Fully automated chemiluminescence vs RIA aldosterone assay in primary aldosteronism work-up

Area of Science:

• Endocrinology
• Clinical Chemistry
• Diagnostic Assays

Background:

• Accurate measurement of aldosterone and renin is crucial for diagnosing primary aldosteronism (PA).
• Existing assays have varying thresholds, complicating diagnosis.
• A new fully automated chemiluminescence (CL) immunoassay offers potential for PA screening.

Purpose of the Study:

• To evaluate the accuracy of the CL immunoassay for PA screening and confirmatory testing.
• To compare CL assay results with radioimmunoassay (RIA) for aldosterone and aldosterone to renin ratio (ARR).
• To assess the CL assay's performance in the intravenous saline loading test (ivSLT).

Main Methods:

• Compared aldosterone and ARR measurements using CL and RIA assays.
• Analyzed data from 102 hypertensive patients at baseline and 85 after ivSLT.
• Used Deming regression to assess agreement between the two methods.

Main Results:

• Excellent correlation between CL and RIA for aldosterone (r=0.922) and ARR (r=0.977) overall.
• Established an equivalent ARR cut-off of 20 pg·ml⁻¹·mU⁻¹·l⁻¹ for the CL assay.
• Weaker correlation for low aldosterone concentrations (r=0.676) and lower concordance (68%) in ivSLT results.

Conclusions:

• The CL immunoassay demonstrates comparable performance to RIA for ARR-based PA screening.
• The CL assay is significantly less accurate than RIA for confirmatory ivSLT in diagnosing autonomous aldosterone secretion.
• Further validation is needed for the CL assay in confirmatory diagnostic settings.