Precision Prediction & Precision Medicine


Kitty de Leur, Charlotte Vollenbrock, Pim Dekker, Martine de Vries, Erwin Birnie, Dick Mul, Bruce H. R. Wolffenbuttel, Joost Groen, Henk-Jan Aanstoot, Lianne Boesten

How low is really low? Comparison of two C-peptide assays to establish residual C-peptide production in type 1 diabetes. Diabet Med. 2022 May;39(5):e14785.

Depending on genetic and environmental factors, many people with type 1 diabetes retain some residual β-cell function (i.e. insulin production), sometimes persisting for many years. Furthermore, residual β-cell function has been shown to correlate with better regulation and fewer complications. Since people with type 1 diabetes administer exogenous insulin, residual β-cell function cannot be assessed by measuring insulin. During the production of insulin, proinsulin is cleaved into insulin and C-peptide, which are excreted into the blood in equal levels. Also, C-peptide has a longer half-life, providing a more stable test window. Therefore, measuring stimulated C-peptide production is commonly used as proxy for residual β-cell function. It is becoming increasingly clear that even very low levels of C-peptide (i.e. insuline production) are associated with better outcomes and C-peptide assays are increasingly used near their detection limits.

To measure serum C-peptide a wide range of assays are currently available. For the Biomarker project we considered to switch from the immunoradiometric (IRMA) assay by Beckman, used in our clinical laboratory (IJsselland Hospital) to an ultrasensitive enzyme-linked immunosorbent (ELISA) assay by Mercodia, which should have a lower detection limit according to the manufacturer. The two assays were compared in verification experiments with samples from the Biomarker project.


Key findings:

  • The Beckman IRMA showed a lower detection limit than the Mercodia ELISA
  • The manufacturer-specified limit of detection could not be reproduced for the Mercodia ELISA whereas the Beckman exceeded the manufacturer’s specification
  • Based on the results it was decided to keep using the Beckman IRMA

Concluding, the authors state

"Our results demonstrate the importance of in-house verification of manufacturer-specified performance of laboratory assays, especially when used for a new indication for which clinically meaningful results are outside of the previously used range" -

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