Reproducibility of salt sensitivity testing using a dietary approach in essential hypertension

To investigate the reproducibility of salt sensitivity testing using a dietary approach, 30 essential hypertensive patients underwent salt sensitivity testing on an outpatient basis twice with a 6 month interval. At both tests casual and 24-h ambulatory blood pressure (24-h BP) was recorded on habitual diet, then after a 6-day period on a low salt diet (aiming at 50 mmol/day), and finally after a 6-day period on a high salt diet (supplementation with sodium chloride tablets aiming at 250 mmol/day). Subjects showing > or =10% increase in mean BP when changing from low to high dietary salt intake were classified as salt sensitive. Dietary salt intake was assessed as 24-h urinary sodium excretion. Based on 24-h BP recordings eight patients were characterised as salt sensitive (SS) and 22 as salt resistant (SR) in the first test, and three of the initial SS and 15 of the initial SR patients maintained their salt sensitivity status at the second test. Based on casual BP recordings 13 patients were characterised as SS and 17 as SR in the first test, and three of the initial SS and 13 of the initial SR patients maintained their salt sensitivity status at the second test. Thus, salt sensitivity status was reproducible in 60% when using 24-h BP, and in 53% when using casual BP measurements. There was no difference in baseline BP in dietary salt intake between the two tests. In the total study population, no significant correlation was found between the change in casual or 24-h BP during salt repletion in the first and second test. In conclusion casual and 24-h BP response to a 200 mmol/24h change in dietary salt intake is highly individual and varies over time. Characterisation of salt sensitivity using a dietary approach in out-patients is reproducible in only 53-60% of the patients.