391 A Reference Curve for Relative Weight Loss for Breast-Fed Infants to Detect Hypernatraemic Dehydration

Abstract

BACKGROUND/AIMS: To construct a reference growth chart for breast-fed infants between postnatal day 2 and 11 and to assess its validity in detecting infants with hypernatraemic dehydration. The participants are 1,544 healthy (exclusively) breast-fed infants with 3,075 measurements born during 2002 in three primary care midwife practices in the Netherlands and 83 cases of breast-fed infants with hypernatraemic dehydration obtained by a search of the literature. METHODS: Outcome measure was relative weight loss (weight loss compared to birth weight in %). A reference chart for relative weight loss was obtained by the LMS method, in which centiles are estimated by the Box-Cox power (L-curve), the median (M-curve) and the coefficient of variation (S-curve). RESULTS: The 0.6 centile (= -2.5 SDS) is -11.1% (2 days), -11.9% (3 days), -11.8% (4 days), -11.3% (5 days), -11.0% (6 days), -10.6% (7 days), -10.2% (8 days), -9.8% (9 days), -9.6% (10 days) and -9.5% (11 days). This centile is used as a test to detect children at risk of hypernatraemic dehydration. The test is considered positive if a breast-fed child's relative weight loss decreases below -2.5 SDS and negative if it stays above. Sensitivity (percentage of infants with hypernatraemic dehydration with a positive test) is 86%. Specificity is by definition 99.4%. Positive predictive value is 9.3%, assuming a prevalence of 7.1 per 10,000 breast-fed infants. Cases with a negative test have a mean plasma sodium concentration of 153 mmol/l and cases with a positive test have a mean sodium concentration of 163 mmol/l. CONCLUSIONS: A growth chart for relative weight loss for breast-fed infants in the first days after birth can be helpful to detect infants at risk of hypernatraemic dehydration.