title: Usefulness of short-term urine collection in the nutritional monitoring of low birthweight infants.
abstract: To establish adequacy of urine collection times shorter than 24h in the metabolic monitoring of low birthweight infants, we collected urine for 24 h in 39 LBW infants during the third and fourth week of life. All urine voidings over the 24-h period were separately collected, the volume of each sampling and the time of voiding were recorded, and 20% of the volume was removed for pooling. All individual and pooled samples were analysed for total nitrogen, urea and ammonia, alpha-amino nitrogen, creatinine, sodium, potassium, calcium and phosphorus, and for each compound the ratio to 1 mol creatinine was established. Individual sample results were "pooled" to obtain 3-, 6- and 12-h period excretion and than related to the 24-h excretion as measured in the pooled 24-h sample. As the volume of urine obtained in any 6-h collecting period depended on the time of sampling (06:00-12:00 h, 17.5+/-3.1% of total; 12:00-18:00 h, 31.6+/-5.1% of total; 18:00-24:00 h, 25.6+/-3.1% of total; and 0:00-06:00h, 25.3+/-2.9% of total), calculations were based on samples obtained from 18:00 to 06:00 h. The correlation between results of 3- and 24 h-collection periods was weakest, while results of the 6-h collection correlated highly with the total daily excretion (r = between 0.82 and 0.93 for the different compounds) and the correlation was only slightly better when the 12-h collection period was considered. The correlation between the mean molar substrate/creatinine ratio of all individual samples of a 24-h collecting period and the and total daily excretion of the respective substrate was weaker (r = between 0.46 and 0.76 for the different compounds) than the correlation between the results of a 6-h collecting period and the daily excretion is not as stable than in later life. The data indicate that 6-h urine sampling may be sufficient for metabolic monitoring of LBW infants. By contrast, urinary substrate/creatinine ratios are not good markers of the daily excretions of the respective substrate during the first weeks of life.
authors.affiliation: Centre for Infant Nutrition to Prevent Illnesses in Adult Life, Milan, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Boehm
authors.forename: M
authors.initials: M
authors.lastname: Wiener
authors.forename: C
authors.initials: C
authors.lastname: Schmidt
authors.forename: A
authors.initials: A
authors.lastname: Ungethüm
authors.forename: B
authors.initials: B
authors.lastname: Ungethüm
authors.forename: G
authors.initials: G
authors.lastname: Moro
mesh_terms: D000641:Ammonia / Q000652:urine; D000704:Analysis of Variance; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007227:Infant Nutritional Physiological Phenomena / Q000502:physiology*; D007230:Infant, Low Birth Weight / Q000502:physiology*; D007231:Infant, Newborn; D016014:Linear Models; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D009584:Nitrogen / Q000652:urine; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D014508:Urea / Q000652:urine; D014556:Urine / Q000737:chemistry*
chemical_list: D000641:Ammonia; D014508:Urea; D003404:Creatinine; D009584:Nitrogen