Impact of routine clinic measurement of serum C‐peptide in people with a clinician‐diagnosis of type 1 diabetes
Open accessAbstract
Aims/hypothesis: The aim of this study was to determine the impact of the routine use of serum C‐peptide in an out‐patient clinic setting on individuals with a clinician‐diagnosis of type 1 diabetes. Methods: In this single‐centre study, individuals with type 1 diabetes of at least 3 years duration were offered random serum C‐peptide testing at routine clinic review. A C‐peptide ≥200 pmol/L prompted further evaluation of the individual using a diagnostic algorithm that included measurement of islet cell antibodies and genetic testing. Where appropriate, a trial of anti‐diabetic co‐therapies was considered. Results: Serum C‐peptide testing was performed in 859 individuals (90% of the eligible cohort), of whom 114 (13.2%) had C‐peptide ≥200 pmol/L. The cause of diabetes was reclassified in 58 individuals (6.8% of the tested cohort). The majority of reclassifications were to type 2 diabetes (44 individuals; 5.1%), with a smaller proportion of monogenic diabetes (14 individuals; 1.6%). Overall, 13 individuals (1.5%) successfully discontinued insulin, while a further 16 individuals (1.9%) had improved glycaemic control following the addition of co‐therapies. The estimated total cost of the testing programme was £23,262 (~€26,053), that is, £27 (~€30) per individual tested. In current terms, the cost of prior insulin therapy in the individuals with monogenic diabetes who successfully stopped insulin was approximately £57,000 (~€64,000). Conclusions/interpretation: Serum C‐peptide testing can easily be incorporated into an out‐patient clinic setting and could be a cost‐effective intervention. C‐peptide testing should be strongly considered in individuals with a clinician‐diagnosis of type 1 diabetes of at least 3 years duration.
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Routine C-peptide testing in those with clinically diagnosed type 1 diabetes of at least 3 years duration has led to reclassification in 11% of those with adult-onset diabetes.
“Routine C-peptide testing in those with clinically diagnosed type 1 diabetes of at least 3 years duration has led to reclassification in 11% of those with adult-onset diabetes (31).”
From The management of type 1 diabetes in adults. A consensus report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) (2021) · cites this paper as [31]
The Results passage in our copy reports routine C-peptide testing in people with a clinician-diagnosis of type 1 diabetes of at least 3 years’ duration and reclassification in 58 of 859 tested individuals (6.8%). It does not report an 11% reclassification rate for the adult-onset subgroup; searches for that figure and subgroup found no supporting passage. The overall 6.8% figure does not, by itself, contradict a possible subgroup rate. (LLM, conf=0.83)
Experimental — accuracy not yet measuredThe rate of misclassification of type 1 diabetes mellitus increases with age of onset.
“A study looking at the effect of the routine use of serum levels of C-peptide in an outpatient clinic setting on individuals with clinician-diagnosed T1DM showed that the rate of misclassification of T1DM increases with age of onset30.”
From The epidemiology of type 1 diabetes mellitus in older adults (2025) · cites this paper as [30]
The available Results passage reports that 58 of 859 tested individuals (6.8%) had their diabetes reclassified, but gives no rates by age of onset. Searches for age at onset, age at diagnosis, and misclassification found no passage establishing the claimed increase. (LLM, conf=0.70)
Experimental — accuracy not yet measuredMisclassification rates were <1%, 7.2% and 14.2% in those aged <18, 18-30 and >30 years, respectively.
“They found misclassification rates of <1%, 7.2% and 14.2% in those aged <18, 18–30 and >30 years, respectively.”
From The epidemiology of type 1 diabetes mellitus in older adults (2025) · cites this paper as [30]
The Results text in our indexed copy (page unavailable) reports an overall reclassification rate of 6.8%, but gives no rates by age group. Searches for 14.2% and the specified age bands found no passage supporting the three claimed rates. (LLM, conf=0.68)
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Marx, N., Federici, M., Schütt, K., Müller-Wieland, D., Ajjan, R. A., Antunes, M. J., Christodorescu, R. M., Crawford, C., Di Angelantonio, E., Eliasson, B., et al. (2023) · European Heart Journal · doi:10.1093/eurheartj/ehad192 · Cited by 1,642 · see citing works
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The epidemiology of type 1 diabetes mellitus in older adults
Tomic, D., Harding, J. L., Jenkins, A. J., Shaw, J. E., & Magliano, D. J. (2025) · Nature Reviews Endocrinology · doi:10.1038/s41574-024-01046-z · Cited by 58 · see citing works
“A study looking at the effect of the routine use of serum levels of C-peptide in an outpatient clinic setting on individuals with clinician-diagnosed T1DM showed that the rate of misclassification of T1DM increases with age of onset 30 .”
- Authors
- Foteinopoulou, E., Clarke, C. A. L., Pattenden, R. J., Ritchie, S. A., McMurray, E. M., Reynolds, R. M., Arunagirinathan, G., Gibb, F. W., McKnight, J. A., & Strachan, M. W. J.
- Affiliations
- Western General Hospital (GB)
- Edinburgh Royal Infirmary (GB)
- Corresponding author
- Foteinopoulou, Evgenia
- Venue
- Diabetic Medicine
- Publisher
- Wiley
- Published
- 2020-11-22
- Volume
- 38
- Issue
- 7
- Pages
- e14449-e14449
- ISSN
- 0742-3071 (ISSN-L)
- 1464-5491
- OpenAlex
- W3097445394
- Cited by
- 61
- References
- 5
- Citations by year
- 2026: 10 · 2025: 10 · 2024: 9 · 2023: 13 · 2022: 12 · 2021: 7
- FWCI
- 4.69
- Type
- journal article
- Language
- en
- Open access
- Licence
- Locations
- Diabetic Medicine (publishedVersion)
- PubMed (publishedVersion)
- Edinburgh Research Explorer (University of Edinburgh) (publishedVersion, other-oa)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Diabetes and associated disorders
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Diabetes Management and Research
- Health Sciences › Medicine › Surgery › Pancreatic function and diabetes
- Keywords
- type 1 diabetes, type 2 diabetes, monogenic diabetes, islet cell antibodies, genetic testing, insulin discontinuation, glycemic control, cost-effectiveness
- MeSH terms
- Adolescent, Adult, C-Peptide, Diabetes Mellitus, Type 1, Diabetes Mellitus, Type 2, Humans, Biomarkers, Young Adult
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