A simple field test for assessing salt balance in heat-stressed miners.

A simple colorimetric test for urinary chloride (Fantus test) corrected for urine specific gravity (measured by refractometry) enabled 24-hour urinary sodium excretion rates to be predicted accurately from a single spot sample of urine. In 29 acclimatized miners working in an environment in excess of 40 degrees C, salt-conserving mechanisms, involving renin and aldosterone, were not active until the urinary sodium excretion rate fell below 50 mmol/24 h. A predicted sodium excretion rate greater than 50 mmol/24 h indicates that dietary sodium supplementation is not necessary.