Evaluation of the Normal Range of Urinary Sodium Levels in Healthy Newborn Babies

Plain-language summary

Oral sodium supplementation is currently administered in cases of poor weight gain in infants particularly in patients who have undergone gastrointestinal surgical procedures. The decision to start oral supplementation is based on urinary sodium levels although the level at which to start treatment is variable as the range in normal, healthy infants is unknown. This study aims to ascertain the normal range of sodium in urine specimens collected from healthy newborn babies. It is believed that by increasing the level of salt in the intestine, glucose can be more easily be absorbed and therefore weight gain improved. Babies with conditions where they are at risk of salt depletion (i.e. those with a stoma) are currently administered oral sodium supplementation if they are failing to gain weight and have an associated 'low' urinary sodium level. Low levels of urinary sodium are considered to represent a state of low body sodium levels, as the kidneys attempt to reabsorb most of the sodium in the urine before it is excreted. Current practice varies widely as to the level below which treatment should be instigated. Some centres advise below 20 mmol/L (Birmingham Children's Hospital and Nottingham Children's Hospital guidelines), others below 10 mmol/L (University Children's Hospital, Zurich). In Glasgow, babies with poor weight gain are given sodium supplementation if urinary sodium levels are below 40 mmol/L. There are no documented ranges for the levels of urinary sodium in healthy, newborn babies. By determining the reference range of urinary sodium levels in healthy, term babies who are gaining weight appropriately, the investigators hope to be able to have a better understanding about both the level below which supplementation should be considered and the target range that should be aimed for.

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