Plasma sodium measurements by direct ion selective methods in laboratory and point of care may not be clinically interchangeable.
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.
Mater Health Services, Stanley Street, South Brisbane, Brisbane, QLD, 4101, Australia.
Brigit A
BA
Weld
Mater Research - University of Queensland, Mater Health Services, Stanley Street, South Brisbane, Brisbane, QLD, 4101, Australia. t.morgan@uq.edu.au.|Intensive Care Unit, Mater Health Services, Stanley Street, South Brisbane, Brisbane, QLD, 4101, Australia. t.morgan@uq.edu.au.
Thomas J
TJ
Morgan
Intensive Care Unit, Royal Melbourne Hospital and University of Melbourne, Parkville, VIC, Australia.
Jeffrey J
JJ
Presneill
Faculty of Health, School of Biomedical Sciences, Queensland University of Technology, Garden Point, Brisbane, QLD, 4101, Australia.
Steven
S
Weier
Mater Research - University of Queensland, Mater Health Services, Stanley Street, South Brisbane, Brisbane, QLD, 4101, Australia.
David
D
Cowley
D019411:Clinical Laboratory Techniques; D003422:Critical Care; D004566:Electrodes; D006801:Humans; D007010:Hyponatremia / Q000175:diagnosis; D007362:Intensive Care Units; D007477:Ions; D016014:Linear Models; D019095:Point-of-Care Systems; D012016:Reference Values; D015203:Reproducibility of Results; D012964:Sodium / Q000097:blood*
D007477:Ions; D012964:Sodium
Accuracy; Data; Data quality; Direct ion selective; Instrumentation; Ion selective electrodes; Measurement; Protein; Sodium; Test–retest reliability
BMC Anesthesiol. 2012 Aug 03;12:17
22862792
Ann Clin Biochem. 2002 Jan;39(Pt 1):66-7
11853193
Lancet. 1986 Feb 8;1(8476):307-10
2868172
Semin Nephrol. 2009 May;29(3):282-99
19523575
Am J Emerg Med. 1985 May;3(3):236-9
3994801
Clin Chem Lab Med. 2000 Oct;38(10):1065-71
11140625
J Crit Care. 2012 Jun;27(3):326.e9-16
22227082
Clin Chem. 1978 Feb;24(2):212-22
627051
Int J Emerg Med. 2009 Feb 24;2(2):117-20
20157454
Ann Clin Biochem. 2011 Sep;48(Pt 5):393-409
21795407
Anesth Analg. 2007 Apr;104(4):893-7
17377102
Scand J Clin Lab Invest. 2015 Apr;75(2):97-105
25431133
Clin Chim Acta. 2010 Mar;411(5-6):309-17
20004654
J Appl Physiol (1985). 1998 May;84(5):1740-8
9572825
Nephrol Dial Transplant. 2014 Apr;29 Suppl 2:i1-i39
24569496
Scand J Clin Lab Invest Suppl. 1996;224:179-86
8865434
N Engl J Med. 2000 May 25;342(21):1581-9
10824078
J Am Soc Nephrol. 1994 Feb;4(8):1522-30
8025225
Clin Chem. 2011 Aug;57(8):1108-17
21677092
N Engl J Med. 2000 May 18;342(20):1493-9
10816188