1 State University of New York, Upstate Medical Center
The mean concentration of sodium in serum of a group of normal children in Syracuse, N.Y., in midsummer was 146 meq/l.
The total standard deviation for within-individual variation was 4 meq/l, comprising a laboratory error of ±2.5 meq/l and a "true" within-individual variability of ±3.2 meq/l.
No significant difference between individuals was demonstrated.
Within 90% confidence limits, the maximum chance difference between two successive concentrations of sodium in the serum, whose mean falls within the normal range for means of two samples was found to be 11 meq/l.
Within 95% confidence limits, the maximum chance difference between any two values, duplicate or successive, due to laboratory error was 6.9 meq/l.
The implications of these findings for the interpretation of sodium levels in serum of patients are discussed.