Background and Aims

C-peptide (CP) is a useful measure in type 1 diabetes (T1D) to assess interventions to preserve beta cell function, risk progression in pre-clinical T1D and diabetes etiology. Venous sampling is limited due to practical considerations, including invasive sampling, limited access to phlebotomy, shielding patients, and remote consultations. We assessed plasma CP collected from a transdermal capillary blood (TCB) device as a practical alternative.

Methods

71 children and adults with T1D (median age 14.8y(IQR 9.1-17.7), diabetes duration 4.0y(1.5-7.7)) and 20 controls (age 42.2y(IQR:38.0-52.1) had a concomitant venous and TCB sample collected for measurement of plasma CP. Acceptability was assessed by age-appropriate questionnaires.

Results

Venous plasma CP was assessed across a wide range of values (median=45.5pmol/L, IQR(<3.3, 626), range (<3pmol/L, 2792). Median TCB plasma volume was 50uL(IQR 40, 50). TCB plasma CP was highly correlated to venous plasma CP (correlation coefficient=0.996). TCB CP had 100% sensitivity and 98% specificity to detect venous CP >200pmol/L.

Children and adults with T1D self-reported higher pain scores for venous compared to TCB sampling (<16y: 2/10 venous vs 1.1/10 TCB, 0=no pain, 10=very painful); >16y: 2.9/7 vs 1.2/7, 1=no pain, 7=very painful). T1D participants preferred TCB over venous sampling (63% (44/70) vs 7% (5/70)); 30% (21/70) were undecided.

Conclusions

Transdermal collection for C-peptide is a highly sensitive and specific method for detecting endogenous insulin production and is a preferred method in children, young people and adults with type 1 diabetes compared to venous sampling. TCB may be a practical alternative to venous sampling for C-peptide, avoiding the need to access a healthcare professional for traditional venepuncture.