Primary aldosteronism is an important cause of secondary hypertension though its diagnosis can prove challenging. In normal individuals aldosterone release follows a diurnal pattern, with a morning peak and low levels in the evening. Aldosterone is present in saliva and due to its lipophilic nature it passes into saliva along a concentration gradient. Salivary steroid testing is well established for cortisol and testosterone, but not yet for aldosterone.
We sought to determine the relationship between salivary and serum aldosterone in normotensive individuals and to examine the effect of time of day on salivary aldosterone concentration.
We developed a salivary aldosterone assay by modifying the Siemens Coat-A-Count aldosterone solid phase RIA. Saliva was collected on three occasions during a 24 h period from 100 normotensive volunteers; at 2300 h following 30 min sitting at rest, at 0730 h the next morning while recumbent and at 1200 h after a morning of normal activity. Serum aldosterone was measured to coincide with the saliva sample given at 1200 h. Approval was obtained from the local research ethics committee.
Male to female ratio was 3664, median age 33 years (range 1965), mean blood pressure 118/74 mmHg (S.D.±15/6). Salivary aldosterone at 1200 h correlated strongly with the paired serum aldosterone sample (r=0.78, P<0.01). A repeated measures ANOVA showed a marked difference in mean salivary aldosterone concentration between 1200 and 2300 h (47.3 vs 11.0 pmol/l, P<0.0001).
We have demonstrated that salivary aldosterone correlates well with serum aldosterone at 1200 h and that in normal individuals late night salivary aldosterone is significantly lower than at noon. Salivary sampling was non-invasive and acceptable to subjects. Further studies of salivary aldosterone in hypertensive patients are warranted.