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OS 35-05 MEASUREMENT OF ANGIOTENSIN II AT EQUILIBRIUM IN THE DIAGNOSTIC WORKUP OF PRIMARY ALDOSTERONISM - IMPACT OF PATIENT POSITIONING AND ACE INHIBITOR TREATMENT.

OBJECTIVE
Primary aldosteronism (PA) is a widely under-diagnosed, potentially curable and specifically treatable cause of hypertension. PA screening involves measuring the aldosterone-to-renin-ratio (ARR), but false negative results can occur in the setting of medications, which block the renin-angiotensin system (RAS). Withdrawing RAS blockers from patients with resistant hypertension is not without cardiovascular risk. A novel diagnostic approach, the aldosterone-to-angiotensin-II-ratio (AA2-Ratio), has the potential for less drug interference and improved reliability in PA screening and confirmation of diagnosis.


DESIGN AND METHOD
Serum samples from 80 patients undergoing PA confirmation testing were analyzed. Sampling was performed in a recumbent (7 a.m.) and in an upright (10 a.m.) position before and after 4 days of oral administration of fludrocortisone and salt loading. The concentrations of renin, aldosterone and equilibrium Angiotensin-II were determined and ARR and AA2-Ratios were calculated. The interference of ACE-inhibition with the AA2-Ratio was investigated in healthy volunteers receiving 10 mg enalapril daily for 8 days.


RESULTS
Renin concentration was undetectable in more than 40% of samples, while equilibrium Angiotensin-II was measurable in 98% of all 320 samples analyzed. Angiotensin-II levels were significantly higher in upright collected samples compared to samples collected in a recumbent position. Comparison of the ARR with the AA2-Ratio revealed a significantly larger diagnostic window for the AA2-Ratio. While the ARR was significantly suppressed by ACE-inhibitor treatment, the AA2-Ratio remained unaffected by ACE-inhibition.


CONCLUSIONS
The AA2-Ratio may be superior to the ARR in PA screening among hypertensive patients. Equilibrium Angiotensin-II levels show expected responses to posture and appear to outperform renin concentration as a marker for RAS activation in terms of sensitivity, giving a measurable readout even in clinical states characterized by markedly suppressed RAS activity. The stability of the AA2-Ratio in the presence of ACE-inhibition points to a potential use of the AA2-Ratio PA screening in hypertensive patients without ACE-inhibitor discontinuation.