Discordance In Fasting And Postprandial Indices Of Glycemic Dysregulation In Individuals With Spinal Cord Injury

Abstract

Fasting levels of glucose and insulin are routine clinical measures used to diagnose type-2 diabetes. However, individuals with spinal cord injury (SCI) often present with clinically normal fasting glucose but have impaired postprandial responses to a meal challenge. PURPOSE: We aimed to characterize the postprandial glycemic responses and assess the prevalence of glycemic dysregulation using fasting and postprandial indices in individuals with SCI. METHODS: Sixteen men with chronic SCI reported to the laboratory after an overnight fast to undergo either a 2-hour: oral glucose tolerance test (OGTT) using a 75-g (~300 kcal) glucose load (n = 8) or; a mixed meal tolerance test (MMTT, (1037 ± 148 kcal: 45% CHO, 37% fat, 18% PRO) (n = 8). Serial measurements of systemic glucose and insulin concentrations at baseline and in response to the OGTT/MMTT were converted into summary statistics: Insulin Resistance was estimated by the Homeostasis Model Assessment of Insulin Resistance (HOMA2-IR); whole body Insulin Sensitivity Index was estimated using methods described by Matsuda (ISIMatsuda). RESULTS: There were no differences between groups in age (p = 1.0), body mass index (p = 0.87), cardiorespiratory fitness (p = 0.26), fasting glucose (p = 0.53) or insulin (p = 0.19). In the MMTT group, 3 (38%) individuals were identified as prediabetic (fasting plasma glucose (FPG), 7.3 ± 0.9 mmol/L) and 0 individuals had impaired insulin resistance (HOMA2-IR, 1.05 ± 0.6). However, 5 (63%) individuals had impaired postprandial insulin sensitivity (ISIMatsuida, 2.2 ± 0.4). In the OGTT group, 2 (25%) individuals were prediabetic (FPG, 6.2 ± 0.2 mmol/L), 2 (25%) different individuals had impaired insulin resistance (HOMA2-IR, 3.2 ± 0.9), but 7 (88%) individuals had impaired postprandial insulin sensitivity (ISIMatsuida, 2.3 ± 0.9). CONCLUSIONS: In this small study, an OGTT identified more SCI participants with glucose dysregulation than MMTT. Postprandial measures of insulin sensitivity identified a greater proportion of SCI participants with impaired glycemic control and may have preferred utility in identifying individuals at high risk of diabetes. Future studies should compare and contrast the specificity and sensitivity of fasting and postprandial methods in this high-risk population.