Variations in glucose/C-peptide ratio in patients with type 2 diabetes associated with renal function

Accurate dosing of medications for glycemic control is a challenge for clinicians in diabetic patients with kidney disease. Diminishing glomerular filtration rates are associated with decreased renal clearance of insulin and increased prevalence of hypoglycemic episodes. Measurement of glucose/C peptide ratios may be useful to guide dosing in those patients who receive powerful insulin secretogogues as glomerular function decreases with age and disease.

In order to determine the relationship between glucose, C-peptide and renal function, we reviewed the records of patients with type 2 diabetes followed in our kidney hypertension clinic who met the following criteria: age 35-90 years, requirement of medications to control glycemia, at least 4 simultaneous measurements of C peptide, HbA1c, creatinine and blood glucose.

87 patients (67 males, 20 females), ages 67.1 ± 10.6 years, BMI 32.5 ± 5.2, A1c 8.2 ± 1.2%, eGFR 73 ± 27.2 ml/min, had glucose/C-peptide ratios 60.7 ± 46.4. 59% of the total group were taking insulin secretogogues. Patients were divided into groups based upon mean eGFR and use or absence of insulin secretogogues. Glucose C-peptide ratios were lowest in the quartile of patients with the lowest eGFR (<50 ml/min).

Diminished renal function and advanced age are associated with the lowest glucose/C-peptide ratios, independent of achieved glycemic control. With similar use of secretogogues, glucose/C-peptide ratio were lower when eGFR was ≤49 ml/min compared to >50-80 ml/min. Use of secretogogues was associated with decreased glucose/C-peptide levels. In patients with reduced renal function (eGFR < 50 ml/min), use of insulin secretogogues may be associated with lower glucose/C-peptide ratios associated with higher risks for hypoglycemic reactions.