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.
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.
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), i.e. £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).
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.