This study aims to evaluate the diagnostic value of the Aldosterone-Renin Ratio (ARR)as a screening test for primary aldosteronism among hypertensives. The test characteristics will be studied. Furthermore, the effect of eplerenone, a selective aldosterone-receptor antagonist will be studied.

Although primary aldosteronism (PA) was formerly seen as a rare cause of hypertension, this condition is now thought to be the commonest cause of secondary hypertension, with the prevalence ranging up to 10-15 % of all hypertensives. Identification of patients with PA allows for specific treatment, for instance unilateral adrenalectomy in case of an aldosterone-producing adenoma or the administration of an aldosterone-receptor antagonist in case of bilateral adrenal hyperplasia.

Since the introduction of the aldosterone-renin ratio (ARR) as a screening tool for PA in 1981, there has been considerable debate about the diagnostic value. The values for aldosterone and renin are highly dependent on many factors, including posture, time of day and medication. Also, the cut-off values for the identification of PA remain controversial.

This study aims to evaluate the test characteristics of the ARR in a population of patients with therapy-resistant hypertension, the dependence of the ARR on medication type and the predictive value on the response on eplerenone, a selective aldosterone-receptor antagonist.

Inclusion Criteria:

• age 18-65 years
• blood pressure above 140 mmHg systolic and above 90 mmHg diastolic
• use of at least 2 antihypertensive drugs

Exclusion Criteria:

• known cause of hypertension, including white-coat hypertension
• severe renal failure (kreat > 200 umol/l)
• BMI above 32 kg/m2
• poorly regulated diabetes mellitus (HbA1C > 8.0 %)
• heart failure
• stroke or myocardial infarction within 6 months before inclusion
• angina pectoris
• pregnancy
• neoplastic disease, within 5 years before inclusion
• alcohol abuse