Inter-instrumental comparison for the measurement of electrolytes in patients admitted to the intensive care unit

Abstract

ObjectiveTo investigate whether benchtop auto-analyzers (AAs) and arterial blood gas (ABG) analyzers, for measuring electrolyte levels of patients admitted to intensive care units (ICU), are equal and whether they can be used interchangeably.Materials and methodThis study was conducted on 98 patients admitted to the ICU of the Institute of Medicine, Kathmandu, Nepal between 15 October and 15 December 2016. The sample for AA was collected from the peripheral vein through venipuncture, and that for ABG analyzer was collected from radial artery simultaneously. Electrolyte levels were measured with ABG analyzer in the ICU itself, and with benchtop AA in the central clinical biochemistry laboratory.ResultsThe mean value for sodium by AA was 144.6 (standard deviation [SD] 7.63) and by ABG analyzer 140.1 (SD 7.58), which was significant (p-value <0.001). The mean value for potassium by AA was 3.6 (SD 0.52) and by ABG analyzer 3.58 (SD 0.66). The Bland-Altman analysis with the 95% limit of agreement between methods were −4.45 to 13.11 mmol/L for sodium and the mean difference was 4.3 mmol/L and −1.15 to 1.24 mmol/L for potassium and the mean difference was 0.04 mmol/L. The United States Clinical Laboratory Improvement Amendments accepts a 0.5 mmol/L difference in measured potassium levels and a 4 mmol/L difference in measured sodium levels, in the gold standard measure of the standard calibration solution. The passing and Bablok regression with 95% confidence interval has an intercept of zero and slope one for both sodium and potassium, and the 95% of random difference is −6.32 to 6.32 for sodium and −0.84 to 0.84 for potassium, showing no significant deviation from linearity.ConclusionIt can be concluded that AA and ABG analyzers may be used interchangeably for measurement of potassium in the Institute of Medicine, while the same cannot be concluded for the measurement of sodium, because of the significant difference in sodium measurement by the two instruments.

Determination of Electrolytes in Critical Illness Patients at Different pH Ranges: Whom Shall We Believe, the Blood Gas Analysis or the Laboratory Autoanalyzer?

“…These results are generally in line with previously published data [15]. However, amongst other studies, Budak et al found out that even potassium test results obtained using an ABG and an AA differ and the data thus cannot be used interchangeably in clinical practice [20].…”

“…These previously observed differences between the electrolyte levels measured using an AA and ABG analyzer may be explained on the basis of a combination of factors such as sample transport, dilution determinants, or instrument calibration. For instance, it is well known that ISE-based analysis devices from different manufacturers yield sodium/potassium levels that differ by 2–5% [15]. Moreover, for various types of heparin in blood gas syringes, a preanalytical bias in electrolyte concentrations was demonstrated.…”

A validation study of microscopy versus quantitative PCR for measuring Plasmodium falciparum parasitemia

“…Parasitemia values from microscopy and from 18S qPCR showed good agreement and no evidence of systematic or proportional bias by Passing–Bablok regression, a method commonly used in clinical laboratory settings [14]. Our findings of a mean difference of 0.04 log 10 units/mL are supported by several smaller studies.…”

A method comparison study of a point-of-care blood gas analyser with a laboratory auto-analyser for the determination of potassium concentrations during hyperkalaemia in patients with kidney disease

“…This may have been diminished or absent if the full range of potassium concentrations were evaluated. Previous studies that included samples across a wider range of potassium concentrations did not report any proportional systematic error ( 22 - 24 ).…”