Errors of Classification With Potassium Blood Testing: The Variability and Repeatability of Critical Clinical Tests

Paul Andrew Friedman, Christopher G. Scott, Kent R Bailey, Nikola A. Baumann, David Albert, Zachi I. Attia, Dorothy J. Ladewig, Omar Yasin, John J. Dillon, Bhupinder Singh

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Objective: To understand the performance of a currently used clinical blood test with regard to the frequency and size of variation of the results. Patients and Methods: From November 29, 2012, through November 29, 2013, patients were recruited at 65 sites as part of a previously reported clinical trial (ClinicalTrials.gov Identifier: NCT01737697). Eligible outpatients who had been fasting for at least 8 hours underwent venous phlebotomy at baseline, 30 minutes, and 60 minutes to measure plasma potassium levels in whole blood using a point-of-care device (i-STAT, Abbott Laboratories). We analyzed the results to assess their variability and frequency of pseudohyperkalemia and pseudonormokalemia. Results: A total of 1170 patients were included in this study. Absolute differences between pairs of measurements from different time points ranged from 0 to 2.5 mmol/L, with a mean difference of 0.26 mmol/L. The mean percentage differences were approximately 5% with an SD of 5%. Approximately 12% of differences between repeated fasting potassium blood test results were above 0.5 mmol/L (33% of the normal range), and 20% of patients (234) had at least one difference greater than 0.5 mmol/L. In 44.0% of the patients with a hyperkalemic average value (true hyperkalemia) (302 of 686), at least one blood test result was in the normal range (pseudonormokalemia), and in 30.2% of the patients with a normal average value (146 of 484), at least one blood test result was elevated (pseudohyperkalemia). Conclusion: Expected variability and errors exist with potassium blood tests, even when conditions are optimized. Pseudohyperkalemia and pseudonormokalemia are common, indicating a need for thoughtful clinical interpretation of unexpected test results.

Original languageEnglish (US)
Pages (from-to)566-572
Number of pages7
JournalMayo Clinic Proceedings
Volume93
Issue number5
DOIs
StatePublished - May 1 2018

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Hematologic Tests
Potassium
Reference Values
Fasting
Point-of-Care Systems
Hyperkalemia
Phlebotomy
Outpatients
Clinical Trials
Equipment and Supplies

ASJC Scopus subject areas

  • Medicine(all)

Cite this

Errors of Classification With Potassium Blood Testing : The Variability and Repeatability of Critical Clinical Tests. / Friedman, Paul Andrew; Scott, Christopher G.; Bailey, Kent R; Baumann, Nikola A.; Albert, David; Attia, Zachi I.; Ladewig, Dorothy J.; Yasin, Omar; Dillon, John J.; Singh, Bhupinder.

In: Mayo Clinic Proceedings, Vol. 93, No. 5, 01.05.2018, p. 566-572.

Research output: Contribution to journalArticle

Friedman, Paul Andrew ; Scott, Christopher G. ; Bailey, Kent R ; Baumann, Nikola A. ; Albert, David ; Attia, Zachi I. ; Ladewig, Dorothy J. ; Yasin, Omar ; Dillon, John J. ; Singh, Bhupinder. / Errors of Classification With Potassium Blood Testing : The Variability and Repeatability of Critical Clinical Tests. In: Mayo Clinic Proceedings. 2018 ; Vol. 93, No. 5. pp. 566-572.
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AU - Scott, Christopher G.

AU - Bailey, Kent R

AU - Baumann, Nikola A.

AU - Albert, David

AU - Attia, Zachi I.

AU - Ladewig, Dorothy J.

AU - Yasin, Omar

AU - Dillon, John J.

AU - Singh, Bhupinder

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AB - Objective: To understand the performance of a currently used clinical blood test with regard to the frequency and size of variation of the results. Patients and Methods: From November 29, 2012, through November 29, 2013, patients were recruited at 65 sites as part of a previously reported clinical trial (ClinicalTrials.gov Identifier: NCT01737697). Eligible outpatients who had been fasting for at least 8 hours underwent venous phlebotomy at baseline, 30 minutes, and 60 minutes to measure plasma potassium levels in whole blood using a point-of-care device (i-STAT, Abbott Laboratories). We analyzed the results to assess their variability and frequency of pseudohyperkalemia and pseudonormokalemia. Results: A total of 1170 patients were included in this study. Absolute differences between pairs of measurements from different time points ranged from 0 to 2.5 mmol/L, with a mean difference of 0.26 mmol/L. The mean percentage differences were approximately 5% with an SD of 5%. Approximately 12% of differences between repeated fasting potassium blood test results were above 0.5 mmol/L (33% of the normal range), and 20% of patients (234) had at least one difference greater than 0.5 mmol/L. In 44.0% of the patients with a hyperkalemic average value (true hyperkalemia) (302 of 686), at least one blood test result was in the normal range (pseudonormokalemia), and in 30.2% of the patients with a normal average value (146 of 484), at least one blood test result was elevated (pseudohyperkalemia). Conclusion: Expected variability and errors exist with potassium blood tests, even when conditions are optimized. Pseudohyperkalemia and pseudonormokalemia are common, indicating a need for thoughtful clinical interpretation of unexpected test results.

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