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Summary

DOI: 10.1373/clinchem.2011.178111

A 5-day-old girl, born at term after an uncomplicated pregnancy, was admitted to the hospital after a routine midwife check showed that she had lost 15% of her original birth weight [6.2 lb (2.83 kg)]. She was being fed normal-term formula milk, and an initial assessment revealed only mild dehydration. The working diagnosis was a feeding problem, and her management plan was to be fed 150 mL/kg formula milk per day with regular monitoring of weight. The patient's serum concentrations of selected analytes were as follows: sodium, 135 mEq/L (135 mmol/L; reference interval, 135–145 mmol/L); potassium, 5.3 mEq/L (5.3 mmol/L; reference interval, 3.5–5.3 mmol/L); and urea, 11.7 mg/dL (4.2 mmol/L; reference interval, 3.5–6.5 mmol/L).

Student Discussion

Student Discussion Document (pdf)

Siba P. Paul,1* Bryony A. Smith,1 Timothy M. Taylor,1 and Joanna Walker2

1 Department of Paediatrics, St. Richard’s Hospital, Chichester, UK; 2 Department of Paediatrics, Queen Alexandra Hospital, Cosham, UK.
* Department of Paediatrics, St. Richard’s Hospital, Spitalfield Lane, Chichester PO19 6SE, UK. Fax 0044-1243-831431 ; E-mail [email protected].

Case Description

A 5-day-old girl, born at term after an uncomplicated pregnancy, was admitted to the hospital after a routine midwife check showed that she had lost 15% of her original birth weight [6.2 lb (2.83 kg)]. She was being fed normal-term formula milk, and an initial assessment revealed only mild dehydration. The working diagnosis was a feeding problem, and her management plan was to be fed 150 mL/kg formula milk per day with regular monitoring of weight. The patient’s serum concentrations of selected analytes were as follows: sodium,135 mEq/L (135 mmol/L; reference interval, 135–145 mmol/L); potassium, 5.3 mEq/L (5.3 mmol/L; reference interval, 3.5–5.3 mmol/L); and urea, 11.7mg/dL (4.2 mmol/L; reference interval, 3.5– 6.5 mmol/L).

Five days after admission, the patient’s weight was unchanged. Her serum analyte concentrations were now as follows: sodium, 128 mEq/L (128 mmol/L); potassium, 6.7 mEq/L (6.7 mmol/L); urea, 5.8 mg/dL (2.1 mmol/L); creatinine, 0.3 mg/dL (28 μmol/L; reference interval, 60–100 μmol/L); and blood glucose, 77.4 mg/dL (4.3 mmol/L; reference interval, 4–7 mmol/L). These findings prompted more-detailed biochemical and endocrine tests. Her bicarbonate concentration was 30 mEq/L (30 mmol/L; reference interval, 24–32 mmol/L), and her chloride concentration was 94 mEq/L (94 mmol/L; reference interval, 95–105 mmol/L). These results yielded an anion gap of 10.7 mmol/L. The urine sodium concentration was 10 mEq/L (10 mmol/L). Further blood results were available 2 days later: plasma renin, 854 mIU/L (reference interval, 4–190 mIU/L in 7 days to 1 year); serum aldosterone, 5786 ng/L (reference interval, 300–2000 ng/L in neonates). The results of blood gas, serum cortisol, ammonia, lactate, urine culture, and urine steroid profile tests were all normal.

Questions to Consider

What are common causes of excess weight loss in a neonate who presents in the first few days of life?
What are the possible explanations for hyponatremia with hyperkalemia in a neonate with excessive weight loss?
What laboratory investigations are appropriate?

Final Publication and Comments

The final published version with discussion and comments from the experts appears in the February 2013 issue of Clinical Chemistry, approximately 3-4 weeks after the Student Discussion is posted.

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