Indian Journal of Critical Care Medicine

Register      Login



Volume / Issue

Online First

Related articles

VOLUME 15 , ISSUE 1 ( January, 2011 ) > List of Articles


Electrolytes assessed by point-of-care testing - Are the values comparable with results obtained from the central laboratory?

John Victor Peter, Shalom Patole, Ratnasamy Selvakumar

Keywords : Agreement, bland and altman, concordance, electrolytes, point-of-care testing

Citation Information : Peter JV, Patole S, Selvakumar R. Electrolytes assessed by point-of-care testing - Are the values comparable with results obtained from the central laboratory?. Indian J Crit Care Med 2011; 15 (1):24-29.

DOI: 10.4103/0972-5229.78219

License: CC BY-ND 3.0

Published Online: 01-06-2018

Copyright Statement:  Copyright © 2011; The Author(s).


Background and Aims: When dealing with very sick patients, the speed and accuracy of tests to detect metabolic derangements is very important. We evaluated if there was agreement between whole blood electrolytes measured by a point-of-care device and serum electrolytes measured using indirect ion-selective electrodes. Materials and Methods: In this prospective study, electrolytes were analyzed in 44 paired samples drawn from critically ill patients. Whole blood electrolytes were analyzed using a point-of-care blood gas analyzer and serum electrolytes were analyzed in the central laboratory on samples transported through a rapid transit pneumatic system. Agreement was summarized by the mean difference with 95% limits of agreement (LOA) and Lin′s concordance correlation (p c). Results: There was a significant difference in the mean (±standard deviation) sodium value between whole blood and serum samples (135.8 ± 5.7 mmol/L vs. 139.9 ± 5.4 mmol/L, P < 0.001), with the agreement being modest (p c = 0.71; mean difference -4.0; 95% LOA -8.78 to 0.65). Although the agreement between whole blood and serum potassium was good (p c = 0.96), and the average difference small (-0.3; 95% LOA -0.72 to 0.13), individual differences were clinically significant, particularly at lower potassium values. For potassium values <3.0 mmol/L, the concordance was low (p c = 0.53) and the LOA was wide (1.0 to -0.13). The concordance for potassium was good (p c = 0.96) for values ≥3.0 (mean difference -0.2; 95% LOA -0.48 to 0.06). Conclusions: Clinicians should be aware of the difference between whole blood and serum electrolytes, particularly when urgent samples are tested at point of care and routine follow-up electrolytes are sent to the central laboratory. A correction factor needs to be determined at each center.

PDF Share
  1. Cox CJ. Acute care testing Blood gases and electrolytes at the point of care. Clin Lab Med 2001;21:321-35.
  2. Morimatsu H, Rocktäschel J, Bellomo R, Uchino S, Goldsmith D, Gutteridge G. Comparison of point-of-care versus central laboratory measurement of electrolyte concentrations on calculations of the anion gap and the strong ion difference. Anesthesiology 2003;98:1077-84.
  3. Prichard JS, French JS, Alvar N. Clinical evaluation of the ABL-77 for point-of-care analysis in the cardiovascular operating room. J Extra Corpor Technol 2006;38:128-33.
  4. Jacobs E, Ancy JJ, Smith M. Multi-site performance evaluation of pH, blood gas, electrolyte, glucose, and lactate determinations with the GEM Premier 3000 critical care analyzer. J Near Pat Test Techno 2002;1:135-44.
  5. Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res 1999;8:135-60.
  6. Lin LI. A concordance correlation coefficient to evaluate reproducibility. Biometrics 1989;45:255-68.
  7. Scott MG, LeGrys VA, Klufts JC. Electrolytes and Blood gases, Ch. 27. In: Burtis CA, Ashwood Er, Bruns DE, editors. Tietz Textbook of Clinical Chemistry. 4th ed. Missouri USA: Elsevier; 2006. p. 985.
  8. Ingram Rh Jr, Seki M. Pseudohyperkalemia with thrombocytosis. N Engl J Med 1962;267:895-900.
  9. Weaver DK, Miller D, Leventhal EA, Tropeano V. Evaluation of a computer-directed pneumatic-tube system for pneumatic transport of blood specimens. Am J Clin Pathol 1978;70:400-5.
  10. D′Orazio P, Burnett RW, Fogh-Andersen N, Jacobs E, Kuwa K, Külpmann WR, et al. Approved IFCC recommendation on reporting results for blood glucose (abbreviated). Clin Chem 2005;51:1573-6.
  11. 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;2:117-20.
PDF Share
PDF Share

© Jaypee Brothers Medical Publishers (P) LTD.