The differential diagnosis of hypernatraemia in children, with ...

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The Diagnosis of Salt Poisoning Leading to Hypematraemia in Children – September 2009 6.2.2 Fractional urinary sodium excretion The fractional urinary sodium excretion (FE Na) is calculated from simultaneous measurement of the blood and urinary sodium and creatinine concentrations 27 , using the following formula: FE Na (%) = U Na x P Cr x 100 U Cr x P Na Where U Na is urinary sodium, P Cr is plasma creatinine, U Cr is urinary creatinine and P Na is plasma sodium. The units of measurement must be the same for the sodium concentrations (although the conversion factor for sodium between mmol/L and mEq/L is 1) and for the creatinine measurements (to convert from mg/dL to μmol/L, multiply by 88.4). Beware also of differences between laboratory reporting using micromol/L in plasma and mmol/L in urine, which are 1,000 times different: these have to be converted to the same units! The FE Na is a reasonable proxy for the sodium excretion rate. 6.2.2.1 Excessive sodium intake There are only reports of 3 cases of excessive sodium intake where fractional sodium excretion was either calculated or could be calculated from the information given in the publication. Details of the three cases are given below: FE Na = 15% 167 (case 1) , aged 20 months, serum sodium 195 mmol/L, salt added to yoghurt. The child received peritoneal dialysis, but details of this were not given. FE Na = 21% 167 (case 2) , aged 7 months, serum sodium 178 mmol/L, rehydration fluid with excessive salt content. The child received a rehydration solution with 40 mmol/L of sodium. FE Na = 9.5% 258 , adult aged 26, deliberate self-harm, serum sodium 188 mmol/L, ingested salt solution. The patient received fluids containing 5% dextrose and 4 grams per litre of saline. None of these patients received intravenous 0.9% saline. 79
The Diagnosis of Salt Poisoning Leading to Hypematraemia in Children – September 2009 6.2.2.2 Healthy children A Medline literature search (available upon request from the College’s Science and Research Department) was conducted to identify any studies of normal values for fractional sodium excretion rates in infants, children or adults; and also of studies reporting fractional sodium excretion rates in children with diarrhoea and dehydration. There are a small number of case series reporting fractional urinary sodium excretions in normal healthy children, in healthy adults, as well as healthy term and preterm infants. Four studies report normal values in healthy children of different ages. These are summarised below: Age No. Mean SD Mean + 2 SD Rossi 283 1 to 14 years 50 0.67 0.37 1.41 Rossi 283 1 to 12 months 8 0.48 0.18 0.85 Assadi 284 6 to 12 months 8 0.4 0.1 0.6 Kalman 285 1 to 13 years 21 1.2 0.3 1.8 Agras 286 0 to 13 years 13 0.78* 1.1 + * median, + maximum The normal ranges vary between the four studies, but numbers are small. In three of the four studies, a group of normal children was investigated for comparison with the subjects of the research. Four publications report the FE Na in well term infants in the first 4 days after birth, and these are summarised below: Postnatal age No. Mean SD Mean + 2 SD Awad H 287 1 day 10 1.13 0.98 3.09 3 days 10 1.48 1.38 4.24 Koo 288 1 st 4 days 6 0.3 0.24 0.78 Aggarwal 289 2 days 25 1.0 0.7 2.4 4 days 25 0.9 0.8 2.5 Andronikou 290
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The Differential Diagnosis of Hyper
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The Diagnosis of Salt Poisoning Lea
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