title: Assessing vitamin D nutritional status: Is capillary blood adequate?
abstract: BACKGROUND
  Venous blood is the usual sample for measuring various biomarkers, including 25-hydroxyvitamin D (25OHD). However, it can prove challenging in infants and young children. Hence the finger-prick capillary collection is an alternative, being a relatively simple procedure perceived to be less invasive. We elected to validate the use of capillary blood sampling for 25OHD quantification by liquid chromatography tandem-mass spectrometry (LC/MS-MS).
  
  
  METHODS
  Venous and capillary blood samples were simultaneously collected from 15 preschool-aged children with asthma 10days after receiving 100,000IU of vitamin-D3 or placebo and 20 apparently healthy adult volunteers. 25OHD was measured by an in-house LC/MS-MS method.
  
  
  RESULTS
  The venous 25OHD values varied between 23 and 255nmol/l. The venous and capillary blood total 25OHD concentrations highly correlated (r(2)=0.9963). The mean difference (bias) of capillary blood 25OHD compared to venous blood was 2.0 (95% CI: -7.5, 11.5) nmol/l.
  
  
  CONCLUSIONS
  Our study demonstrates excellent agreement with no evidence of a clinically important bias between venous and capillary serum 25OHD concentrations measured by LC/MS-MS over a wide range of values. Under those conditions, capillary blood is therefore adequate for the measurement of 25OHD.
authors.affiliation: Centre for Asthma and Respiratory Diseases, School of Biomedical Sciences, School of Medicine and Public Health, University of Newcastle, Callaghan, Australia.
authors.forename: M E
authors.initials: ME
authors.lastname: Jensen
authors.affiliation: Departments of Pediatrics and Social and Preventive Medicine, University of Montreal, Canada; Clinical Research and Knowledge Transfer Unit, Research Centre, CHU Ste-Justine, Montreal, Canada.
authors.forename: F M
authors.initials: FM
authors.lastname: Ducharme
authors.affiliation: Clinical Pharmacology Unit, Department of Clinical Biochemistry, CHU Ste-Justine, Canada; Department of Pharmacology, University of Montreal, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Théorêt
authors.affiliation: Department of Clinical Biochemistry, CHU Ste-Justine, Canada.
authors.forename: A-S
authors.initials: AS
authors.lastname: Bélanger
authors.affiliation: Gatroenterology, Hepatology & Nutrition Division, CHU Ste-Justine Research Centre, University of Montreal, Canada. Electronic address: delvine@sympatico.ca.
authors.forename: E
authors.initials: E
authors.lastname: Delvin
mesh_terms: D002853:Chromatography, Liquid; D006801:Humans; D009752:Nutritional Status; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000097:blood*
chemical_list: D014807:Vitamin D
keywords: 25-Hydroxyvitamin D; Capillary blood; Tandem mass spectrometry; Venous blood