PMID- 37391118 OWN - NLM STAT- MEDLINE DCOM- 20230807 LR - 20230807 IS - 1873-2933 (Electronic) IS - 0009-9120 (Linking) VI - 118 DP - 2023 Aug TI - Characterizing ability of serum potassium (K) and the serum K reference interval to flag hypokalemia or hyperkalemia as observed in plasma: A simulation study. PG - 110606 LID - S0009-9120(23)00134-0 [pii] LID - 10.1016/j.clinbiochem.2023.110606 [doi] AB - OBJECTIVES: Serum potassium (K) exhibits a positive shift relative to plasma K due to a variable amount of K release associated with clotting. Because of this variation, plasma K results outside of the reference interval (RI) for plasma (hypokalemia or hyperkalemia) in individual samples may not produce classification-concordant results in serum according to the serum RI. We examined this premise from a theoretical standpoint by simulation. DESIGN & METHODS: We used textbook K reference intervals for plasma (PRI = 3.4-4.5 mmol/L) and serum (SRI = 3.5-5.1 mmol/L). The difference between PRI and SRI is characterized by a normal distribution: serum K = plasma K + 0.35 +/- 0.308 mmol/L. This transformation was applied by simulation to an observed patient data distribution for plasma K to generate a corresponding theoretical serum K distribution. Individual samples were tracked for comparison with respect to classification (below, within, above RI) for plasma and serum. RESULTS: Primary data were an all-comers plasma K patient distribution (n = 41,768; median = 4.1 mmol/L; 7.1% below PRI (hypokalemia); 15.5% above PRI (hyperkalemia)). Simulation to obtain the associated serum K yielded a right-shifted distribution (median = 4.4 mmol/L; 4.8% below SRI; 10.8% above SRI). Sensitivity for detection in serum (flagged below SRI) for samples originating as hypokalemic in plasma was 45.7% (specificity = 98.3%). Sensitivity for detection in serum (flagged above SRI) for samples originating as hyperkalemic in plasma was 56.6% (specificity = 97.6%). CONCLUSIONS: Simulation results indicate that serum K should best be thought of as an inferior substitute marker for plasma K. These results follow simply from the variable component of serum K compared to plasma K. Plasma should be the preferred specimen type for K assessment. CI - Copyright (c) 2023 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. FAU - Stickle, Douglas F AU - Stickle DF AD - Jefferson University Hospital, Philadelphia, PA, USA. Electronic address: douglas.stickle@jefferson.edu. FAU - Koob, K Rebecca AU - Koob KR AD - Jefferson University Hospital, Philadelphia, PA, USA. Electronic address: kristen.koob@jefferson.edu. FAU - McCudden, Christopher R AU - McCudden CR AD - Ottawa Hospital, University of Ottawa, Ottawa, Ontario, Canada. Electronic address: cmccudde@uottawa.ca. LA - eng PT - Journal Article DEP - 20230628 PL - United States TA - Clin Biochem JT - Clinical biochemistry JID - 0133660 RN - RWP5GA015D (Potassium) SB - IM MH - Humans MH - *Hypokalemia MH - *Hyperkalemia/diagnosis MH - Potassium OTO - NOTNLM OT - Hypokalemia/hyperkalemia OT - Plasma/serum OT - Potassium OT - Receiver-operating characteristics OT - Simulation COIS- Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. EDAT- 2023/07/01 11:41 MHDA- 2023/08/07 06:42 CRDT- 2023/06/30 19:18 PHST- 2023/04/17 00:00 [received] PHST- 2023/06/21 00:00 [revised] PHST- 2023/06/27 00:00 [accepted] PHST- 2023/08/07 06:42 [medline] PHST- 2023/07/01 11:41 [pubmed] PHST- 2023/06/30 19:18 [entrez] AID - S0009-9120(23)00134-0 [pii] AID - 10.1016/j.clinbiochem.2023.110606 [doi] PST - ppublish SO - Clin Biochem. 2023 Aug;118:110606. doi: 10.1016/j.clinbiochem.2023.110606. Epub 2023 Jun 28.