Abstract
An estimated 25 % of indirect ion selective electrode (ISE) ICU plasma sodium measurements differ from corresponding direct ISE values by at least 4 mmol/L, the dominant factor being indirect ISE over-estimation driven by hypoproteinemia. Since direct measurements are considered unaffected by protein concentrations, we investigated whether direct ISE plasma sodium measurements in the laboratory and at point of care in ICU show sufficient agreement to be clinically interchangeable. From a 5 year clinical chemistry database, 9910 ICU plasma samples were assessed for agreement between direct ISE sodium measurements in ICU (ABL 700) and in the central laboratory (Vitros Fusion). The relationship between differences in paired plasma sodium measurements (Vitros–ABL) and total plasma protein concentrations was evaluated by generalized estimating equation linear regression. Patients were hypo-proteinemic [mean (SD) total protein concentration 56.9 (9.04) g/L]. Mean (SD) paired Vitros–ABL sodium measurements was −0.087 (1.74) mmol/L, range −14 to +10 mmol/L. Disagreement at ≥|4|mmol/L, ≥|3|mmol/L and ≥|2|mmol/L was present in 409 (4.1 %), 1333 (13.4 %) and 3591 (36.2 %) pairs respectively. Test–retest disagreement estimates within either source alone were substantially lower. Small negative Vitros–ABL differences associated with low plasma protein concentrations were reversed at high protein concentrations. Disagreement between plasma sodium concentrations monitored by two common direct ISE analyzers was substantially less than reported between direct and indirect ISE devices, although a protein influence of low clinical importance persisted. Disagreement was sufficient to jeopardize safe interchangeable interpretation in situations with a low tolerance for imprecision, such as hyponatremia correction.
Similar content being viewed by others
References
Sterns RH, Cappuccio JD, Silver SM, Cohen EP. Neurologic sequelae after treatment of severe hyponatremia: a multicenter perspective. J Am Soc Nephrol. 1994;4(8):1522–30.
Sterns RH, Nigwekar SU, Hix JK. The treatment of hyponatremia. Semin Nephrol. 2009;29(3):282–99. doi:10.1016/j.semnephrol.2009.03.002.
Adrogue HJ, Madias NE. Hyponatremia. N Engl J Med. 2000;342(21):1581–9. doi:10.1056/NEJM200005253422107.
Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493–9. doi:10.1056/NEJM200005183422006.
White GH. Metrological traceability in clinical biochemistry. Ann Clin Biochem. 2011;48(Pt 5):393–409. doi:10.1258/acb.2011.011079.
Greg Miller W, Myers GL, Lou Gantzer M, Kahn SE, Schonbrunner ER, Thienpont LM, Bunk DM, Christenson RH, Eckfeldt JH, Lo SF, Nubling CM, Sturgeon CM. Roadmap for harmonization of clinical laboratory measurement procedures. Clin Chem. 2011;57(8):1108–17. doi:10.1373/clinchem.2011.164012.
Dimeski G, Badrick T, St John A. Ion selective electrodes (ISEs) and interferences—a review. Clin Chim Acta. 2010;411(5–6):309–17.
Aw TC, Kiechle FL. Pseudohyponatremia. Am J Emerg Med. 1985;3(3):236–9.
Burnett RW, Covington AK, Fogh-Andersen N, Kulpmann WR, Lewenstam A, Maas AH, Muller-Plathe O, Sachs C, Siggaard-Andersen O, VanKessel AL, Zijlstra WG. Recommendations for measurement of and conventions for reporting sodium and potassium by ion-selective electrodes in undiluted serum, plasma or whole blood. International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). IFCC Scientific Division Working Group on Selective Electrodes. Clin Chem Lab Med. 2000;38(10):1065–71. doi:10.1515/CCLM.2000.159.
Story DA, Morimatsu H, Egi M, Bellomo R. The effect of albumin concentration on plasma sodium and chloride measurements in critically ill patients. Anesth Analg. 2007;104(4):893–7. doi:10.1213/01.ane.0000258015.87381.61.
Jain A, Subhan I, Joshi M. Comparison of the point-of-care blood gas analyzer versus the laboratory auto-analyzer for the measurement of electrolytes. Int J Emerg Med. 2009;2(2):117–20. doi:10.1007/s12245-009-0091-1.
Budak YU, Huysal K, Polat M. Use of a blood gas analyzer and a laboratory autoanalyzer in routine practice to measure electrolytes in intensive care unit patients. BMC Anesthesiol. 2012;12:17. doi:10.1186/1471-2253-12-17.
Lang T, Prinsloo P, Broughton AF, Lawson N, Marenah CB. Effect of low protein concentration on serum sodium measurement: pseudohypernatraemia and pseudonormonatraemia! Ann Clin Biochem. 2002;39(Pt 1):66–7.
Dimeski G, Morgan TJ, Presneill JJ, Venkatesh B. Disagreement between ion selective electrode direct and indirect sodium measurements: Estimation of the problem in a tertiary referral hospital. J Crit Care. 2012;27(3):326 e316–29. doi:10.1016/j.jcrc.2011.11.003.
Uyanik M, Sertoglu E, Kayadibi H, Tapan S, Serdar MA, Bilgi C, Kurt I. Comparison of blood gas, electrolyte and metabolite results measured with two different blood gas analyzers and a core laboratory analyzer. Scand J Clin Lab Investig. 2015;75(2):97–105. doi:10.3109/00365513.2014.981854.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307–10.
Westgard JO. Desirable specifications for total error, imprecision, and bias, derived from intra- and inter-individual biologic variation. 2016. https://www.westgard.com/biodatabase1.htm.
Van Steirteghem AC, Robertson EA, Young DS. Variance components of serum constituents in healthy individuals. Clin Chem. 1978;24(2):212–22.
Wilkes P. Hypoproteinemia, strong-ion difference, and acid-base status in critically ill patients. J Appl Physiol. 1998;84(5):1740–8.
USA Clinical Laboratory Improvement Ammendment. Regulations part 493 laboratory requirements, subpart 1 proficiency testing programs by specialty and subspecialty, section 493.931 routine chemistry. 2004.
Spasovski G, Vanholder R, Allolio B, Annane D, Ball S, Bichet D, Decaux G, Fenske W, Hoorn EJ, Ichai C, Joannidis M, Soupart A, Zietse R, Haller M, van der Veer S, Van Biesen W, Nagler E, Hyponatraemia Guideline Development G. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transpl. 2014;29(Suppl 2):i1–39. doi:10.1093/ndt/gfu040.
Maas B, Sprokholt R, Maas A, Fogh-Andersen N. The need for protein containing quality control materials for blood pH and electrolyte analyzers. Scand J Clin Lab Investig. 1996;224:179–86.
Acknowledgments
The authors wish to thank Dr Janet Warner, Director of Chemical Pathology, Mater Health Services Pathology, for helpful assistance and advice.
Funding
Project supported by Departmental Funds.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
The authors declare that they have no competing interests.
Appendix 1
Appendix 1
Hospital laboratory Quality Control (QC) data for Vitros and ABL instruments.
The ABL instruments are traceable to the National Institute of Standards and Technology (NIST) certified Standard Reference Material (SRM) 909b (made from lyophilised human serum) and Radiometer specified standard serum material (specified using flame photometry).
The Vitros slides are traceable to NIST SRM 919a which is pure sodium chloride (specified using flame photometry).
Vitros QC sodium data for mid-2012:
-
Fusion 5.1 (Instrument Vitros 1):
-
at 125 mmol/L, SD = 0.6
-
at 159 mmol/L, SD = 0.8
-
-
Fusion 5.1 (Instrument Vitros 2):
-
at 124 mmol/L, SD = 0.6
-
at 159 mmol/L, SD = 0.8
-
-
Fusion 5600 (Instrument Vitros 3):
-
at 124 mmol/L, SD = 0.7
-
at 159 mmol/L, SD = 0.9
-
ABL analyzer QC data:
-
Instrument ABL1:
-
Na = 160 mmol/L SD = 0.5 mmol/L
-
Na = 142 mmol/L SD = 0.5 mmol/L
-
Na = 128 mmol/L SD = 0.3 mmol/L
-
-
Instrument ABL2:
-
Na = 160 mmol/L SD = 0.6 mmol/L
-
Na = 142 mmol/L SD = 0.6 mmol/L
-
Na = 128 mmol/L SD = 0.6 mmol/L
-
Rights and permissions
About this article
Cite this article
Weld, B.A., Morgan, T.J., Presneill, J.J. et al. Plasma sodium measurements by direct ion selective methods in laboratory and point of care may not be clinically interchangeable. J Clin Monit Comput 31, 1103–1109 (2017). https://doi.org/10.1007/s10877-016-9938-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10877-016-9938-1