American Diabetes Association
R.DC23-1379._Online-only_Supplemental_Materials.pdf (561.59 kB)

Transdermal blood sampling for C-peptide is a minimally invasive, reliable alternative to venous sampling in children and adults with type 1 diabetes

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posted on 2023-12-13, 00:10 authored by Rachel EJ Besser, Anna E. Long, Katharine R. Owen, Rebecca Law, Jacqueline S Birks, Olivia Pearce, Claire L Williams, Claire L Scudder, Timothy J. McDonald, John A Todd

Objective: C-peptide and islet autoantibodies are key type 1 diabetes biomarkers, typically requiring venous sampling, which limit their utility. We assessed transdermal capillary blood (TCB) collection as a practical alternative.

Research Design and methods: Ninety-one individuals (71 type 1 diabetes, 20 controls; type 1 diabetes: aged median 14.8 years[interquartile range 9.1-17.1]; diabetes duration 4.0 years[1.5-7.7]; controls 42.2 years[38.0-52.1]) underwent contemporaneous venous and TCB sampling for measurement of plasma C-peptide. Type 1 diabetes participants also provided venous serum and plasma, and TCB plasma for measurement of autoantibodies to glutamate decarboxylase, islet antigen-2, and zinc transporter 8. The ability of TCB plasma to detect significant endogenous insulin secretion (venous C-peptide ≥200pmol/L) was compared along with agreement in levels using Bland-Altman. Venous serum was compared with venous and TCB plasma for detection of autoantibodies using established thresholds. Acceptability was assessed by age-appropriate questionnaire.

Results: Transdermal sampling took a mean of 2.35minutes (SD 1.49). Median sample volume was 50 µl(IQR 40-50) with 3/91(3.3%) failures, and 13/88(14.7%) <35 µL). TCB C-peptide showed good agreement to venous plasma (mean venous ln(C-peptide) – TCB ln(C-peptide) = 0.008, 95% CI(-0.23, 0.29), with 100%(36/36) sensitivity/100%(50/50) specificity to detect venous C-peptide ≥ 200pmol/L. Where venous serum in multiple autoantibody positive TCB plasma agreed in 22/32 (sensitivity 69%), comparative specificity was 35/36 (97%). TCB was preferred to venous sampling (type 1 diabetes: 63% vs 7%; 30% undecided).

Conclusions: Transdermal capillary testing for C-peptide is a sensitive, specific, and acceptable alternative to venous sampling, TCB sampling for islet autoantibodies needs further assessment.


This study was supported by grants from the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre (BRC), which also supported funding of R.E.J.B. and K.R.O. R.E.J.B., J.A.T. and C.S. are also funded through the JDRF/Wellcome’s Strategic Award (4-SRA-2017-473-A-N and 107212/A/15/Z). The content and views expressed are those of the author(s) and not necessarily those of the National Health Service, the NIHR. Your bio provided 50 TAP devices at no extra cost. A.E.L. and O.B. were funded through a Diabetes UK and JDRF RD Lawrence Fellowship (18/0005778 and 3‐APF‐2018‐591‐A‐N), and C.W. was funded through Diabetes UK PhD studentship and postdoctoral (16/0005556 and 21/0006332).


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