C-peptide in NIDDM. Follow-up for 4-6 yr

To study whether fasting and 1-h postbreakfast C-peptide levels in NIDDM stabilize with time in individual patients.

Within the period of 4-6 yr, 49 NIDDM patients had repeated tests of fasting and 1-h postprandial levels of plasma glucose and C-peptide with the aim of determining their individual qualitative patterns. Throughout the follow-up period, 13 patients were treated with insulin, 21 with oral sulfonylureas, and 15 were switched from oral drugs to insulin, with the tests done in both treatment periods.

The group as a whole demonstrated no changes in mean fasting or postprandial C-peptide within 4-6 yr of observation, irrespective of the mode of therapy or its changes. Glycemic and C-peptide response to breakfast was qualitatively typical for each patient with the correlation between plasma glucose and C-peptide. However, the response was vastly different from patient to patient, and the cross-sectional data showed no correlation between postprandial changes in glycemia and C-peptide, nor between glycemic response to breakfast and fasting plasma glucose or C-peptide. In spite of high fasting glycemia, 25% of the patients showed remarkable tolerance to breakfast with only small increases in plasma glucose. In many other patients, however, in spite of similar increase in C-peptide, plasma glucose rose sharply after the meal.

In our group, no deterioration of the insulin secretory function was observed within 4-6 yr of follow-up. Qualitative patterns of the glycemic and C-peptide responses to breakfast were typical for each patient but vastly different between patients. We see in NIDDM a syndrome with few common characteristics and recommend further work for its subclassification into forms with different pathogenesis.