The classification of diabetes by clinical and C-peptide criteria. A prospective population-based study.
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.


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.
Service
F J
FJ
Division of Endocrinology and Metabolism, Mayo Clinic, Rochester, Minnesota 55905, USA.
Rizza
R A
RA
Zimmerman
B R
BR
Dyck
P J
PJ
O'Brien
P C
PC
Melton
L J
LJ
D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000465:Algorithms; D015415:Biomarkers / Q000097:blood; D002096:C-Peptide / Q000097:blood* / Q000187:drug effects; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003920:Diabetes Mellitus / Q000097:blood / Q000145:classification / Q000175:diagnosis*; D005260:Female; D005500:Follow-Up Studies; D005934:Glucagon / Q000008:administration & dosage / Q000494:pharmacology; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies
D015415:Biomarkers; D002096:C-Peptide; D005934:Glucagon