Variability of Aldosterone Measurements During Adrenal Venous Sampling for Primary Aldosteronism

Comparative Analysis of Single-Path and Multipath Adrenal Venous Sampling in Primary Aldosteronism

Objective

To evaluate the safety and efficacy of adrenal venous sampling (AVS) via the cubital vein and femoral vein synchronously.

Methods

A total of 200 patients with primary aldosteronism admitted to the First Hospital of Fujian Medical University were enrolled and randomly divided into a single-path AVS group (SP, N = 108) and a multipath AVS group (MP, N = 92). We analyzed the clinical characteristics, intubation success rate, procedure cost, total fluoroscopy time, complications, contrast dosage, and the number of catheters selected during AVS. A planar quadrant system was established to mark the direction of the adrenal opening, with the intersection of the right renal vein and the inferior vena cava defined as the origin. In digital subtraction angiography images, the RAV opening located in the 0-3 o'clock direction was the first quadrant (I), and the 3-6 o'clock direction was the third quadrant (III).

Results

There was no statistical difference between the two groups at baseline. Multipath AVS had a significantly higher success rate of right-sided intubation than single-path AVS (success rate of right-sided intubation/%: SP 87.96 vs MP 95.65, P = 0.043). Total fluoroscopy time was significantly reduced (fluoroscopy time/min: SP 9.80 ± 4.07 vs MP 7.42 ± 3.48, P = 0.024) and the cost of the procedure was markedly lower (cost/yuan: SP 3,900.93 ± 1,191.12 vs MP 3,378.26 ± 399.40, P < 0.001). There was no significant difference in postoperative complications between the two groups. In the group I, the procedure was completed mainly with an MPA catheter (catheter selection/%: MPA 98.19 vs TIG 17.65, P < 0.001). In the group III, TIG catheters were used more frequently (catheter selection/%: MPA 1.81 vs TIG 82.35, P < 0.001).

Conclusion

Multipath AVS via the cubital vein and femoral vein improves the success rate of AVS with comparable safety compared to single-path AVS. When the RAV is opened in the III quadrant, the TIG catheter improves the cannulation success rate. The multipath AVS method provides more catheter options. Patients diagnosed with PA at the First Hospital of Fujian Medical University from December 2019 to December 2021 were included. The collection of medical records of the included population was approved by the ethics committee (approval number: [2021] 311). This was a cross-sectional study in which some patients were treated surgically and some were treated with superselective adrenal artery embolization (SAAE). We conducted a cohort study of patients treated with SAAE. ClinicalTrials.gov Protocol Registration and Results System (PRS) receipt release date: January 11, 2022. This trial is registered with NCT05188872.

Role of Adrenal Vein Sampling in Guiding Surgical Decision in Primary Aldosteronism

Adrenal vein sampling (AVS) is recommended for subtyping primary aldosteronism (PA) to identify lateralized or bilateral sources of aldosterone excess, allowing for better decision-making in regard to medical or surgical management on a case-by-case basis. To date, no consensus exists on protocols to be used during AVS, especially concerning sampling techniques, the timing of sampling, and whether or not to use adrenocorticotropic hormone (ACTH) stimulation. Interpretation criteria for selectivity, lateralization, and contralateral suppression vary from one expert center to another, with some favoring strict cut-offs to others being more permissive. Clinical and biochemical post-operative outcomes can also be influenced by AVS criteria utilized to indicate surgical therapy.In this review, we reanalyze studies on AVS highlighting the recent pathological findings of frequent micronodular hyperplasia adjacent to a dominant aldosteronoma (APA) overlapping with bilateral idiopathic hyperaldosteronism (IHA) etiologies, as opposed to the less frequent unilateral single aldosteronoma. The variable expression of melanocortin type 2 receptors in the nodules and hyperplasia may explain the frequent discordance in lateralization ratios between unstimulated and ACTH- stimulated samples. We conclude that aldosterone values collected during simultaneous bilateral sampling, both at baseline and post-ACTH stimulation, are required to adequately evaluate selectivity, lateralization, and contralateral suppression during AVS, to better identify all patients with PA that can benefit from a surgical indication. Recommended cut-offs for each ratio are also presented.

Impact of Conducting Adrenal Venous Sampling in the Morning Versus Afternoon in Primary Aldosteronism

Context

Adrenal venous sampling (AVS) is the gold standard technique for subtype differentiation of primary aldosteronism (PA) and to obtain aldosterone and cortisol measurements; however, their secretion patterns show fluctuations during the day.

Objective

We aimed to examine the effects of AVS timing on AVS results.

Methods

This multicenter, retrospective, observational study included a total of 753 patients who were diagnosed with PA and underwent AVS in 4 centers in Japan. Among them, 504 and 249 patients underwent AVS in the morning (AM-AVS) and in the afternoon (PM-AVS), respectively. The outcome measures were the impact of AVS timing and hormone fluctuations in a day on AVS results.

Results

There were no differences in the success rate of AVS, diagnostic rate of disease type, or frequency of discrepancy in PA subtypes between the AM-AVS and PM-AVS groups. Regarding patients with unilateral PA, aldosterone concentrations in adrenal venous blood did not differ between the 2 groups on the dominant or nondominant side. Conversely, regarding patients with bilateral PA, aldosterone concentrations in adrenal venous blood were significantly higher in the AM-AVS than in the PM-AVS group.

Conclusions

The timing of AVS did not seem to have a significant impact on subtype diagnosis. The aldosterone levels in adrenal venous blood were significantly higher in patients with bilateral PA in the AM-AVS group, but there was no such difference between patients with unilateral PA in the AM-AVS and PM-AVS groups. Each subtype may have a different hormone secretion pattern in a day.

Aldosterone, Renin, and Aldosterone-to-Renin Ratio Variability in Screening for Primary Aldosteronism

CONTEXT

The plasma aldosterone concentration (PAC), renin, and aldosterone-to-renin ratio (ARR) are used to screen for primary aldosteronism (PA). Substantial intra-individual variability of PAC and ARR using plasma renin activity in the context of usual antihypertensive therapy has been described, but there is no data on ARR variability calculated using direct renin concentration (DRC).

OBJECTIVE

To describe the intra-individual variability of PAC, DRC, and ARR in the absence of interfering medications in patients with and without PA.

DESIGN

Retrospective cohort study.

PATIENTS

Hypertensive patients referred for investigation of PA, with at least 2 ARR measurements while off interfering medications.

SETTING

Endocrine hypertension service of a tertiary center, from May 2017 to July 2021.

MAIN OUTCOME MEASURES

PAC, DRC, and ARR variability was calculated as coefficient of variation (CV) and percent difference (PD).

RESULTS

Analysis of 223 patients (55% female, median age 52 years), including 162 with confirmed PA, demonstrated high variability with a sample CV of 22-25% in the PAC and sample CV of 41% to 42% in the DRC and ARR in both the PA and non-PA groups. The degree of variability was substantially higher than the assays' analytical CV. Sixty-two patients (38%) with PA had at least one ARR below 70 pmol/L:mU/L (2.4 ng/dL:mU/L), a cut-off for first-line screening of PA.

CONCLUSIONS

Significant intra-individual variability in PAC, DRC, and hence ARR occurs in a large proportion of patients being investigated for PA. These findings support the need for at least 2 ARR before PA is excluded or further investigated.

Primary Aldosteronism: State-of-the-Art Review

We are witnessing a revolution in our understanding of primary aldosteronism (PA). In the past 2 decades, we have learned that PA is a highly prevalent syndrome that is largely attributable to pathogenic somatic mutations, that contributes to cardiovascular, metabolic, and kidney disease, and that when recognized, can be adequately treated with widely available mineralocorticoid receptor antagonists and/or surgical adrenalectomy. Unfortunately, PA is rarely diagnosed, or adequately treated, mainly because of a lack of awareness and education. Most clinicians still possess an outdated understanding of PA; from primary care physicians to hypertension specialists, there is an urgent need to redefine and reintroduce PA to clinicians with a modern and practical approach. In this state-of-the-art review, we provide readers with the most updated knowledge on the pathogenesis, prevalence, diagnosis, and treatment of PA. In particular, we underscore the public health importance of promptly recognizing and treating PA and provide pragmatic solutions to modify clinical practices to achieve this.

Intraindividual variability of serum aldosterone and its implication for primary aldosteronism screening

CONTEXT

Primary aldosteronism (PA) screening relies on an elevated aldosterone to renin ratio with a minimum aldosterone level, which varies from 10 to 15 ng/dL (277 to 415.5 pmol/L) using immunoassay.

AIM

To evaluate intraindividual coefficient of variation (CV) of aldosterone and aldosterone to direct renin concentration ratio (A/DRC) and its impact on PA screening.

METHODS

A total of 671 aldosterone and DRC measurements were performed by the same chemiluminescence assays in a large cohort of 216 patients with confirmed PA and at least two screenings.

RESULTS

The median intraindividual CV of aldosterone and A/DRC was 26.8% and 26.7%. Almost 40% of the patients had at least one aldosterone level <15 ng/dL, 19.9% had at least two aldosterone levels <15 ng/dL and 16.2% had mean aldosterone levels <15 ng/dL. A lower cut-off of 10 ng/dL was associated with false negative rates for PA screening of 14.3% for a single aldosterone measurement, 4.6% for two aldosterone measurements and only 2.3% for mean aldosterone levels. Considering the minimum aldosterone, true positive rate of aldosterone thresholds was 85.7% for 10 ng/dL and 61.6% for 15 ng/dL. An A/DRC >2 ng/dL/µIU/mL had a true positive rate for PA diagnosis of 94.4% and 98.4% when based on one or two assessments, respectively. CV of aldosterone and A/DRC were not affected by sex, use of interfering anti-hypertensive medications, PA lateralization, hypokalemia, age and number of hormone measurements.

CONCLUSION

Aldosterone concentrations had a high CV in PA patients, which results in an elevated rate of false negative test in a single screening for PA. Therefore, PA screening should be based in at least two screenings with concomitant aldosterone and renin measurements.

The Entity of Connshing Syndrome: Primary Aldosteronism with Autonomous Cortisol Secretion

Connshing syndrome (CoSh) (adrenal-related synchronous aldosterone (A) and cortisol (C) excess) represents a distinct entity among PA (primary hyperaldosteronisms) named by W. Arlt et al. in 2017, but the condition has been studied for more than 4 decades. Within the last few years, this is one of the most dynamic topics in hormonally active adrenal lesions due to massive advances in steroids metabolomics, molecular genetics from CYP11B1/B2 immunostaining to genes constellations, as well as newly designated pathological categories according to the 2022 WHO classification. In gross, PA causes 4-10% of all high blood pressure (HBP) cases, and 20% of resistant HBP; subclinical Cushing syndrome (SCS) is identified in one-third of adrenal incidentalomas (AI), while CoSh accounts for 20-30% to 77% of PA subjects, depending on the tests used to confirm autonomous C secretion (ACS). The clinical picture overlaps with PA, hypercortisolemia being mild. ACS is suspected in PA if a more severe glucose and cardiovascular profile is identified, or there are larger tumours, ACS being an independent factor risk for kidney damage, and probably also for depression/anxiety and osteoporotic fractures. It seems that one-third of the PA-ACS group harbours mutations of C-related lines like PRKACA and GNAS. A novel approach means we should perform CYP11B2/CYP11B1 immunostaining; sometimes negative aldosteronoma for CYP11B1 is surrounded by micronodules or cell clusters with positive CYP11B1 to sustain the C excess. Pitfalls of hormonal assessments in CoSh include the index of suspicion (check for ACS in PA patients) and the interpretation of A/C ratio during adrenal venous sample. Laparoscopic adrenalectomy is the treatment of choice. Post-operative clinical remission rate is lower in CoSh than PA. The risk of clinically manifested adrenal insufficiency is low, but a synthetic ACTH stimulating testing might help to avoid unnecessary exposure to glucocorticoids therapy. Finally, postponing the choice of surgery may impair the outcome, having noted that long-term therapy with mineralocorticoids receptors antagonists might not act against excessive amounts of C. Awareness of CoSh improves management and overall prognosis.

Performance of Confirmatory Tests for Diagnosing Primary Aldosteronism: a Systematic Review and Meta-Analysis

Background:

Confirmatory tests are recommended for diagnosing primary aldosteronism, but the supporting evidence is unclear.

Methods:

We searched Medline, EMBASE, and the Cochrane Central Register of Controlled Trials. Studies evaluating any guideline-recommended confirmatory test (ie, saline infusion test, salt loading test, fludrocortisone suppression test, and captopril challenge test), compared with a reference standard were included. The Quality Assessment of Diagnostic Accuracy Studies-2 tool was used to assess the risk of bias. Meta-analyses were conducted using hierarchical summary receiver operating characteristic models.

Results:

Fifty-five studies were included, comprising 26 studies (3654 participants) for the recumbent saline infusion test, 4 studies (633 participants) for the seated saline infusion test, 2 studies (99 participants) for the salt loading test, 7 studies (386 participants) for the fludrocortisone suppression test, and 25 studies (2585 participants) for the captopril challenge test. Risk of bias was high, affecting more than half of studies, and across all domains. Studies with case-control sampling overestimated accuracy by 7-fold (relative diagnostic odds ratio, 7.26 [95% CI, 2.46–21.43]) and partial verification or use of inconsistent reference standards overestimated accuracy by 5-fold (5.12 [95% CI, 1.48–17.77]). There were large variations in how confirmatory tests were conducted, interpreted, and verified. Under most scenarios, confirmatory testing resulted in an excess of missed cases. The certainty of evidence underlying each test (Grading of Recommendations, Assessment, Development, and Evaluations) was very low.

Conclusions:

Recommendations for confirmatory testing in patients with abnormal screening tests and high probability features of primary aldosteronism are based on very low-quality evidence and their routine use should be reconsidered.

Successful Adrenal Vein Sampling Using Dexamethasone Premedication in Patients With Iodine Contrast Media Allergy

Context

Preparation of patients with iodine contrast media (ICM) allergy who require adrenal vein sampling (AVS) to establish source of aldosterone excess of their confirmed primary aldosteronism (PA) is controversial. Usual premedication with high-dose prednisone can interfere with cortisol determinations, possibly altering the aldosterone to cortisol ratios for the identification of lateralized aldosterone excess.

Objective

We aimed to evaluate the efficacy and safety of premedication with high-dose dexamethasone to perform AVS in patients with ICM.

Methods

One hundred and seventy-seven consecutive patients with confirmed PA who underwent bilateral simultaneous basal and post-ACTH bolus AVS at our center between January 2010 and December 2020 were retrospectively analyzed for history of ICM allergy. A total of 7 patients (4%) with previous allergic reactions to ICM were prepared with 3 doses of 7.5 mg dexamethasone premedication rather than the usual 50 mg of prednisone.

Results

No breakthrough allergic reactions were reported in the 7 patients. Despite adequate serum cortisol suppression following dexamethasone, the basal and post-ACTH selectivity index were respectively &gt; 2 and &gt; 5 bilaterally in all patients, confirming adequate cannulation of both adrenal veins. Four patients had lateralized ratios (A/C ratio &gt; 2 basally and &gt; 4 post-ACTH), while 3 had bilateral source during AVS study. In the 3 patients undergoing unilateral adrenalectomy for lateralized source and contralateral suppression and adequate follow-up data, cure of PA was achieved at mean 58 months postoperatively.

Conclusion

AVS using dexamethasone premedication is safe and accurate for diagnosing the source of aldosterone excess in patients with PA and ICM allergy.

Re-Calibrating Interpretations of Aldosterone Assays Across the Physiologic Range: Immunoassay and Liquid Chromatography-Tandem Mass Spectrometry Measurements Under Multiple Controlled Conditions

Context

Clinicians frequently rely on aldosterone thresholds derived from older immunoassays to diagnose primary aldosteronism. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is increasingly widespread and reported to yield lower aldosterone concentrations.

Objective

Given the health impact of incorrect interpretations of aldosterone levels, we compared measurements using LC-MS/MS and immunoassay across the full range of aldosterone physiology by evaluating distinct regulation by angiotensin II and adrenocorticotropin (ACTH).

Methods

Normotensive volunteers underwent prospective characterization of aldosterone production by immunoassay and LC-MS/MS during 4 conditions (n = 188): oral sodium suppression and restriction (to assess angiotensin II–mediated aldosterone production) and dexamethasone suppression and cosyntropin stimulation (to assess ACTH-mediated aldosterone production).

Results

Serum aldosterone concentrations by LC-MS/MS and immunoassay had a correlation of 0.69 (P < .001), with good agreement (intraclass correlation 0.76; 95% CI 0.52-0.87). Aldosterone was lower by LC-MS/MS than immunoassay (median 10.5 [3.8, 21.9] vs 19.6 [9.5, 28.0] ng/dL; P < .001), with an average difference of 37.2%. The most notable discrepancy was in the clinically discriminatory range <20 ng/dL: 9.9 (7.1, 13.8) ng/dL using immunoassay corresponded to 5.5 (1.4, 8.9) ng/dL by LC-MS/MS (P < .001). Following oral sodium suppression, the aldosterone-to-renin ratio was 4-fold higher using immunoassay (27.2 [19.7, 62.4] vs 6.4 [3.5, 19.1] ng/dL per ng/mL/hour; P < .001).

Conclusion

Aldosterone measurements are substantially lower by LC-MS/MS than immunoassay across the full physiologic range, especially when aldosterone levels were less than 20 ng/dL. These findings highlight the need to recalibrate diagnostic interpretations when measuring aldosterone via LC-MS/MS and provide insights into potential biologic causes of assay differences.

Morphologically Normal-Appearing Adrenal Glands as a Prevalent Source of Aldosterone Production in Primary Aldosteronism

BACKGROUND

Normal-appearing adrenal glands on cross-sectional imaging may still be the source of aldosterone production in primary aldosteronism (PA).

METHODS

We evaluated the prevalence of aldosterone production among morphologically normal-appearing adrenal glands and the impact of this phenomenon on interpretations of localization studies and treatment decisions. We performed a retrospective cohort study of PA patients with at least 1 normal adrenal gland and reanalyzed contemporary studies to assess interpretations of imaging and adrenal venous sampling (AVS) at the individual patient and adrenal levels.

RESULTS

Among 243 patients, 43 (18%) had bilateral normal-appearing adrenals and 200 (82%) had a unilateral normal-appearing adrenal, for a total of 286 normal-appearing adrenal glands. 38% of these normal-appearing adrenal glands were a source of aldosteronism on AVS, resulting in discordance between imaging and AVS findings in 31% of patients. Most patients with lateralizing PA underwent curative unilateral treatment (80%); however, curative treatment was pursued in 92% of patients who had concordant imaging-AVS results but in only 38% who had discordant results (P < 0.05). In young patients, imaging-AVS discordance was detected in 32% of those under 45 years and 21% of those under 35 years. Among 20 contemporary studies (including 4,904 patients and 6,934 normal-appearing adrenal glands), up to 64% of normal-appearing adrenals were a source of aldosteronism resulting in 31% of patients having discordant results.

CONCLUSIONS

Morphologically normal-appearing adrenal glands are commonly the source of aldosterone production in PA, even among young patients. The lack of awareness of this issue may result in inappropriate treatment recommendations.

Anatomical Variations of the Left Adrenal Vein Encountered During Venous Sampling

PURPOSE

To identify anatomical variations in the left adrenal vein (LAV) and to evaluate the role of preprocedural contrast-enhanced computed tomography (CT) planning.

METHODS

The length of the left adrenal central vein (LACV), the vessel that receives blood from all tributaries of the left adrenal gland, was measured using venograms of patients who had undergone adrenal venous sampling (AVS) for the diagnosis of primary aldosteronism between October 2017 and December 2019. The anatomical variants of the LAV were described and classified. Contrast-enhanced CT was used to evaluate the detection rate of the following: (a) confluence of the left inferior phrenic vein and the LAV and (b) the last tributary flowing into the LAV.

RESULTS

In total, 311 patients (143 men, 168 women; mean age: 49.3 years ± 11.0) were enrolled. Of them, 9 (2.9%) patients had anatomical variants lacking a LACV. In patients with a LACV (n = 302), the venographic LACV length was 9.0 mm ± 3.9 (<1 mm in 9 patients). The detection rate of the confluence of the left inferior phrenic vein and LAV, as determined using contrast-enhanced CT, was high (96.2%), whereas that of the last tributary flowing into the LAV was low (0.8%). In 4 of 18 patients with short or absent LACV, the variant was visualized using contrast-enhanced CT.

CONCLUSIONS

In some patients, the LACV is absent or short, which is an anatomical variation. Understanding venographic anatomical variations can help avoid misleading results resulting from a suboptimal sampling site in AVS. For some subtypes, contrast-enhanced CT may also help in planning the AVS procedure.

Adrenocorticotropic Hormone-Stimulated Adrenal Venous Sampling Underestimates Surgically Curable Primary Aldosteronism: A Retrospective Cohort Study and Review of Contemporary Studies

[Figure: see text].

Primary aldosteronism

In 1955 Dr Jerome Conn first documented primary aldosteronism (PA). Since then, screening, diagnosis and treatment have developed, in the process both refining and complicating management. Currently, screening requires 4-6 weeks of lead-up, including major changes in antihypertensive therapy, followed by a blood draw for plasma aldosterone concentration (PAC) and plasma renin activity (PRA) or concentration (PRC). Screening is considered indicative of PA on the basis of the PAC and the aldosterone to renin ratio (ARR). This is then followed by one or more of 6 confirmatory/exclusion tests. Three things have changed. First is now incontrovertible evidence that a single spot PAC is a deeply flawed index of true aldosterone status, so that many referred patients with PA fall at the first hurdle. A valid index of aldosterone status is an integrated value, measured as urinary aldosterone excretion (UEA) over 24 h. On the basis of the UEA, the prevalence of PA appears to be 3-5 times higher than the currently accepted figure of 5-10% of hypertensives. The second is the recognition that inadequately treated PA has a cardiovascular risk profile ~threefold that of matched essential hypertensives. Third is the realization that <1% of hypertensives are ever screened for PA, who are thus in double jeopardy for the risks of untreated PA on top of those for hypertension per se. Taken together, this a major if occult public health issue; if it is to be addressed, radical changes in management are needed. Some are in screening, which needs to be simply done on all newly-presenting hypertensives; others are major simplifications of screening in established hypertension. The front-line actors need to be Internists/Primary Care Providers; the costs will be significant, but much less than those of increased morbidity/premature mortality in unrecognized PA. Possible suggestions as to how best to address this constitute the final chapter of this article.

Repeat Adrenal Vein Sampling in Aldosteronism: Reproducibility and Interpretation of Persistently Discordant Results

CONTEXT

The reproducibility of adrenal vein sampling (AVS) is unknown.

OBJECTIVE

This work aimed to determine reproducibility of biochemical results and diagnostic lateralization in patients undergoing repeat AVS.

METHODS

A retrospective chart review was conducted of single-center, single-operator AVS procedures at a tertiary care center. Included were patients with confirmed primary aldosteronism (PA) undergoing repeat AVS because of concerns about technical success or discordant diagnostic results. Simultaneous AVS was performed by an experienced operator using a consistent protocol of precosyntropin and postcosyntropin infusion. Among successfully catheterized adrenal veins (selectivity index ≥ 2), the correlation of the adrenalaldosterone/cortisol (A/C) ratio was measured between the first and second AVS. The secondary outcome measure was diagnostic agreement on repeat AVS lateralization (lateralization index ≥ 3).

RESULTS

There were 46 sets of AVS from 23 patients at a median of 3 months apart. There was moderate correlation in A/C ratios in the adrenal veins and inferior vena cava (Spearman r = 0.49-0.59, P < .05) pre cosyntropin. Post cosyntropin, the correlation was better (Spearman r = 0.67-0.76, P < .05). In technically successful AVS, there was moderate correlation between the repeated lateralization indices (Spearman r = 0.53, P < .05). In 15 patients in whom repeat AVS was performed because of apparent lateralization discordance with computed tomography imaging, the final diagnosis was the same in the second AVS procedure. Initial failed AVS was successful 75% of the time on repeat attempt.

CONCLUSION

Repeat AVS was feasible and usually successful when an initial attempt failed. There was modest correlation between individual repeat adrenal A/C ratios and lateralization indices when AVS was performed twice. The final lateralization diagnosis was identical in all cases. This demonstrates that AVS is a reliable and reproducible localizing test in PA.

Intraindividual Variability of Aldosterone Concentrations in Primary Aldosteronism: Implications for Case Detection

Primary aldosteronism is an underdiagnosed cause of hypertension. Although inadequate screening is one reason for underdiagnosis, another important contributor is that clinicians may inappropriately exclude the diagnosis when screening aldosterone concentrations fall below traditionally established thresholds. We evaluated the intraindividual variability in screening aldosterone concentrations and aldosterone-to-renin ratios, and how this variability could impact case detection, among 51 patients with confirmed primary aldosteronism who had 2 or more screening measurements of renin and aldosterone on different days. There were a total of 137 screening measurements with a mean of 3 (range 2-6) per patient. The mean intraindividual variability, expressed as coefficients of variation, was 31% for aldosterone and 45% for the aldosterone-to-renin ratio. Aldosterone concentrations ranged from 4.9 to 51 ng/dL; 49% of patients had at least one aldosterone measurement below 15 ng/dL, 29% had at least 2 aldosterone measurements below 15 ng/dL, and 29% had at least one measurement below 10 ng/dL. Individual aldosterone-to-renin ratios ranged from 8.2 to 427 ng/dL per ng/mL·hour; 57% had at least one ratio below 30 ng/dL per ng/mL·hour, 27% had at least 2 ratios below 30 ng/dL per ng/mL·hour, and 24% had at least one ratio below 20 ng/dL per ng/mL·hour. Aldosterone concentrations and aldosterone-to-renin ratios are highly variable in patients with primary aldosteronism, with many screening values falling below conventionally accepted diagnostic thresholds. The diagnostic yield for primary aldosteronism may be substantially increased by recalibrating the definition of a positive screen to include more liberal thresholds for aldosterone and the aldosterone-to-renin ratio.