Sodium-lithium countertransport in erythrocytes of children and adolescents with hypertension.

We have investigated the sodium-lithium countertransport system as a screening test for hypertensive disease in children and adolescents using the method of Canessa et al. [New Engl. J. Med. 302: 772-776, 1980]. The sodium-lithium countertransport in erythrocytes was measured in patients, ages 4-18 years, having essential hypertension or secondary hypertension and compared with age-, weight-, sex- and race-matched normotensive controls. Children and adolescents with essential hypertension possessed a significantly higher erythrocyte sodium-lithium countertransport rate than the normotensive control group (0.39 +/- 0.18, n = 28, vs. 0.22 +/- 0.14 mmol Li/l red cells/h, n = 20, respectively; p less than 0.001). Children with secondary hypertension had intermediate values (0.31 +/- 0.15 mmol Li/l red cells/h; n = 17) which did not differ significantly from values of subjects with essential hypertension or normotensive controls. There was no correlation of counter-transport values with age, sex, or body weight in either hypertensive or normotensive groups. However, white normotensive children had significantly higher countertransport levels compared with black normotensives (0.32 +/- 0.14, n = 10, vs. 0.13 +/- 0.07 mmol Li/l red cells/h, n = 10, respectively; p less than 0.005). Similarly, white children and adolescents with essential hypertension had higher mean countertransport measurements than did black hypertensives (0.42 +/- 0.20, n = 21, vs. 0.27 +/- 0.05 mmol Li/l red cells/h, n = 7, respectively) although this difference did not reach statistical significance (p less than 0.1). Although children and adolescents with essential hypertension had a significant elevation of sodium-lithium countertransport when compared to normotensives, the large degree of overlap of countertransport values in these two groups, as well as the intermediate values of children with secondary hypertension, limits the usefulness of the sodium-lithium countertransport as a screening test for essential hypertension in this population. Taking into account the influence of racial differences on the countertransport assay does not sufficiently improve the discriminatory value of the test to render it clinically useful.