Serum creatinine concentration, urinary creatinine excretion and creatinine clearance during the first 9 weeks in preterm infants with a birth weight below 1500 g

Little is known about serum creatinine concentration, urinary creatinine excretion and creatinine clearance in preterm infants, The aim of the present study was to establish age related reference values for the first weeks of life in preterm infants with a birth weight < 1500 g. In addition, the possible influence of therapy with dexamethasone, spironolactone and catecholamines was investigated. In 34 patients, serum creatinine, urinary creatinine excretion and creatinine clearance were measured at weeks 1, 2, 3-4, 5-6 and 7-9 of life. Median birth weight was 1225 g (range 730-1495), mean gestational age 29 (range 26-34) weeks. Concentration of creatinine in serum and urine, urinary creatinine excretion per kilogram body weight and creatinine clearance showed a significant correlation with postnatal age. Thus age related reference values as proposed given in the present study are desirable. Median serum creatinine concentration decreased continuously within the first weeks of life: 97 (10-90th percentile: 69-141) in the 1st week, 70 (45-99) in the 2nd week, 57 (39-71) at week 3-4, 51 (42-62) at week 5-6 and 44 (39-48) mu mol/l at week 7-9. Median creatinine output in mu mol/kg body weight was 100 (10-90th percentile: 62-160) in the 1st week, 92 (65-120) in the 2nd week, 79 (52-122) at week 3-4, 89 (68-106) at week 5-6 and 86 (54-109) mu mol/kg/d at week 7-9. Creatinine clearance increased significantly within the first weeks of life. Values were 12.5 (10-90 the percentile: 7-22) in the 1st week, 16 (10-28) in the 2nd week, 20 (11-34) at weeks 3-4, 23 (15-36) at weeks 5-6 and 29 (17-36) ml/min per 1.73 m(2) at weeks 7-9. Therapy with dexamethasone, spironolactone or catecholamines showed no influence on creatinine excretion. Creatinine clearance did not only depend on postnatal age but also on gestational age and on the necessity of mechanical ventilation. These findings indicate a reduced glomerular filtration rate in very immature and severely ill preterm infants. Conclusion It might be necessary to lower dosage of renal excreted drugs in very immature and mechanically ventilated infants according to the creatinine clearance.