Continuous Urine Collection in the Study of Vasopressin in the Newborn

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Abstract
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 < 0.001). AVP extracted in duplicate from six urine samples was measured by bioassay and radioimmunoassay. The correlation coefficient was 0.85 (p < 0.05). To facilitate long-term urine collection we have developed a urine collecting tray to fit a standard incubator or cot. Urinary AVP was 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.