Comparison of three different chemiluminescence assays and a rapid liquid chromatography tandem mass spectrometry method for measuring serum aldosterone

Comparing ARR Versus Suppressed PRA as Screening Tests for Primary Aldosteronism

BACKGROUND

In many practices, the screening for primary aldosteronism relies on a single-blood draw for plasma aldosterone concentration (PAC) and plasma renin activity (PRA) to establish an aldosterone-to-renin ratio (ARR). ARR levels vary between expert centers and repeated assays in the same individual, emphasizing the potential variability of this screening approach. A suppressed PRA to <1 ng/mL per h has been proposed as an alternative test to the ARR.

METHODS

We compared 2 potential screening approaches to identify probable primary aldosteronism (ARR≥30 or ARR≥20 versus PRA suppressed below 1 ng/mL per h) in a cohort of 94 829 paired PRA and PAC samples submitted by clinicians to evaluate the presence of primary aldosteronism.

RESULTS

Of 94 829 patients, 20.3% tested positive based on ARR≥20 (95% CI, 20.0%-20.5%), 13.9% based on ARR≥30 (95% CI, 13.6%-14.1%), versus 45.9% based on suppressed PRA (<1 ng/mL per minute [95% CI, 45.5%-46.2%]). In the PRA group, a range of aldosterone levels was observed: 5.5% had PAC >15 ng/dL, 25.2% had PAC 5 to 15 ng/dL, and 15.2% had PAC <5 ng/dL, compared with 6%, 12.7%, and 1.6% in the ARR≥20 group and 4.7%, 8.5%, and 0.7% in the ARR≥30 group.

CONCLUSIONS

In this cohort of individuals being screened for primary aldosteronism, substantially more individuals were identified using criteria focused on suppression of renin activity compared with using the aldosterone renin ratio as a screening tool.

Liquid chromatography-tandem mass spectrometry in clinical laboratory protein measurement

Proteins are essential components of human cells and tissues, and they are commonly measured in clinical laboratories using immunoassays. However, these assays have certain limitations, such as non-specificity binding, insufficient selectivity, and interference of antibodies. More sensitive, accurate, and efficient technology is required to overcome these limitations. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful analytical tool that provides high sensitivity and specificity, making it superior to traditional methods such as biochemical methods and immunoassays. While LC-MS/MS has been increasingly used for detecting small molecular analytes and steroid hormones in clinical practice recently, its application for protein or peptide analysis is still in its early stages. Established methods for quantifying proteins and peptides by LC-MS/MS are mainly focused on scientific research, and only a few proteins and peptides can be or have the potential to be detected and applied in clinical practice. Therefore, this article aims to review the clinical applications, advantages, and challenges of analyzing proteins and peptides using LC-MS/MS in clinical laboratories.

Effects of sodium intake, age, gender, blood sampling time on distribution of plasma aldosterone, renin activity, deoxycorticosterone, cortisol, cortisone, and 24 h urinary aldosterone levels in normotensive individuals based on LC-MS/MS

PURPOSE

This study aims to analyze the distribution of plasma aldosterone, renin activity, deoxycorticosterone (DOC), cortisol, cortisone, and 24 h urinary aldosterone (24 h-uAld) levels based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

MATERIALS AND METHODS

Plasma and 24 h urine were collected from 129 healthy volunteers in Northeast China. The effect of sodium intake, age, gender, blood sampling time on plasma aldosterone concentration (PAC), plasma renin activity (PRA), PAC to PRA ratio (ARR), DOC, cortisol, cortisone, cortisol to cortisone ratio, and 24 h-uAld were investigated by nonparametric test, multiple linear regression and Harris-Boyd's standard deviate test.

RESULTS

There was no significant difference observed in 24 h-uAld, PAC (AM), PRA(AM), ARR (AM), DOC (AM), cortisol (AM), cortisone (AM), and cortisol to cortisone (AM) between high and low sodium intake group. Significant differences were observed between morning and afternoon sampling groups in terms of PAC, ARR, DOC, cortisol, and cortisone. Reference intervals (RIs) of 24 h-uAld, PAC (AM) were recommended to be partitioned by gender. RI of PRA was recommended age stratification.

CONCLUSION

We recommend that the same reference interval could be used regardless of sodium intake. Gender is the main influence factor for 24 h-uAld, PAC, and ARR. Age is key influence factor for PRA.

Laboratory Testing for Endocrine Hypertension: Current and Future Perspectives

BACKGROUND

Secondary hypertension (SH) is a form of high blood pressure caused by an identifiable underlying condition. Although, it accounts for a small fraction of the overall hypertensive population, detection and management of SH is of utmost importance, because SH phenotypes carry a high cardiovascular risk and can possibly be cured by timely treatment.

CONTENT

This review focuses on the endocrine causes of SH, such as primary aldosteronism, Cushing syndrome, thyroid disease, pheochromocytoma and paraganglioma, acromegaly, and rare monogenic forms. It discusses current biomarkers, analytical methods, and diagnostic strategies, highlighting advantages and limitations of each approach. It also explores the emerging -omics technologies that can provide a comprehensive and multidimensional assessment of SH and its underlying mechanisms.

SUMMARY

Endocrine SH is a heterogeneous and complex condition that requires proper screening and confirmatory tests to avoid diagnostic delays and improve patient outcomes. Careful biomarker interpretation is essential due to potential interferences, variability, and method-dependent differences. Liquid chromatography-tandem mass spectrometry is a superior method for measuring low-concentration hormones and metabolites involved in SH, but it requires expertise. Omics approaches have great potential to identify novel biomarkers, pathways, and targets for SH diagnosis and treatment, especially considering its multifactorial nature.

Comparison of plasma aldosterone measured by chemiluminescence immunoassay and liquid chromatography-tandem mass spectrometry in screening test for primary aldosteronism

Background

Whether chemiluminescence immunoassay (CLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for plasma aldosterone concentration (PAC) measurement can be used interchangeably in primary aldosteronism (PA) screening is still controversial. The purpose of this study was to compare CLIA to LC-MS/MS for PAC measurement in PA screening.

Methods

All participants underwent aldosterone-to-renin ratio (ARR) testing. PA was diagnosed by captopril challenge test or saline infusion test. PAC in screening test was measured with CLIA and LC-MS/MS. Plasma direct renin concentration in screening and confirmatory test was measured with CLIA. The concordance between CLIA and LC-MS/MS for PAC measurement in PA screening was analyzed.

Results

Twenty-one healthy volunteers, 61 patients with essential hypertension (EH) and 43 PA patients were enrolled. Median PAC by CLIA was 84.7 % higher than that by LC-MS/MS in screening test (P < 0.001). A positive correlation of PAC was observed between the two assays (Pearson r coefficient 0.770, P < 0.001). When ARR was used in differentiating PA from EH, there was no difference in the area under the receiver operating characteristic curve between CLIA and LC-MS/MS for PAC measurement (0.968 vs 0.950, P = 0.249).

Conclusion

CLIA and LC-MS/MS for PAC measurement exhibited high and comparable efficacy in PA screening. CLIA is a reliable and feasible alternative in PA screening test.

A case report of a young boy with low renin and high aldosterone levels induced by Liddle syndrome who was previously misdiagnosed with primary aldosteronism

OBJECTIVES

Liddle syndrome is an autosomal dominant hereditary disease caused by a single gene mutation. Typical clinical manifestations are early-onset hypertension and hypokalemia.

CASE PRESENTATION

This report describes a 17-year-old male with hypertension and hypokalemia. We performed Captopril inhibition and postural stimulation test to diagnose and type primary aldosteronism. The plasma renin activity was consistently low, and aldosterone levels were high, hence the patient was initially diagnosed with primary aldosteronism. After genetic analysis, a diagnosis of Liddle syndrome was made due to the presence of a p. Pro617Ser mutation in the SCNN1B gene. After diagnosis, the patient was prescribed one tablet of amiloride twice a day. The patient's blood pressure (average in 120-135/70-80 mmHg) and serum potassium levels (3.6-4.0 mmol/L) returned to normal and was well-controlled after treatment.

CONCLUSIONS

Adolescent hypertension may be secondary to underlying medical conditions affecting the heart, kidneys, or endocrine system or primary with no known underlying disease process. Although in an adolescent with hypertension, hyperaldosteronism, and low plasma renin activity, the initial diagnosis suggested primary hyperaldosteronism, the failure of aldosterone receptor antagonist's therapy led to the diagnosis of Liddle syndrome. Increased aldosterone levels should always be evaluated with caution before a definitive diagnosis to prevent misdiagnosis. Genetic testing is the gold standard for the diagnosis of Liddle syndrome. Early diagnosis and early precise treatment can restore normal blood pressure and prevent severe sequelae of chronic hypertension in patients.

Liddle syndrome misdiagnosed as primary aldosteronism is caused by inaccurate aldosterone-rennin detection while a novel SCNN1G mutation is discovered

PURPOSE

Through describing the confusing misdiagnosis process of Liddle syndrome, we try to reveal the importance of accurate aldosterone-renin detection and a genetic test for Liddle syndrome.

METHODS

We found a family of hypertension and hypokalaemia with the proband of a 21-year-old female who had been misdiagnosed as primary aldosteronism (PA). She presented with high aldosterone and low renin levels. Aldosterone is not suppressed in the saline infusion test and captopril challenge test. However, treatment with a standard dose of spironolactone has no blood pressure improvement effect. A heterozygous variant of SCNN1G was found with whole exome sequencing and Liddle syndrome is indicated. Treatment with amiloride was effective. We rechecked aldosterone-renin levels with two different aldosterone and renin test kits. Clinical features and the mutant gene SCNN1G of each family member were determined by the Sanger method.

RESULTS

The two kits had nearly opposite results. Among those Liddle syndrome patients confirmed by a genetic test, for Test kit A all ARR were screened positive while for test kit B negative. It seems Test kit B is consistent with the diagnosis while test kit A misleads the diagnosis. A novel SCNN1G mutation, c.1729 C > T, was found in this family, which introduce a premature stop codon in the γ subunit in the epithelial Na⁺ channel (ENaC) and resulted in a deletion of 72 amino acids at the carboxyl end.

CONCLUSION

inaccurate ARR detection might misdiagnose Liddle syndrome. A Gene test is an important method for the diagnosis of Liddle syndrome. A novel SCNN1G missense mutation, c.1729 C > T, is found in a Chinese family.

Recalibrating 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.

Performance of the aldosterone-to-renin ratio as a screening test for primary aldosteronism in primary care

Primary aldosteronism (PA) is the most common and potentially curable form of secondary hypertension, affecting 5-10% of primary care patients with hypertension. Primary care physicians have an important role in initiating the screening for PA in patients with hypertension and referring to a specialist service depending on the screening test results. The currently recommended screening test for PA is the plasma aldosterone-to-renin ratio (ARR). Test results are influenced by medications so careful patient preparation is required including adjusting existing antihypertensive medications to avoid diagnostic errors. A range of laboratory method-dependent ARR thresholds are used for the screening of PA around the world. Periodic clinical audits and case reviews by clinicians and the laboratory may help refine the local thresholds. Patients with an abnormally elevated ARR should be referred to a specialist for confirmatory testing while patients with a high pre-test probability but a normal ARR could have a repeat test in view of the within-individual variability. Despite the heterogenous ARR thresholds, measuring the ARR is still more likely to detect PA than not screening at all.

Preoperative mineralocorticoid receptor antagonist reduces postoperative hyperkalaemia in patients with Conn syndrome

BACKGROUND

The preoperative use of mineralocorticoid receptor antagonists (MRA) in patients with unilateral forms of primary aldosteronism (PA) is not standardized. The current Endocrine Society Guidelines do not specifically recommend MRA treatment before surgery. It is unclear whether preoperative MRA can optimize perioperative blood pressure and potassium control, and reduce the incidence of postoperative hyperkalaemia.

OBJECTIVE

This study aimed to investigate the effect of MRA on the incidence of postoperative hyperkalaemia in addition to perioperative blood pressure and potassium concentration in patients undergoing unilateral adrenalectomy for the treatment of PA.

DESIGN

Retrospective cohort study.

SETTING

Tertiary referral centres, Victoria, Australia.

PATIENTS

A total of 96 patients who were diagnosed with unilateral forms of PA: 73 patients ('MRA' group) received preoperative MRA while 23 patients ('No-MRA' group) did not.

RESULTS

The prevalence of postoperative hyperkalaemia was significantly higher in the 'No-MRA' group at 2-4 weeks after surgery, compared to the 'MRA' group (35% vs. 11%, p = .014). In a logistic regression, the use of MRA significantly predicted a lower incidence of postoperative hyperkalaemia after adjusting for age, sex, baseline aldosterone-to-renin ratio, potassium and preoperative eGFR. Before surgery, patients in the 'MRA' group had normalized blood pressure and potassium concentration requiring fewer antihypertensive medications and no potassium supplements.

CONCLUSION

Preoperative MRA use was associated with optimal perioperative blood pressure and normalized serum potassium in addition to a lower incidence of postoperative hyperkalaemia. MRA should be considered standard treatment for patients awaiting surgery for PA.

Clinical diagnostic value of liquid chromatography-tandem mass spectrometry method for primary aldosteronism in patients with hypertension: A systematic review and meta-analysis

BACKGROUND

Primary aldosteronism (PA) is currently considered the most common cause of secondary and endocrine hypertension. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) as a new detection technique has been gradually applied in the diagnosis of PA. However, the diagnostic value of LC-MS/MS methods for PA has not been systematically clinically validated. The aim was to access the diagnostic accuracy, sensitivity, and specificity of LC-MS/MS methods as screening tools in PA.

MATERIALS AND METHODS

A literature search of PubMed, Embase, Medline, Web of Science, Scopus, Science Direct, and Chinese databases was carried out to June 2022 with no language restriction. Data on sensitivity and specificity and other evaluation indicators were extracted and pooled with STATA and Meta-disc software. Heterogeneity was evaluated and meta-regression and subgroup analysis was performed to elucidate sources of heterogeneity.

RESULTS

12 studies of the diagnostic test were suitable and included in the meta-analysis. Pooled sensitivity, specificity, and diagnostic odds ratio were 0.89 (95% CI: 0.83-0.93), 0.87 (95% CI: 0.82-0.91), and 55 (95% CI: 28-110), respectively. Subgroup analysis assessed the diagnostic power of LC-MS/MS based on the type of detection index. ARR and PAC based on LC-MS/MS methods have the higher diagnostic value compared with other indices, diagnostic odds ratios were 121.65 (95% CI: 36.28-407.98) and 49.85 (95% CI: 24.87-99.93). There was considerable heterogeneity among studies.

CONCLUSION

LC-MS/MS methods had higher accuracy and reliability in the diagnosis of primary aldosteronism. LC-MS/MS-based ARR and PAC can be further promoted and applied in the diagnosis of primary aldosteronism.

Confirmatory testing of primary aldosteronism with saline infusion test and LC-MS/MS

OBJECTIVE

Saline infusion testing (SIT) for confirmation of primary aldosteronism (PA) is based on impaired aldosterone suppression in PA compared to essential hypertension (EH). In the past, aldosterone was quantified using immunoassays (IA). Liquid chromatography tandem mass spectrometry (LC-MS/MS) is increasingly used in clinical routine. We aimed at a method-specific aldosterone threshold for the diagnosis of PA during SIT and explored the diagnostic utility of steroid panel analysis.

DESIGN

Retrospective cohort study of 187 paired SIT samples (2009-2018). Diagnosis of PA (n = 103) and EH (n = 84) was established based on clinical routine workup without using LC-MS/MS values.

SETTING

Tertiary care center.

METHODS

LC-MS/MS using a commercial steroid panel. Receiver operator characteristics analysis was used to determine method-specific cut-offs using a positive predictive value (PPV) of 90% as criterion.

RESULTS

Aldosterone measured by IA was on average 31 ng/L higher than with LC-MS/MS. The cut-offs for PA confirmation were 54 ng/L for IA (sensitivity: 95%, 95% CI: 89.0-98.4; specificity: 87%, 95% CI: 77.8-93.3; area under the curve (AUC): 0.955, 95% CI: 0.924-0.986; PPV: 90%, 95% CI: 83.7-93.9) and 69 ng/L for LC-MS/MS (79%, 95% CI: 69.5-86.1; 89%, 95% CI: 80.6-95.0; 0.902, 95% CI: 0.857-0.947; 90%, 95% CI: 82.8-94.4). Other steroids did not improve SIT.

CONCLUSIONS

Aldosterone quantification with LC-MS/MS and IA yields comparable SIT-cut-offs. Lower AUC for LC-MS/MS is likely due to the spectrum of disease in PA and previous decision making based on IA results. Until data of a prospective trial with clinical endpoints are available, the suggested cut-off can be used in clinical routine.