Evaluation of salt supplementation in CF infants.
BACKGROUND
CF infants may be at increased risk of sodium depletion which may lead to impaired growth. The objective of this study was to evaluate their sodium supplementation requirements.


METHODS
Ten CF infants had serial measurements of weight and plasma/urine sodium and creatinine. Sodium supplementation was adjusted with the aim of maintaining fractional excretion (FENa) between 0.5% and 1.5% and urinary sodium > 10 mmol/L.


RESULTS
Urine sodium:creatinine (UNa:Cr) ratio strongly correlated with FENa [UNa:Cr (mmol/mmol)=35.0 x FENa (r=0.99)]. The FENa target range corresponded to UNa:Cr 17-52 mmol/mmol. All infants required sodium supplementation to achieve UNa:Cr > 17 mmol/mmol. Sodium supplement requirements (mean+/-SD) at ages 0-3, 3-6, 6-9 and 9-12 months were 1.9+/-0.5, 1.8+/-0.8, 1.9+/-0.9 and 0.8+/-0.4 mmol/kg/d. No infant required calorie supplementation to achieve expected weight gain.


CONCLUSIONS
Using current UK guidelines, many cases of sodium depletion may be overlooked. Some infants require more than the recommended 1-2 mmol/kg/d. UNa:Cr ratio is a useful non-invasive measure to monitor sodium supplementation.