Effect of increased enteral protein intake on plasma and urinary urea concentrations in preterm infants born at < 32 weeks gestation and < 1500 g birth weight enrolled in a randomized controlled trial - a secondary analysis.
BACKGROUND
Feeding breast milk is associated with reduced morbidity and mortality, as well as improved neurodevelopmental outcome but does not meet the high nutritional requirements of preterm infants. Both plasma and urinary urea concentrations represent amino acid oxidation and low concentrations may indicate insufficient protein supply. This study assesses the effect of different levels of enteral protein on plasma and urinary urea concentrations and determines if the urinary urea-creatinine ratio provides reliable information about the protein status of preterm infants.


METHODS
Sixty preterm infants (birthweight < 1500 g; gestational age < 32 weeks) were enrolled in a randomized controlled trial and assigned to either a lower-protein group (median protein intake 3.7 g/kg/d) or a higher-protein group (median protein intake 4,3 g/kg/d). Half the patients in the higher-protein group received standardized supplementation with a supplement adding 1.8 g protein/100 ml milk, the other half received individual supplementation depending on the respective mother's milk macronutrient content. Plasma urea concentration was determined in two scheduled blood samples (BS1; BS2); urinary urea and creatinine concentrations in weekly spot urine samples.


RESULTS
The higher-protein group showed higher plasma urea concentrations in both BS1 and BS2 and a higher urinary urea-creatinine-ratio in week 3 and 5-7 compared to the lower-protein group. In addition, a highly positive correlation between plasma urea concentrations and the urinary urea-creatinine-ratio (p < 0.0001) and between actual protein intake and plasma urea concentrations and the urinary urea-creatinine-ratio (both p < 0.0001) was shown.


CONCLUSIONS
The urinary urea-creatinine-ratio, just like plasma urea concentrations, may help to estimate actual protein supply, absorption and oxidation in preterm infants and, additionally, can be determined non-invasively. Further investigations are needed to determine reliable cut-off values of urinary urea concentrations to ensure appropriate protein intake.


TRIAL REGISTRATION
Clinicaltrials.gov; NCT01773902 registered 15 January 2013, retrospectively registered.
['Mathes|Michaela|M|0000-0001-8737-1821', 'Maas|Christoph|C|', 'Bleeker|Christine|C|', 'Vek|Julia|J|', 'Bernhard|Wolfgang|W|', 'Peter|Andreas|A|', 'Poets|Christian F|CF|', 'Franz|Axel R|AR|']
D001903:Bottle Feeding D003404:Creatinine D004044:Dietary Proteins D005260:Female D005527:Food, Fortified D005865:Gestational Age D006801:Humans D007231:Infant, Newborn D007234:Infant, Premature D019102:Infant, Very Low Birth Weight D008297:Male D008895:Milk, Human
Urea concentration Nutrition Protein supply Supplementation Enteral feeding Infant, newborn Infant, premature Milk, human Targeted fortification Very low birth weight infant