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Point-of-care testing of electrolytes and calcium using blood gas analysers: it is time we trusted the results
  1. Mehdi Mirzazadeh,
  2. Alireza Morovat,
  3. Tim James,
  4. Ian Smith,
  5. Justin Kirby,
  6. Brian Shine
  1. Department of Clinical Biochemistry, John Radcliffe Hospital, Oxford, UK
  1. Correspondence to Dr Mehdi Mirzazadeh, Department of Clinical Biochemistry, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK; Mehdi.mirzazadeh{at}ouh.nhs.uk

Abstract

Background Point-of-care testing allows rapid analysis of samples to facilitate prompt clinical decisions. Electrolyte and calcium abnormalities are common in acutely ill patients and can be associated with life-threatening consequences. There is uncertainty whether clinical decisions can be based on the results obtained from blood gas analysers or if laboratory results should be awaited.

Objectives To assess the agreement between sodium, potassium and calcium results from blood gas and laboratory mainstream analysers in a tertiary centre, with a network consisting of one referral and two peripheral hospitals, consisting of three networked clinical biochemistry laboratories.

Method Using the laboratory information management system database and over 11 000 paired samples in three hospital sites, the results of sodium, potassium and ionised calcium on blood gas analysers were studied over a 5-year period and compared with the corresponding laboratory results from the same patients booked in the laboratory within 1 h.

Results The Pearson's linear correlation coefficient between laboratory and blood gas results for sodium, potassium and calcium were 0.92, 0.84 and 0.78, respectively. Deming regression analysis showed a slope of 1.04 and an intercept of −5.7 for sodium, slope of 0.93 and an intercept of 0.22 for potassium and a slope of 1.23 with an intercept of −0.55 for calcium. With some strict statistical assumptions, percentages of results lying outside the least significant difference were 9%, 26.7% and 20.8% for sodium, potassium and calcium, respectively.

Conclusions Most clinicians wait for the laboratory confirmation of results generated by blood gas analysers. In a large retrospective study we have shown that there is sufficient agreement between the results obtained from the blood gas and laboratory analysers to enable prompt clinical decisions to be made.

  • interpretation
  • diagnosis
  • clinical management
  • errors
  • metabolic/diabetes/endocrine

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