Glucose tolerance and insulin sensitivity are important measures when detecting and diagnosing metabolic diseases like type 2 diabetes. They can also independently predict cardiovascular disease and mortality. An oral glucose tolerance test (OGTT) can be used to quantify glucose tolerance and insulin sensitivity in vivo and is used frequently in clinical diagnostics and research settings to evaluate the effect exercise or diet has on blood glucose levels.
The OGTT involves an overnight fast, followed by ingestion of 75g of glucose and then an observation period (typically 120 minutes) where blood samples are taken to determine blood glucose concentrations. When combined with insulin measurements, it is possible to estimate whole-body insulin sensitivity. However, a limitation associated with the OGTT is the guidelines provide no clear consensus or justification for the best blood sampling technique, consequently resulting in the use of many different techniques.
Previously, no studies had been performed to directly compare arterialized and venous blood samples under different metabolic conditions to estimate glucose tolerance and OGTT-derived insulin sensitivity. To fill this gap in knowledge, a recent study conducted by Gonzalez and colleagues aimed to investigate the impact of prior exercise on glucose levels and insulin sensitivity measured by various blood sample methods. The results were published recently in the British Journal of Nutrition.
The study included 10 healthy, physically active men with an average age of 23 and no prior history of metabolic disease or conditions.Participants underwent an overnight 10 hour fast and refrained from any strenuous physical activity and caffeine intake for 24 hours. They were asked to record their evening meal and any physical activity from the day before. This was repeated for their second visit, in line with standard procedures for glucose tolerance testing.Each participant completed two trials in random order.
For the“rest” trial, samples were taken while participants were at rest and lying down, and for the “exercise” trial, 60 minutes of cycling was completed prior to samples being taken. Blood samples were taken simultaneously from the subject’s dominant hand which was heated (arterialised) and an inner forearm vein of the opposite arm (venous).
The results showed that at baseline there was no difference in glucose levels between arterialized and venous blood in either the rest or exercise trials. However, arterialised blood showed higher glucose concentration compared with venous blood and the difference was larger after in resting measurements.
Furthermore, when compared to arterialized blood, venous blood samples produced different values, with lower glucose concentrations after glucose was ingested and higher insulin sensitivity estimates. When whole-body glucose tolerance was evaluated, inconsistencies were observed between the sampling methods under the different metabolic conditions. Therefore, due to the differences observed in oral glucose tolerance between methods and metabolic conditions, this study highlighted not only the difficulty in being able to standardize these tests to compare between arterialized and venous blood samples, but also the method used for sampling blood is an important consideration. It was noted by the authors that establishing the underlying mechanism for why there was a larger arterialized to venous difference after rest compared to after exercise is beyond the scope of this study.
Given glycemia is an important indicator used for predicting the potential risk of diseases such as type 2 diabetes, it is essential to note the blood sampling technique and metabolic condition prior to testing. Accounting for these differences has the potential to improve the accuracy of detection and diagnosis.
Written by Lacey Hizartzidis, PhD
Reference: Edinburgh RM, Hengist A, Smith HA, Betts JA, Thompson D, Walhin JP, Gonzalez, JT. Prior exercise alters the difference between arterialised and venousglycaemia: implications for blood sampling procedures. Br J Nutr. 2017 Jun15:1-8. doi: 10.1017/S0007114517001362.
Edinburgh RM, Hengist A, Smith HA, Betts JA, Thompson D, Walhin JP, Gonzalez, JT. Prior exercise alters the difference between arterialised and venous glycaemia: implications for blood sampling procedures. Br J Nutr. 2017 Jun15:1-8. doi: 10.1017/S0007114517001362.