The Clinical Use of “Early Weight Loss Nomograms” on Predicting Development of Hypernatremia

<b><i>Objectives:</i></b> To define the safe weight loss percentile threshold for the development of hypernatremia by using the "early weight loss nomograms." <b><i>Methods:</i></b> This retrospective study included exclusively breastfed healthy neonates over 36 weeks' of gestation. (n = 450). Daily percentage points of weight loss were plotted on the "early weight loss nomograms for exclusively breastfed neonates." The presence of hypernatremia was checked if infants lost ≥5% of their birth weight. Hypernatremia was classified as mild, moderate, or severe. The relation of weight loss rates and percentiles to development of hypernatremia was assessed. <b><i>Results:</i></b> The mean gestational age was 38.6 ± 1.3 (36.0-42.3) weeks; the mean birth weight was 3,200 ± 482 g. The mean total weight loss percentage before discharge was 5.9% ± 1.6% (0.5%-17%). The weight loss percentages within first 24 hours were similar in infants born via cesarean section or vaginal delivery (6% ± 1.6% vs. 5.4% ± 1.7%). Mild or moderate hypernatremia developed in 145 infants (32.2%). ROC analyses showed that weight loss of ≥5.5% could predict the development of hypernatremia (AUC = 0.665) and weight loss of ≥7% could predict the development of moderate hypernatremia (AUC = 0.915). Weight loss percentile of ≥75 could also predict the development of hypernatremia with 73% sensitivity and 46% specificity (AUC = 0.622). <b><i>Conclusion:</i></b> To the best of our knowledge, this is the first study to evaluate the relationship between weight loss nomogram percentiles and the development of hypernatremia. Even if the weight loss is within the defined acceptable normal ranges and percentiles, hypernatremia may develop if the weight loss is greater than the 75^th percentile values.