The heterogeneity of essential hypertension. Relation between lithium efflux and sodium content of erythrocytes and a family history of hypertension.

The lithium efflux and sodium content of erythrocytes were measured in 75 patients with untreated essential hypertension. The average values of both were higher than those of normotensive control subjects. Values above the range in the controls were found only in patients with a family history of hypertension, and in these the frequency of raised lithium efflux was 76% and of raised sodium content was 36%. Measurement of lithium efflux and sodium content, together with the family history, allows patients with essential hypertension to be categorised into four groups.