The goal of a threshold suspend device system is to help reduce the severity or reverse a dangerous drop in blood glucose level (hypoglycemia) by temporarily suspending insulin delivery when the glucose level falls to or approaches a low glucose threshold. These are sometimes referred to as “low glucose suspend systems.”
This kind of system serves as a potential back-up when a patient is unable to respond to a hypoglycemic event. Patients using this system will still need to be active partners in managing their blood glucose levels by periodically checking their blood glucose levels and by giving themselves insulin or eating.
A CTR system reduces the likelihood of a hypoglycemic event or a hyperglycemic event (when blood glucose is dangerously high) by adjusting insulin dosing only if a person’s glucose level approaches the low or high glucose thresholds. Patients using this system will still need to check blood glucose levels and give themselves insulin to maintain control of glucose levels.
A CTT system sets target glucose levels and tries to achieve these levels at all times. This system is fully automated and requires no interaction from the user (except for calibration of the continuous glucose monitoring system).
CTR and CTT System Subtypes are dependent upon the drug or drugs being delivered and how each drug affects glucose levels. Three subtypes are being investigated: insulin-only, bi-hormonal and hybrid:
An insulin-only system achieves a target glucose level by increasing or decreasing the amount of insulin infused.
A bi-hormonal control system achieves a target glucose level by using two algorithms to instruct an infusion pump to deliver two different hormones – one hormone (insulin) to lower glucose levels and another (such as glucagon) to increase blood glucose levels. The bi-hormonal system mimics the glucose-regulating function of a healthy pancreas more closely than an insulin-only system.
A hybrid system allows the patient to supplement insulin automatically prior to a meal. This pre-meal supplement decreases the risk of hyperglycemia after eating.