The utility of overnight urine collections in assessing compliance with a low sodium intake diet.

To develop methods of estimating sodium intake in free-living persons, we gave normal volunteers mean sodium intakes of 65, 110, and 200 mEq/day. The intake was randomly varied about each mean by an SD of 12.5% daily. Twenty-four-hour and night urinary sodium excretion were measured. Night urinary sodium excretion was also estimated by means of inexpensive quantitative and qualitative chloride titrator strips. The latter required no timed urine collection. A total of three 24-hour urine collections were necessary to differentiate the regimens with 95% accuracy. Three night urinary sodium excretory estimates by the quantitative chloride titrator provided 79% accuracy in identifying the level of dietary sodium intake. By applying the qualitative chloride titrator every other day, the dietary regimens could be differentiated with 95% accuracy. These techniques were not only useful in estimating sodium intake, but also provided a simple means of documenting compliance to sodium restriction. Patients should have no difficulty in applying these methods themselves in a home setting.