Establishment of reference intervals for aldosterone and renin in a Caucasian population using the newly developed Immunodiagnostic Systems specialty immunoassay automated system.

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 <30 kg/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 30 min 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: 6.1-62.7 mIU/L, males: 9.0-103 mIU/L, for aldosterone: females: <138-1179 pmol/L, males: <138-670 pmol/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.

Reference intervals for aldosterone, renin, and the aldosterone-to-renin ratio in the population-based Study of Health in Pomerania (SHIP-1).

The renin-angiotensin-aldosterone system plays a key role in the regulation of human blood pressure. The aldosterone-to-renin ratio (ARR) is widely accepted for screening the primary hyperaldosteronism (PAL). Various cutoffs for positive PAL screening have been defined in patient cohorts from endocrinological referral centers and primary care. However, the distribution of the ARR in the general population is largely unknown. We aim to provide reference ranges for plasma aldosterone concentration (PAC), plasma renin concentration (PRC), and the ARR for the general population of north-east Germany. A cohort of 3 300 subjects participated in the first follow-up of the longitudinal, population-based Study of Health in Pomerania (SHIP). PAC and PRC were measured by radioimmunometric procedures. The reference interval was defined as the central 95% range between the 2.5(th) and 97.5(th) percentiles. A reference population comprising 1,347 healthy subjects was selected. Sex and age-specific (25-54 and 55-74 years) reference ranges are presented. The upper reference limit for the ARR was 14.2 and 20.3 in younger, and 22.4 and 25.5 in older men and women, respectively. Time of blood sampling had no influence on the ARR, while beta blockers, and agents acting on the renin-angiotensin system were associated with higher and lower ARR, respectively. Our upper reference limit for the ARR is clearly lower than previously reported values from studies of hypertensive patients in primary care or hypertension referral centers. We confirm that PAC and PRC are associated with various factors, including sex, age, intake of estrogen, and various antihypertensive medications.

Functional tests for primary aldosteronism: value of captopril suppression.

With the introduction of more simple screening tests such as the aldosterone/renin ratio, the detection rate of primary aldosteronism has increased considerably. Until now, no reference values have been available for reporting the aldosterone/renin ratio using plasma aldosterone values expressed in SI units (pmol/L) and plasma active renin (ng/L) measured by immunoradiometric assay. We studied 153 subjects who had either normal blood pressure, essential hypertension, or primary aldosteronism. Essential hypertensive patients usually have aldosterone/renin (pmol/L/ng/L) ratios below 100, whereas ratios for patients with primary aldosteronism are above 140. Results that fall between 100 and 140 suggest a need for repeat testing. Patients with elevated aldosterone/renin ratios require confirmatory testing to demonstrate nonsuppressive autonomous aldosterone production. To this end, salt loading is widely used, but this approach may be contraindicated in patients with severe hypertension. The captopril suppression test appears as effective as salt loading in confirming a diagnosis of primary aldosteronism. In addition, the captopril test is safe, well tolerated, and cost-effective.

Proteinase activity of human renin preparations: the International Reference Preparation (Renin Standard 68/356).

1. Several commonly used preparations of human renin, including the International Reference Preparation (Renin Standard 68/356), were examined for the presence of contaminating proteinase activity by using a 14C-glycinated bovine haemoglobin substrate assay. 2. All of the human renin preparations tested cleaved haemoglobin even in the presence o di-isopropylfluorophosphate and ethylenediaminetetra-acetate (EDTA). For a given amount of renin activity, varying amounts of proteinase activity were seen. The pH optimum also varied between preparations. 3. Small peptide inhibitors of human renin were not able to inhibit the proteinase activity. Furthermore a diazoacyl reagent and pepstatin, both potent inhibitors of aspartic acid-active site proteinases, were only partially inhibitory. 4. These and other observations suggest that the proteinase activity of the human renin preparations is not due to renin itself, but to contaminating proteinases of different types. Since these enzymes may produce angiotensin I or peptides which may interfere in renin assays, crude preparations of renin which contain proteinase activity, including the International Reference Preparation, should be used with caution or replaced by proteinase-free human renin which can be easily prepared by use of suitable affinity chromatography.

Improvement of renin determination in human plasma using a commonly available renin standard in a radioimmunological method.

UNLABELLED: A new method for the measurement of renin in human plasma is described. The method is based on the introduction of the internationally available renin standard of the Medical Research Council (MRC) London, as a calibration system. Thus, some principal disadvantages of methods expressing results in renin reaction velocity (angiotensin generation rate) only are avoided. Both renins, unknown and standard, react with a sheep substrate preparation and are handled identically throughout the whole procedure including the angiotensin I radioimmunoassay (RIA). The plasma renin concentration (PRC) is given in 10(-6) MRC-renin units (muM/ml). RESULTS: the renin standard is free of angiotensin, angiotensinases, and angiotensinogen; it is stable on storage. Identical enzyme kinetics are shown for both renins. An interference between endogenous and exogenous substrate could be avoided. The potentially harmful influences of proteins from the enzyme incubation mixture of the RIA dose response curve are shown. The use of an angiotensin I calibration system could be omitted. Using a standard renin dilution from 250-0.9 muU/ml also the full biological range is covered. When giving an unrestricted diet the preliminary normal values of PRC are 21.9 +/- 12.6 muU/ml in recumbent and 40.1 +/- 19.8 muU/ml in upright position (n = 16,x +/- s, age 20-35 years). Earlier findings of age-dependency of PRC were confirmed.