Introduced in the 1970s by Ralph A De Fronzo, Jordan Tobin, and Reubin Andres to quantify insulin secretion and resistance, glucose clamp studies are now considered the “gold standard” for studying pharmacodynamic and pharmacokinetics effects of different formulations of insulin. There are many variants of the glucose clamps such as the hyperinsulinemic-euglycemic, hypoglycemic, and hyperglycemic glucose clamps.
Hyperglycemic glucose clamps are used for quantifying the sensitivity of beta cells to glucose by maintaining a steady hyperglycemic state through infusion of variable concentrations of glucose. Hypoglycemic clamps have been used to study iatrogenic hypoglycemia and the effect of hypoglycemic agents on the hepatic glucose production while hyperinsulinemic-euglycemic clamps are used for their ability to detect subtle differences in insulin preparations.
For hyperinsulinemic-euglycemic pumps, the plasma insulin concentration is raised to a pre-determined level by priming and continuous infusion of insulin. In addition, the plasma glucose concentration is maintained by exogenous glucose infusion to induce a steady state of hyperglycemia. This helps in measuring the whole-body sensitivity to insulin wherein the concentration of infused exogenous glucose must be equal to the amount of glucose used by the body in response to the induced hyperglycemic state. Similarly, hyperglycemic pumps function by keeping a constant plasma glucose concentration with the desired hyperglycemic plateau and are helpful in assessing an individual’s insulin secretion capacity.
In hypoglycemic clamp studies, a pre-defined blood glucose concentration is maintained for a specified period by separate intravenous infusion of insulin and glucose. Blood samples are then collected at the glucose plateau phase for further biochemical study of counter regulatory hormonal responses. This may help in identifying any glycemic threshold that can be correlated to the onset of hypoglycemic symptoms.
Advantages of glucose clamps
- Reproducible results with accurate measurement of insulin action
- Hyperinsulinemic-euglycemic pumps are safe for use in elderly patients as well as in special population such as individuals with renal or hepatic disorders.
- Hypoglycemic clamp is the best method to understand and study counter-reactions to hypoglycemic conditions.
- The perfect apparatus for assessing preparations of insulin or insulin analogs
- Clamp studies do not interfere with the results of other test techniques and can be used in combination with them. For example, determination of hepatic function.
To validate the outcome of glucose clamp studies, it is necessary to ensure good quality of glucose clamps along with improved computer algorithms to obtain optimal glucose infusion rates and sound blood glucose data. Eventually, such standardized results will be beneficial in research studies on diabetes and its management.