32 VALIDATION OF “SPOT” URINE ANALYSES IN ASSESSING SODI UM OUTPUT IN INFANTS

Abstract

The urinary sodium concentration(UNa) and sodium/potassium ratio(Na/K)are frequently used to assess sodium status in infants with abnormal sodium losses. However, 24hr urine collection in infants is difficult and prone to error and we therefore studied the validity of using spot urine samples, comparing values for “spot” UNa and Na/K with 24hr urine collections and 24ht fractional sodium excretion(FeNa). Twenty infants(median age 24 ds, ranged 6-150d;mean weight 2.6 kr SD 0.65 kg)were studied, all receiving parenteral or enteral nutrition. Plasma levels of sodium, potassium and creatinine were all within the normal range. Urine was collected using a specially designed metabolic cot. Collections were made at 2 and 4hr, and then regularly during the next 20hrs. One ml aliquotes from the 0-2 and 2-4hr urine collections were analysed separately(spot 1 and spot 2);all remaining urine collected was pooled(24hr urine). - UNa in both spot samples correlated positively and significantly with UNa in 24hr urine(r1= 0.67, p<0.01;r2=0.62, p<0.01), Furthermore, Na/K in both spot urines correlated with Na/K in 24hr urine(r1=0.76,p<0.001;r2=0.78, p<0.00l) and FeNa(r1=0.47, p<0.05;r2=0.61, p<0.01). Conclusion: The sodium concentration and sodium/potassium ratio in spot urines accurately reflect values derived from 24hr urine collection and may be used to assess sodium balance in infants.