Urinary and serum electrolytes in untreated black and white hypertensives. Veterans Administration Cooperative Study Group on Antihypertensive Agents.

Twenty-four hour urinary excretion of sodium (Na), potassium (K), Na/K ratio and creatinine (Cr), serum Cr, Na, and K, and plasma renin activity (PRA) were evaluated in 623 untreated hypertensive men. Blacks (n = 407) and whites (n = 216) were similar in weight, heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), 24-hour urine Cr excretion, and Cr clearance. Twenty-four hour urine Na excretion was the same in blacks and whites, but whites excreted 62% more K than blacks: 73 +/- 41 (mean +/- SD) vs 45 +/- 40 mEq/24h (p less than 0.001). Urinary Na/K ratio was 4.51 +/- 2.18 in blacks and 2.85 +/- 1.40 in whites (p less than 0.001). Serum K and PRA were also lower in blacks. Serum and urine Na/K ratios, serum Na and age were positively associated with SBP; serum K and PRA were negatively associated with SBP. Serum Na/K ratio, heart rate and weight were positively associated with DBP; serum K was weakly negatively associated with DBP. The racial difference in urinary K excretion and serum K is believed to reflect a difference in dietary K intake between blacks and whites. This difference may be an important factor in the greater prevalence of hypertension among blacks.