Endocrine Abstracts

Background: Volumetric absorbent microsampling (VAMS) provides a less intrusive alternative to venepuncture when collecting blood samples for diagnostic testing. A small, precisely determined amount of capillary blood from a single finger-prick is absorbed into a medium for storage, from which it can later be extracted and analysed. In this study, we developed methods to measure four commonly requested endocrine/bone biomarkers for finger-prick blood samples analysis, and investigate the difference in concentration values obtained from venous blood.

Methods: Paired capillary blood samples collected from finger prick using Mitra® VAMS devices (Neoteryx, Torrance, USA) and EDTA plasma from venepuncture (BD vacutainer) were obtained from 44 consented healthy adults from the British Army. LC-MSMS was used to measure 25OHD, testosterone and cortisol; the latter two were analysed by a newly developed Amplifex-keto derivatisation to enhance assay sensitivity. Carboxy-terminal cross-linking telopeptide of type I collagen (β-CTX) was determined by COBAS 6000 e601 using electro-chemiluminescence immunoassay (ECLIA) (Roche). VAMS results were adjusted by haematocrit measurements prior to comparison with plasma values.

Results: Our LC-MSMS method with derivatisation showed inter-and intra-assay precision (%CV) between 3.9-11.6% across testosterone range 0.1-39.9 nmol/L; cortisol was 3.9-8.9% across the range 10-806 nmol/l. Spiked recovery was 97-104%. Passing-Bablok regression showed correlation between the two sample types: cortisol (y=0.8828x+63.004, r²=0.85), testosterone (y=1.1683x+0.407, r²=0.92), 25OHD (y=1.1367x-8.0091, r²=0.83), β-CTX (y=1.1367x-8.0091, r²=0.83). Bland-Altman plots showed average bias(95%CI) against plasma; cortisol -0.91(-6.6 to +1.6)nmol/l, testosterone female +0.1(-0.13 to +0.3), male +4.3(-4.2 to +7.2)nmol/l, 25OHD +1.9(-1.6 to +6.9) nmol/l, β-CTX 0.05(-0.095 to +0.082)µg/l.

Conclusion: The capillary blood concentration of the analytes we tested showed correlation with venous samples. Our finding supports the use of finger prick bloods and Mitra® VAMS device has shown its potential to be an alternative to venepuncture.