C-peptide production is commonly used as proxy for residual β-cell function and measuring it is becoming increasingly important in diabetes research. 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 commercial assays are currently available. However, not all assays yield consistent results, especially in the low concentration ranges. Earlier we reported on a comparison between two C-peptide assays, showing that one of the assay did not meet the manufacturer’s specifications. This prompted us to evaluate in the literature which C-peptide assays are currently available and to what extent information is provided about these assays used in publications in the diabetes research field.

We searched PubMed with the search terms ‘assay’, ‘C-peptide’ and ‘diabetes’ between 01-01-2016 and 31-12-2020, only including publications in the English language. Of 1,289 eligible publications, 515 were included.

Key findings:

• Percentages of publications on C-peptide measurements in type 1 diabetes (T1D), type 2 diabetes (T2D) and other forms of diabetes were 32%, 54% and 14%, respectively.
• In only 54% of the publications the used assay was specified. Information on detection limit, measurement range and variation was provided in 12%, 2% and 11% of publications, respectively.
• In 22% of all publications no C-peptides concentrations were mentioned.
• Most C-peptide measurements in the diabetes research field are performed with chemiluminescence immunoassays from Roche, Siemens and Tosoh.
• Mercodia is the most frequently mentioned manufacturer in the T1D field. After chemiluminescent assays, ELISA is the most commonly used methodology.

Concluding, the authors state that

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