to parent-supervised fluid deprivation, and urine and serum osmolality were determined.

RESULTS: Of 185 infants age 7.5-17.9 months (mean 13.0 +/- 2.7) and fluid-deprived 7.4 +/- 2.4 hr (range 4-13), 178 had concurrent determinations of urine and serum osmolality. Mean serum osmolality was 286 +/- 6 mOsm/kg H(2)O (range 275-312) and independent of age, height, weight, or duration of fluid deprivation. Urine osmolality (mean 407 +/- 151, range 58-794 mOsm/kg H(2)O) was greater than serum (P < 0.0001) and correlated with duration of fluid deprivation (P = 0.001). Of 142 (77.2%) who concentrated urine, 54 (29.4%) had urine osmolality >500 mOsm/kg H(2)O. Urine osmolality correlated with (99m)Tc-DTPA clearance (P = 0.02) and serum urea nitrogen (P < 0.0001), but not with serum osmolality, gender, age, height, weight, or serum creatinine. Infants able to produce urine with osmolality >500 mOsm/kg H(2)O had higher mean fetal hemoglobin concentrations than did those who could not (P = 0.014).

CONCLUSIONS: Even with often limited fluid deprivation, 77.2% of young infants with sickle cell anemia were able to concentrate urine. Preservation of concentrating ability was associated with higher fetal hemoglobin concentration. Assessment will be repeated after 2 years of hydroxyurea or placebo treatment (ClinicalTrials.gov number, NCT00006400).