Usefulness of oral glucose tolerance test (OGTT) in outpatients with advanced chronic renal failure (CRF)

A pathological Oral Glucose Tolerance test (OGTT) is an early marker of peripheral insulin resistance. Nevertheless, its utility in nondiabetic patients with CRF stage IV-V is undetermined. Aim: We wanted to detect, in a population of non diabetic patients with CRF, the presence of carbohydrates metabolism anomalies, by means of the OGTT and to relate it with metabolic, anthropometric, cardiovascular parameters and renal function. We studied 45 non diabetic patients with advanced CRF (stage IV-V), 26 men, mean age 66.5 years, with average Cockroft-Gault of 23.6 ml/min. We measured weight, height, waist and BMI. Biochemical: glucose, insulin, OGTT, C peptide, lipid profile, HbA1C and Hto. Cardiovascular comorbidity, mean proteinuria and systolic and diastolic blood pressure (6 months pre and post analytical measure) were measured. Pulse pressure was also calculated. Results: 47% of the patients presented normal fasting glucose, whereas 53% had isolated impaired fasting glucose (IFG). After the OGTT, 36% of the patients presented impaired glucose tolerance (IGT) and 14% diabetes (> 200 mgldl). Of the patients with normal fasting glucose, 38% had /CT after OGTT and 5% diabetes. Patients with IFG (n = 24), 33% presented IGT and 21 % diabetes. Patients with abnormal OGTT were older (71 +/- 13.6 versus 60 +/- 18.8 years, p = 0.03), had greater HbA1C (5.6 +/- 0.5 versus 5.2 +/- 0.3%, p = 0.02), total cholesterol (193 +/- 37.7 versus 169.8 +/- 44.9 mg/dl, p = 0.03), pulse pressure (63.4 +/- 14.5 versus 52.3 +/- 9.7 mmHg, p = 0.0001) and greater prevalence of ischemic heart disesase (28% versus 5%, p = 0.05). Creatinine Clerance negatively correlated with the OGTT (r = -0.39, p = 0.01) and plasma creatinine positively with fasting insulin (r = 0.33, p = 0.02) and C-peptide (r = 0.42, p = 0.006). Urinary Proteins were correlated with fasting glucose (r = 0.30, p = 0.04), C-peptide (r = 0.52, p = 0.001), triglycerides (r = 0.36, p = 0.01) and with the HOMA-IR index (r = 0.30 p = 0.05) Conclusion: Fasting Glucose did not predict OGTT results in patients with CRF For this reason, we think that the OGTT can be very useful tool to identify states of ''prediabetes'' and diabetes in patients with CRF, specially in those whose present an elevated Pulse Pressure, age greater than 65 years, hyperlipidaemia and HbA 1 C above 5.2%. The early detection of these metabolic anomalies, may lead to intensify dietetic and pharmacological measures directed to delay or to attenuate the appearance of diabetes and its serious complications in a population in which the cardiovascular risks factors are very elevated.