Plasma sodium measurements by direct ion selective methods in laboratory and point of care may not be clinically interchangeable

Weld, Brigit A., Morgan, Thomas J., Presneill, Jeffrey J., Weier, Steven and Cowley, David (2016) Plasma sodium measurements by direct ion selective methods in laboratory and point of care may not be clinically interchangeable. Journal of Clinical Monitoring and Computing, 1-7. doi:10.1007/s10877-016-9938-1


Author Weld, Brigit A.
Morgan, Thomas J.
Presneill, Jeffrey J.
Weier, Steven
Cowley, David
Title Plasma sodium measurements by direct ion selective methods in laboratory and point of care may not be clinically interchangeable
Journal name Journal of Clinical Monitoring and Computing   Check publisher's open access policy
ISSN 1573-2614
1387-1307
Publication date 2016-09-28
Sub-type Article (original research)
DOI 10.1007/s10877-016-9938-1
Open Access Status Not yet assessed
Start page 1
End page 7
Total pages 7
Place of publication Dordrecht, Netherlands
Publisher Springer Netherlands
Collection year 2017
Language eng
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.
Keyword Accuracy
Data
Data quality
Direct ion selective
Instrumentation
Ion selective electrodes
Measurement
Protein
Sodium
Test–retest reliability
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Mater Research Institute-UQ (MRI-UQ)
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