Should total calcium be adjusted for albumin? A retrospective observational study of laboratory data from central Norway

ObjectivesAlbumin-adjusted total calcium is often used as a surrogate marker for free calcium to evaluate hypocalcaemia or hypercalcaemia. Many adjustment formulas based on simple linear regression models have been published, and continue to be used in spite of questionable diagnostic accuracy. In t...

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Bibliographic Details
Published in:BMJ open 2018-04, Vol.8 (4), p.e017703-e017703
Main Authors: Lian, Ingrid Alsos, Åsberg, Arne
Format: Article
Language:English
Subjects:
Accuracy
Adolescent
Adult
Age
Aged
Aged, 80 and over
Automation
Calcium - blood
Child
Creatinine
Diabetes and Endocrinology
Female
Gases
Glomerular Filtration Rate
Hemodialysis
Humans
Laboratories
Male
Methods
Middle Aged
Norway
Observational studies
Patients
Retrospective Studies
Serum Albumin
Young Adult
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Summary:ObjectivesAlbumin-adjusted total calcium is often used as a surrogate marker for free calcium to evaluate hypocalcaemia or hypercalcaemia. Many adjustment formulas based on simple linear regression models have been published, and continue to be used in spite of questionable diagnostic accuracy. In the hope of finding a more pure albumin effect on total calcium, we used multiple linear regression models to adjust for other relevant variables. The regression coefficients of albumin were used to construct local adjustment formulas, and we tested whether the diagnostic accuracy was improved compared with previously published formulas and unadjusted calcium.DesignA retrospective hospital laboratory data study.Data sourcesThe local hospital laboratory data system.SettingNorway, 2006–2015.Participants6549 patients above 2 years of age, where free calcium standardised at pH 7.40, total calcium, creatinine, albumin and phosphate had been analysed in a single blood draw, including hospitalised patients and patients from outpatient clinics and general practice.Main outcome measuresDiagnostic accuracy by Harrell’s c and receiver operating characteristic curve analysis, using free calcium standardised at pH 7.40 as a gold standard, in subgroups with estimated glomerular filtration rate (eGFR) ≥60 or
ISSN:2044-6055
2044-6055
DOI:10.1136/bmjopen-2017-017703