Original Article
Measurement of plasma renin concentration instead of plasma renin activity decreases the positive aldosterone-to-renin ratio tests in treated patients with essential hypertension Chiara Lonati a, Niccolo ` Bassani b, Anna Gritti a, Elia Biganzoli b, and Alberto Morganti a
Background: The plasma aldosterone-to-renin ratio (ARR) for the diagnosis of primary aldosteronism is normally calculated with plasma renin activity (PRA) as denominator. However, new direct renin assays that measure plasma renin concentration (PRC) are progressively replacing PRA because these are faster, simpler, and more reproducible. Objective: To assess whether the calculation of ARR with a direct assay (ARRD, ng/dl/mU/l) instead of PRA (ARRP, ng/dl/ng/ml/h) affects the rate of positive tests in patients on liberal antihypertensive treatment. Design and participants: PRA, PRC, and plasma aldosterone concentration (PAC) were measured in 88 patients with essential hypertension, both in the supine position and after 60 min of active standing while on treatment with a variety of antihypertensive medications. The same measurements were carried out, for comparison, in 10 patients with proven aldosterone-producing adenoma. Setting: Single center, outpatient hypertension clinic in a tertiary care hospital. Results: In patients with essential hypertension, median ARRP was 12 (range 0–71) in the supine position and 13 (range 0–80) after standing. The corresponding values of ARRD were 0.4 (range 0.01–3) and 0.5 (range 0.02–7.8). Between ARRP and ARRD, there was a linear, highly significant relationship both in supine and standing position (r ¼ 0.88 and r ¼ 0.92, respectively). Using as threshold of normalcy for ARRP a value less than 30, as it is recommended by guidelines, there were 13 (15%) and 18 (20%) false positives, respectively in supine and standing position, whereas with the threshold of 3.7 for ARRD, there were no false positives in recumbent position and four (5%) after standing. Accordingly, the specificity of ARRP was 0.85 and 0.78 and that of ARRD 1 and 0.95. In 10 patients with primary aldosteronism, median supine ARRP was 298 (range 48–1222) and ARRD 34 (range 2.8–244). Among these patients, no false negatives were found with ARRP and just one with ARRD. Conclusion: The rate of positive tests calculating ARR with PRC is lower than with PRA, the lower rate being found in
patients studied in the recumbent position and apparently it is not affected by ongoing antihypertensive treatment. Keywords: aldosterone-to-renin ratio, plasma renin activity, plasma renin concentration, primary hyperaldosteronism Abbreviations: ACEI, angiotensin-converting enzyme inhibitors; APA, aldosterone-producing adenoma; ARB, angiotensin receptor blocker; ARR, aldosterone-renin ratio; ARRD, ARR calculated with PRC (direct assay); ARRP, ARR calculated with PRA (enzymatic assay); PAC, plasma aldosterone concentration; PRA, plasma renin activity; PRC, plasma renin concentration; RAS, renin–angiotensin system
INTRODUCTION
P
rimary aldosteronism produced either by an aldosterone-producing adenoma (APA) or by adrenal hyperplasia is characterized by elevated plasma levels of aldosterone and suppressed renin secretion. Not surprisingly then, the calculation of the aldosterone-to-renin ratio (ARR) was introduced already 30 years ago as a convenient screening test for the diagnosis of primary aldosteronism [1]. However, the use of ARR has been limited until recent years when it became clear that primary aldosteronism is a much more frequent cause of hypertension than previously suspected [2]. Whether or not we are actually facing an ‘epidemic’ of primary
Journal of Hypertension 2014, 32:627–634 a Department of Internal Medicine and Hypertension Center, Ospedale San Giuseppe, Istituto Ricovero e Cura a Carattere Scientifico (IRCCS) Multimedica, Department of Clinical Sciences and Community Health and bUnit of Medical Statistics, Biometry and Bioinformatics, Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
Correspondence to Professor Alberto Morganti, Department of Internal Medicine, Ospedale San Giuseppe, Via San Vittore 12, 20121 Milan, Italy. Tel: +39 02 8599 4494; fax: +39 03 8599 4157; e-mail: [email protected] This paper was accepted for poster presentation at the 23rd European Meeting on Hypertension and Cardiovascular Protection, Milan, 14–17 June 2013. Received 3 June 2013 Accepted 13 November 2013 J Hypertens 32:627–634 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. DOI:10.1097/HJH.0000000000000076
Journal of Hypertension
www.jhypertension.com
627
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Lonati et al.
aldosteronism [3,4], it is a matter of fact that the evaluation of ARR has progressively gained popularity for at least two additional reasons. First, it is that measurement of aldosterone and renin jointly is believed to be a more reliable index of primary aldosteronism than either factor alone [5,6]. Second, more important, it is that an elevated ARR is associated with unfavorable cardiovascular and renal outcomes not only in patients with primary aldosteronism [7,8], but also in those with essential hypertension [9–11]. Yet, an extensive application of ARR testing to the general population of hypertensive patients encounters a number of practical and methodological obstacles [12]. That of major concern for clinicians is the recommendation by the Endocrine Society Guidelines [13] of withdrawing from patients’ treatment all medications that may interfere with the production and release of renin and aldosterone [namely, b-blockers and renin–angiotensin system (RAS) antagonists including antagonists of mineraloreceptor] and the substitution with drugs like calcium antagonists and a-blockers that minimally affect ARR. In particular, b-blockers, lowering renin to a greater extent than aldosterone [14], can cause false-positive ARR, whereas RAS antagonists because of the concomitant effect of increasing renin and lowering aldosterone can generate false-negative ARR. However, treatment adjustment can be accompanied by serious side-effects. Indeed, in a recent study [15], the full adherence to guidelines recommendations was possible only in 26 of 50 patients and in three of them caused severe cardiac disorders requiring hospitalization. Another confounding factor in ARR determination is represented by body posture [12]. Recumbent, sitting and upright positions are used by the investigators according to their own protocols making the results hardly comparable. Finally, in many laboratories, new assays that measure renin as mass concentration, the so-called direct renin assays, are progressively replacing the traditional plasma renin activity (PRA) assay. Recent comparative studies have shown that the reproducibility of plasma renin concentration (PRC) among laboratories is higher than that of PRA [16]. Moreover, measurement of PRC is faster, methodologically simpler and results, being independent of angiotensinogen concentration, can be calibrated against an International Reference Standard. Thus, our study had the goal of comparing how the calculation of ARR with PRC instead of PRA affects the rate of false positives, that is, the specificity of this test, in patients while on their original antihypertensive treatment and studied both in supine position and after 1 h of active standing. For comparison, the same evaluation was carried out in a small group of patients with primary aldosteronism.
PATIENTS AND METHODS Patients Eighty-eight hypertensive patients (50 men, 33 women, aged 13–88 years) referred to the outpatient clinic of our hospital for diagnostic workup participated in the study. At the time of blood collection, 12 patients were off treatment, whereas the remaining 76 were on a variety of antihypertensive medications taken as monotherapy or in 628
www.jhypertension.com
combination. In particular, 44 were on treatment with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs), comprehensively referred as RAS antagonists, 18 were on b-adrenoreceptor blockers (in 12 cases in combination with ACEIs or ARBs), 24 were on diuretics, and 31 on calcium antagonists. The mean values of SBP and DBP at the time of the outpatient visit were 153 4/92 2 mmHg. Mean supine plasma potassium levels were 4.3 0.1 mEq/l. In these 88 patients, primary aldosteronism was excluded on the basis of the following criteria: PRA values after the postural stimulus greater than in recumbent position; and imaging investigations (abdominal ultrasound, computed tomography, or magnetic resonance) negative for renal or adrenal abnormalities. Ten patients (six men and four women, aged 21– 66 years) with APA were also studied, before undergoing adrenalectomy, while in the supine position; four of them were on treatment with RAS antagonists. Plasma potassium levels ranged from 2.3 to 4.3 mEq/l. In these patients, the diagnosis of primary aldosteronism was retrospectively confirmed by the histological findings and by the improved blood pressure control in response to the surgical removal of the affected adrenal gland.
Biochemical measurements Blood for measurement of PRA (ng/ml per h), PRC (mU/l), and plasma aldosterone (PAC, ng/dl) was collected from an antecubital vein between 0800 and 1200 h with patients in the supine position at least for 45 min and again after 60 min of active standing. Samples were collected in potassium ethilendiaminotetracetic acid tubes and processed at room temperature until centrifugation, carried out for 15 min. After cells removal, plasmas were rapidly frozen and kept at 208C up to the time of dosage. PRA was measured with a commercial kit (REN-CTK; DiaSorin, Saluggia, Italy), which has been previously validated [17]. In brief, after rapid thawing, 500 ml aliquots of duplicate plasmas were adjusted to pH 6.0 by adding a mixture containing citrate buffer and phenylmethylsulfonyl fluoride as angiotensinase inhibitor and incubated at 378C and 48C (blanks) for 90 min. After incubation, the radioimmunoassay was performed and the concentration of generated angiotensin I calculated by extrapolation of a standard curve with the lowest calibrator at 0.3 ng/ml of angiotensin I. The final value of PRA was calculated with blank subtraction. The functional sensitivity of the assay is set at 0.2 ng/ml per h for values within the working range (from 0.2 to 50 ng/ml per h). The interassay and intraassay variability provided by the manufacturer varies from 7.7 to 11.5% and from 7.5 to 9.9%, respectively for levels ranging from 2.3 to 15.6 ng/ml per h. PRC was measured in a fully automated chemiluminescent analyzer (LIAISON) with reagents provided by DiaSorin (LIAISON Direct Renin Assay; DiaSorin). The method has been described elsewhere in detail [18]. In brief, renin is sandwiched between a capture antibody that recognizes both renin and prorenin adsorbed on paramagnetic particles and a detection isoluminol-labeled antibody specific for renin. After a deliberate short time incubation (30 min), aimed at limiting prorenin activation during the Volume 32 Number 3 March 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Enzymatic vs. direct renin assay for aldosterone-to-renin ratio
determination, starter reagents are added to the mixture to induce the flashing chemiluminescent reaction. The emitted light expressed in relative light units is proportional to the level of renin and reported in mU/l. The final values of PRC are calculated with a two-point working curve adjusted against a stored master curve, the assay being calibrated against the WHO Reference Renin Standard. The functional sensitivity is 2.0 mU/l for values comprised within the working range (from 2 to 500 mU/l) and the interassay and intraassay variability varies from 5.2 to 10% and from 1.2 to 3.7%. PAC was measured by radioimmunoassay with a commercial kit (ALDOCTK-2; DiaSorin). A total of 200 ml of plasma and 500 ml of the tracer (125I-aldosterone) are incubated for 18–22 h with a solid phase rabbit antialdosterone antibody. At the end of the incubation after removal of supernatant, the concentration of aldosterone is calculated by extrapolation of a standard curve with five calibrators. The lower limit of detection of the method is 1 ng/dl with an analytical interval comprised between 1 and 100 ng/dl and the interassay and intraassay variabilities vary from 7 to 4.3% and from 5.3 to 1.7%, respectively.
Aldosterone-to-renin ratio calculation ARR was calculated with aldosterone as numerator expressed in ng/dl and PRA or PRC as denominator expressed, respectively, in ng/ml per h and mU/l. Accordingly, the ratios calculated with the enzymatic and direct assays are reported here, respectively, as ARRP and ARRD.
Statistical analysis Comparison of PRA, PRC, PAC, ARRP, and ARRD was performed via the nonparametric Wilcoxon test for dealing with nonnormality data. Bland–Altman plots modified to account for nonconstant bias were applied to compare supine and standing ARRP and ARRD using R package MethComp [19]. Correlations between ARRP and ARRD were evaluated with the Spearman rank correlation coefficient, and 95% confidence intervals were estimated using a nonparametric bootstrap. The relationship between ARRP and ARRD was also evaluated using the Passing–Bablok regression on log-transformed data [20]. All analyses were performed using R software version 3.0.0 [21].
RESULTS Median supine and standing values of PRA, PRC, and PAC in the 88 essential hypertensive patients are reported in
Table 1. In the 44 patients on RAS antagonists, median PRA and PRC were higher and PAC significantly lower in the two positions than in the other 44 patients not on treatment with these medications (respectively 0.8 vs. 0.5 and 1.7 vs. 1.1 ng/ml per h for PRA, 19.7 vs. 15.9 and 31.8 vs. 27.2 mU/l for PRC, 5.7 vs. 9.4 and 16.9 vs. 22.7 ng/dl for PAC, P
Measurement of plasma renin concentration instead of plasma renin activity decreases the positive aldosterone-to-renin ratio tests in treated patients with essential hypertension Chiara Lonati a, Niccolo ` Bassani b, Anna Gritti a, Elia Biganzoli b, and Alberto Morganti a
Background: The plasma aldosterone-to-renin ratio (ARR) for the diagnosis of primary aldosteronism is normally calculated with plasma renin activity (PRA) as denominator. However, new direct renin assays that measure plasma renin concentration (PRC) are progressively replacing PRA because these are faster, simpler, and more reproducible. Objective: To assess whether the calculation of ARR with a direct assay (ARRD, ng/dl/mU/l) instead of PRA (ARRP, ng/dl/ng/ml/h) affects the rate of positive tests in patients on liberal antihypertensive treatment. Design and participants: PRA, PRC, and plasma aldosterone concentration (PAC) were measured in 88 patients with essential hypertension, both in the supine position and after 60 min of active standing while on treatment with a variety of antihypertensive medications. The same measurements were carried out, for comparison, in 10 patients with proven aldosterone-producing adenoma. Setting: Single center, outpatient hypertension clinic in a tertiary care hospital. Results: In patients with essential hypertension, median ARRP was 12 (range 0–71) in the supine position and 13 (range 0–80) after standing. The corresponding values of ARRD were 0.4 (range 0.01–3) and 0.5 (range 0.02–7.8). Between ARRP and ARRD, there was a linear, highly significant relationship both in supine and standing position (r ¼ 0.88 and r ¼ 0.92, respectively). Using as threshold of normalcy for ARRP a value less than 30, as it is recommended by guidelines, there were 13 (15%) and 18 (20%) false positives, respectively in supine and standing position, whereas with the threshold of 3.7 for ARRD, there were no false positives in recumbent position and four (5%) after standing. Accordingly, the specificity of ARRP was 0.85 and 0.78 and that of ARRD 1 and 0.95. In 10 patients with primary aldosteronism, median supine ARRP was 298 (range 48–1222) and ARRD 34 (range 2.8–244). Among these patients, no false negatives were found with ARRP and just one with ARRD. Conclusion: The rate of positive tests calculating ARR with PRC is lower than with PRA, the lower rate being found in
patients studied in the recumbent position and apparently it is not affected by ongoing antihypertensive treatment. Keywords: aldosterone-to-renin ratio, plasma renin activity, plasma renin concentration, primary hyperaldosteronism Abbreviations: ACEI, angiotensin-converting enzyme inhibitors; APA, aldosterone-producing adenoma; ARB, angiotensin receptor blocker; ARR, aldosterone-renin ratio; ARRD, ARR calculated with PRC (direct assay); ARRP, ARR calculated with PRA (enzymatic assay); PAC, plasma aldosterone concentration; PRA, plasma renin activity; PRC, plasma renin concentration; RAS, renin–angiotensin system
INTRODUCTION
P
rimary aldosteronism produced either by an aldosterone-producing adenoma (APA) or by adrenal hyperplasia is characterized by elevated plasma levels of aldosterone and suppressed renin secretion. Not surprisingly then, the calculation of the aldosterone-to-renin ratio (ARR) was introduced already 30 years ago as a convenient screening test for the diagnosis of primary aldosteronism [1]. However, the use of ARR has been limited until recent years when it became clear that primary aldosteronism is a much more frequent cause of hypertension than previously suspected [2]. Whether or not we are actually facing an ‘epidemic’ of primary
Journal of Hypertension 2014, 32:627–634 a Department of Internal Medicine and Hypertension Center, Ospedale San Giuseppe, Istituto Ricovero e Cura a Carattere Scientifico (IRCCS) Multimedica, Department of Clinical Sciences and Community Health and bUnit of Medical Statistics, Biometry and Bioinformatics, Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
Correspondence to Professor Alberto Morganti, Department of Internal Medicine, Ospedale San Giuseppe, Via San Vittore 12, 20121 Milan, Italy. Tel: +39 02 8599 4494; fax: +39 03 8599 4157; e-mail: [email protected] This paper was accepted for poster presentation at the 23rd European Meeting on Hypertension and Cardiovascular Protection, Milan, 14–17 June 2013. Received 3 June 2013 Accepted 13 November 2013 J Hypertens 32:627–634 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. DOI:10.1097/HJH.0000000000000076
Journal of Hypertension
www.jhypertension.com
627
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Lonati et al.
aldosteronism [3,4], it is a matter of fact that the evaluation of ARR has progressively gained popularity for at least two additional reasons. First, it is that measurement of aldosterone and renin jointly is believed to be a more reliable index of primary aldosteronism than either factor alone [5,6]. Second, more important, it is that an elevated ARR is associated with unfavorable cardiovascular and renal outcomes not only in patients with primary aldosteronism [7,8], but also in those with essential hypertension [9–11]. Yet, an extensive application of ARR testing to the general population of hypertensive patients encounters a number of practical and methodological obstacles [12]. That of major concern for clinicians is the recommendation by the Endocrine Society Guidelines [13] of withdrawing from patients’ treatment all medications that may interfere with the production and release of renin and aldosterone [namely, b-blockers and renin–angiotensin system (RAS) antagonists including antagonists of mineraloreceptor] and the substitution with drugs like calcium antagonists and a-blockers that minimally affect ARR. In particular, b-blockers, lowering renin to a greater extent than aldosterone [14], can cause false-positive ARR, whereas RAS antagonists because of the concomitant effect of increasing renin and lowering aldosterone can generate false-negative ARR. However, treatment adjustment can be accompanied by serious side-effects. Indeed, in a recent study [15], the full adherence to guidelines recommendations was possible only in 26 of 50 patients and in three of them caused severe cardiac disorders requiring hospitalization. Another confounding factor in ARR determination is represented by body posture [12]. Recumbent, sitting and upright positions are used by the investigators according to their own protocols making the results hardly comparable. Finally, in many laboratories, new assays that measure renin as mass concentration, the so-called direct renin assays, are progressively replacing the traditional plasma renin activity (PRA) assay. Recent comparative studies have shown that the reproducibility of plasma renin concentration (PRC) among laboratories is higher than that of PRA [16]. Moreover, measurement of PRC is faster, methodologically simpler and results, being independent of angiotensinogen concentration, can be calibrated against an International Reference Standard. Thus, our study had the goal of comparing how the calculation of ARR with PRC instead of PRA affects the rate of false positives, that is, the specificity of this test, in patients while on their original antihypertensive treatment and studied both in supine position and after 1 h of active standing. For comparison, the same evaluation was carried out in a small group of patients with primary aldosteronism.
PATIENTS AND METHODS Patients Eighty-eight hypertensive patients (50 men, 33 women, aged 13–88 years) referred to the outpatient clinic of our hospital for diagnostic workup participated in the study. At the time of blood collection, 12 patients were off treatment, whereas the remaining 76 were on a variety of antihypertensive medications taken as monotherapy or in 628
www.jhypertension.com
combination. In particular, 44 were on treatment with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs), comprehensively referred as RAS antagonists, 18 were on b-adrenoreceptor blockers (in 12 cases in combination with ACEIs or ARBs), 24 were on diuretics, and 31 on calcium antagonists. The mean values of SBP and DBP at the time of the outpatient visit were 153 4/92 2 mmHg. Mean supine plasma potassium levels were 4.3 0.1 mEq/l. In these 88 patients, primary aldosteronism was excluded on the basis of the following criteria: PRA values after the postural stimulus greater than in recumbent position; and imaging investigations (abdominal ultrasound, computed tomography, or magnetic resonance) negative for renal or adrenal abnormalities. Ten patients (six men and four women, aged 21– 66 years) with APA were also studied, before undergoing adrenalectomy, while in the supine position; four of them were on treatment with RAS antagonists. Plasma potassium levels ranged from 2.3 to 4.3 mEq/l. In these patients, the diagnosis of primary aldosteronism was retrospectively confirmed by the histological findings and by the improved blood pressure control in response to the surgical removal of the affected adrenal gland.
Biochemical measurements Blood for measurement of PRA (ng/ml per h), PRC (mU/l), and plasma aldosterone (PAC, ng/dl) was collected from an antecubital vein between 0800 and 1200 h with patients in the supine position at least for 45 min and again after 60 min of active standing. Samples were collected in potassium ethilendiaminotetracetic acid tubes and processed at room temperature until centrifugation, carried out for 15 min. After cells removal, plasmas were rapidly frozen and kept at 208C up to the time of dosage. PRA was measured with a commercial kit (REN-CTK; DiaSorin, Saluggia, Italy), which has been previously validated [17]. In brief, after rapid thawing, 500 ml aliquots of duplicate plasmas were adjusted to pH 6.0 by adding a mixture containing citrate buffer and phenylmethylsulfonyl fluoride as angiotensinase inhibitor and incubated at 378C and 48C (blanks) for 90 min. After incubation, the radioimmunoassay was performed and the concentration of generated angiotensin I calculated by extrapolation of a standard curve with the lowest calibrator at 0.3 ng/ml of angiotensin I. The final value of PRA was calculated with blank subtraction. The functional sensitivity of the assay is set at 0.2 ng/ml per h for values within the working range (from 0.2 to 50 ng/ml per h). The interassay and intraassay variability provided by the manufacturer varies from 7.7 to 11.5% and from 7.5 to 9.9%, respectively for levels ranging from 2.3 to 15.6 ng/ml per h. PRC was measured in a fully automated chemiluminescent analyzer (LIAISON) with reagents provided by DiaSorin (LIAISON Direct Renin Assay; DiaSorin). The method has been described elsewhere in detail [18]. In brief, renin is sandwiched between a capture antibody that recognizes both renin and prorenin adsorbed on paramagnetic particles and a detection isoluminol-labeled antibody specific for renin. After a deliberate short time incubation (30 min), aimed at limiting prorenin activation during the Volume 32 Number 3 March 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Enzymatic vs. direct renin assay for aldosterone-to-renin ratio
determination, starter reagents are added to the mixture to induce the flashing chemiluminescent reaction. The emitted light expressed in relative light units is proportional to the level of renin and reported in mU/l. The final values of PRC are calculated with a two-point working curve adjusted against a stored master curve, the assay being calibrated against the WHO Reference Renin Standard. The functional sensitivity is 2.0 mU/l for values comprised within the working range (from 2 to 500 mU/l) and the interassay and intraassay variability varies from 5.2 to 10% and from 1.2 to 3.7%. PAC was measured by radioimmunoassay with a commercial kit (ALDOCTK-2; DiaSorin). A total of 200 ml of plasma and 500 ml of the tracer (125I-aldosterone) are incubated for 18–22 h with a solid phase rabbit antialdosterone antibody. At the end of the incubation after removal of supernatant, the concentration of aldosterone is calculated by extrapolation of a standard curve with five calibrators. The lower limit of detection of the method is 1 ng/dl with an analytical interval comprised between 1 and 100 ng/dl and the interassay and intraassay variabilities vary from 7 to 4.3% and from 5.3 to 1.7%, respectively.
Aldosterone-to-renin ratio calculation ARR was calculated with aldosterone as numerator expressed in ng/dl and PRA or PRC as denominator expressed, respectively, in ng/ml per h and mU/l. Accordingly, the ratios calculated with the enzymatic and direct assays are reported here, respectively, as ARRP and ARRD.
Statistical analysis Comparison of PRA, PRC, PAC, ARRP, and ARRD was performed via the nonparametric Wilcoxon test for dealing with nonnormality data. Bland–Altman plots modified to account for nonconstant bias were applied to compare supine and standing ARRP and ARRD using R package MethComp [19]. Correlations between ARRP and ARRD were evaluated with the Spearman rank correlation coefficient, and 95% confidence intervals were estimated using a nonparametric bootstrap. The relationship between ARRP and ARRD was also evaluated using the Passing–Bablok regression on log-transformed data [20]. All analyses were performed using R software version 3.0.0 [21].
RESULTS Median supine and standing values of PRA, PRC, and PAC in the 88 essential hypertensive patients are reported in
Table 1. In the 44 patients on RAS antagonists, median PRA and PRC were higher and PAC significantly lower in the two positions than in the other 44 patients not on treatment with these medications (respectively 0.8 vs. 0.5 and 1.7 vs. 1.1 ng/ml per h for PRA, 19.7 vs. 15.9 and 31.8 vs. 27.2 mU/l for PRC, 5.7 vs. 9.4 and 16.9 vs. 22.7 ng/dl for PAC, P
