PS-BPB04-9: DEVELOPMENT AND VALIDATION OF NEW METHOD TO MEASURE PLASMA ALDOSTERONE AND RENIN ACTIVITY USING LIQUID CHROMATOGRAPHY TANDEM MASS SPECTROMETER (LC-MS/MS)

Abstract

Objective: Measurement of aldosterone, renin, and aldosterone-renin ratio (ARR), are used to diagnose primary aldosteronism (PA). Immunoassays used to measure plasma aldosterone yield higher results compared to tandem mass spectrometry (LC-MS/MS). This can lead to false positive diagnosis of PA, and potential for unnecessary adrenal vein sampling. We report our development and validation of a novel test using LC-MS/MS, with reduced run time, for measurement of plasma aldosterone concentration (PAC) and plasma renin activity (PRA). Design and method: The detection and quantification of plasma aldosterone and angiotensin 1 (product for the calculation of renin activity) in the mass spectrometer was based on the multiple reaction monitoring of precursor to fragment ions under negative and positive ionization modes, respectively. Validation of the tests were based on the CLSI (Clinical & Laboratory Standards Institute) guidelines. Concurrent measurement for 190 samples were done on our instrument, and on a commercial lab using LC-MS/MS (Mayo Laboratories, USA) for comparison. Results: Our measurements of PAC and PRA was sensitive with a limit of quantification at 3 ng/dL and 0.25 ng/ml/h, respectively, and analytical run times were 6.5 min and 3.5 min, respectively. Both aldosterone and angiotensin 1 calibration curves had excellent linearity in the ranges of 3 - 300 ng/dL and 0.25 - 25 ng/ml/h, respectively, with coefficient of correlation, r2 > 0.994. The intra and inter day accuracy of aldosterone and angiotensin 1 were in the range of 95–110% with CV of < 13%. Reference ranges were established for our local population. Compared with the other LC-MS/MS laboratory, there was good correlation for PAC, r2 = 0.90, 95%CI: 0.86 - 0.92, and PRA, r2 = 0.81, 95% CI: 0.75 - 0.86, using 190 samples. In addition, amongst those with low aldosterone < 6ng/dL, there was good agreement between both labs, with 95 of 122 (77.9%) samples having low aldosterone using both methods, which has been shown to be an ideal threshold to exclude the diagnosis of PA. Conclusions: Our laboratory has developed and validated a sensitive and accurate LC-MS/MS test for PAC and PRA with shortened run time, for the diagnosis PA.