Plasma Renin Activity (PRA) By LC-MS/MS--Prevention of Reporting Falsely Low Renin Activities

Program: Abstracts - Orals, Poster Previews, and Posters
Session: SAT 572-592-Renin-Angiotensin-Aldostrone System/Endocrine Hypertension (posters)
Saturday, April 2, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board SAT 572
Zengru Wu*1, Shannon Haymond2, Nigel J. Clarke1, Michael Phillip Caulfield1, Richard E. Reitz1 and Michael J. McPhaul1
1Quest Diagnostics Nichols Institute, San Juan Capistrano, CA, 2Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicage, IL
The measurement of angiotensin (Ang) I by radioimmunoassay (RIA) as a surrogate for renin activity was first reported by Sealy and Laragh in 1975 (1). To improve laboratory workflow and throughput, Quest Diagnostics developed an LC-MS/MS based assay in 2009 (2). Unlike conventional isotope dilution LC-MS/MS assays, this assay included the use of an isotope-labeled degradation standard (DS) to monitor the stability of Ang I. Here, we present how the use of DS prevented the reporting of falsely low results caused by wrong specimen types. 

 When the assay was developed, use of the DS identified a subgroup of patient samples that had strong Ang I degradation activity during the 3-hour incubation (2). Initial observations in method validation and clinical testing indicated that approximately 2% to 5% of patient specimens had this “fast degradation” activity. These degradation activities were characterized as a patient-specific phenomenon; however, in operation, some patients did not show degradation activities over different draw times. During the investigation of the root cause for this inconsistency, we measured the calcium concentrations and some samples were found to have normal calcium levels, which was inconsistent with the only acceptable specimen type (EDTA plasma) for this assay. Submission of an incorrect sample type (eg, serum) could explain both strong degradation activities and uncharacteristically low levels of PRA.  A process change was implemented to check the calcium level of all fast-degrader samples using a SofChek strip. If the calcium concentration was inconsistent with an EDTA plasma sample, the test was cancelled with a “wrong specimen type” message. Following a general client and internal communication that reinforced the correct specimen type requirement, the cancellation rate dropped significantly for all samples submitted to Quest Diagnostics for PRA testing. Currently, only 0.1% of all samples submitted for PRA testing are canceled due to a fast-degrader phenotype. This study indicated that in large scale operation, a substantial percentage (2% to 5%) of PRA specimen can be wrong specimen type. The RIA and conventional mass spectrometry assay without DS would unknowingly release falsely low results. The use of DS or a dip stick specimen type check would prevent reporting falsely low results and make the PRA assay more reliable in patient care.

(1) Sealey et al., SeminNucl Med 1975; 5: 189-202. (2) Bystrom et al., Clin Chem 2010;56:1561–9.

Disclosure: ZW: Employee, Quest Diagnostics. NJC: Employee, Quest Diagnostics. MPC: Employee, Quest Diagnostics. RER: Employee, Quest Diagnostics. MJM: Medical Director, Quest Diagnostics Inc.. Nothing to Disclose: SH

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