Continuous urine collection in the study of vasopressin in the newborn.

We have evaluated the use of urinary vasopressin (AVP) measurements in human newborns to see if urinary AVP excretion is a true reflection of the plasma level. AVP was measured in 37 simultaneously collected plasma and urine samples. The correlation coefficient was 0.8 (p less than 0.001). AVP extracted in duplicate from six urine samples was measured by bioassay and radioimmunoassay. The correlation coefficient was 0.85 (p less than 0.05). To facilitate long-term urine collection we have developed a urine collecting tray to fit a standard incubator or cot. Urinary AVP as measured in 24-hour urine collections in 37 normal infants. AVP excretion was higher in the first 48 h of life than subsequently. Continuous 4-hour urine collections were made in 1 sick infant to assess AVP excretion when urine flow is variable.