Diabetes Care, Vol 20, Issue 2 198-201, Copyright © 1997 by American Diabetes Association
The classification of diabetes by clinical and C-peptide criteria. A prospective population-based study
FJ Service, RA Rizza, BR Zimmerman, PJ Dyck, PC O'Brien and LJ Melton
Division of Endocrinology and Metabolism, Mayo Clinic, Rochester, Minnesota 55905, USA.
OBJECTIVE: To evaluate both the concordance in the classification of
diabetes by clinical and C-peptide criteria and, prospectively, the
consistency of the classification by C-peptide. RESEARCH DESIGN AND
METHODS: Individuals with diabetes who were enlisted in the prospective
epidemiological study of diabetic neuropathy (Rochester Diabetic Neuropathy
Study [RDNS]) were classified clinically by National Diabetes Data Group
(NDDG) criteria to IDDM and NIDDM at entry to the study. In addition,
C-peptide response to 1 mg glucagon was measured at entry for the
classification to IDDM (basal C-peptide, < 0.17 pmol/ml; increment above
basal, < 0.07 pmol/ml) and NIDDM (all other responses) and for
concordance with the clinical classification made. The consistency of the
C-peptide response was assessed every 2 years for up to 8 years. RESULTS:
Among 346 individuals with diabetes, 84 were classified as IDDM and 262 as
NIDDM by clinical algorithm. COncordance with the C-peptide response
occurred in 89% of the patients and remained consistent during 8 years of
follow-up. Among the 37 patients with discordant clinical and C-peptide
classification, those considered clinically to have NIDDM had a consistent
IDDM C-peptide response during follow-up, and most of those considered to
have IDDM clinically eventually showed an IDDM C-peptide response during
follow-up. CONCLUSIONS: Clinical criteria for the classification of
diabetes are highly correlated with the assessment of insulin secretory
reserve. A small number of individuals considered to have NIDDM clinically
or by C-peptide have or develop an IDDM peptide response.