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 creatini ne excretion and creatinine clearance in preterm infants, The aim of t he 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, spi ronolactone and catecholamines was investigated. In 34 patients, serum creatinine, urinary creatinine excretion and creatinine clearance wer e measured at weeks 1, 2, 3-4, 5-6 and 7-9 of life. Median birth weigh t was 1225 g (range 730-1495), mean gestational age 29 (range 26-34) w eeks. Concentration of creatinine in serum and urine, urinary creatini ne excretion per kilogram body weight and creatinine clearance showed a significant correlation with postnatal age. Thus age related referen ce values as proposed given in the present study are desirable. Median serum creatinine concentration decreased continuously within the firs t 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 m ol/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 clearanc e 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 2 nd week, 20 (11-34) at weeks 3-4, 23 (15-36) at weeks 5-6 and 29 (17-3 6) ml/min per 1.73 m(2) at weeks 7-9. Therapy with dexamethasone, spir onolactone or catecholamines showed no influence on creatinine excreti on. Creatinine clearance did not only depend on postnatal age but also on gestational age and on the necessity of mechanical ventilation. Th ese findings indicate a reduced glomerular filtration rate in very imm ature and severely ill preterm infants. Conclusion It might be necessa ry to lower dosage of renal excreted drugs in very immature and mechan ically ventilated infants according to the creatinine clearance.