Background Measurement of aldosterone and/or renin is essential to aid the differential diagnosis of secondary hypertension, guide strategy for therapeutic management of hypertension and assess adequacy of mineralocorticoid replacement. Aim The objective was to establish normative data for aldosterone and renin using the Immunodiagnostic Systems specialty immunoassay system platform in a Caucasian population. Methods Following informed consent, 365 subjects were recruited to this study. Subjects were ambulatory and attended clinic for blood pressure measurement and phlebotomy between the hours of 7:00 and 11:00. Blood pressure was measured according to the 2013 European Society of Hypertension/Cardiology guidelines. The inclusion criteria: age 18 years, BMI <30kg/m(2), non-pregnant, blood pressure <140/90, normal electrolytes and kidney function and not taking prescribed/over the counter medications. Ninety-four subjects were excluded based on these criteria. A total of 271 volunteers (females n=145), aged 18-65 years formed the reference cohort. Blood for aldosterone/renin was collected into ethylenediaminetetraacetic acid specimen tubes. Samples were kept at room temperature and transported within 30min of blood draw to the laboratory for immediate processing (centrifugation, separation and freezing of plasma). Plasma was stored at -20? prior to analysis on the Immunodiagnostic Systems specialty immunoassay system instrument. Results The established reference intervals in an Irish Caucasian population for renin: females: 6.1-62.7mIU/L, males: 9.0-103mIU/L, for aldosterone: females: <138-1179pmol/L, males: <138-670pmol/L, respectively. Conclusion This study demonstrates that reference intervals for aldosterone and renin should be gender specific. These automated immunoassays offer rapid stratification of patients with refractory hypertension and will better facilitate the optimization of therapeutic management.