This study evaluates how often the self-report of a low sodium (Na) intake is reflected by a low 24-h urinary sodium excretion and examines the influence of incomplete urinary collections on this comparison.


In a study in which 24-h urine collections were obtained for measurement of Na and creatinine excretion, 120 participants were asked whether their Na intake was low, medium, or high. A 24-h urine collection was considered complete if creatinine excretion was ≥20 mg/kg in men or ≥15 mg/kg in women, and incomplete if below those amounts. The kappa statistic was computed to assess the level of agreement between 24-h Na excretion, dichotomized at 100 meq and self-report responses.


Agreement between self-reported and actual Na excretion was poor. The kappa statistic was 0.18 for the total sample, 0.04 for complete collectors, and 0.51 for incomplete collectors, respectively. Overall, 24-h Na excretion exceeded 100 meq among 75% of those reporting an average or high Na intake, but it also exceeded 100 meq among 57% of those reporting a low sodium intake. Further, among those reporting a low sodium intake, Na excretion exceeded 100 meq in 80% of those who submitted a complete collection, but in only 29% of those who submitted an incomplete collection.


These findings suggest that many individuals who report a low salt diet actually excrete ≥100 meq/day. Na intake is also frequently underestimated because many 24-h urine collections are incomplete. Am. J. Hum. Biol., 2012. © 2012 Wiley Periodicals, Inc.