Assessing vitamin D nutritional status: Is capillary blood adequate?

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 10 days after receiving 100,000 IU of vitamin-D-3 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 255 nmol/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. Conclusion: 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. (C) 2016 Elsevier B.V. All rights reserved.