Ideal Fasting Blood Glucose Target for Basal Insulin Therapy
The ideal fasting blood glucose target when on basal insulin is 90-150 mg/dL (5.0-8.3 mmol/L), as recommended by the American Diabetes Association. 1, 2
Target Range and Rationale
The 90-150 mg/dL (5.0-8.3 mmol/L) fasting glucose target represents the standard goal for patients on basal insulin therapy across multiple diabetes care guidelines. 1, 2
This target range balances glycemic control with hypoglycemia prevention, which is critical since basal insulin action peaks during the early morning hours (midnight to 6:00 AM) when hypoglycemia risk is highest. 1
The target may be adjusted based on overall health status, goals of care, and individual patient factors, but the default starting point should be this 90-150 mg/dL range. 1
Titration Strategy Based on Fasting Glucose
When titrating basal insulin, use the following algorithm:
If 50% or more of fasting glucose values over one week exceed 150 mg/dL: Increase basal insulin dose by 2 units. 1
If more than 2 fasting glucose values per week fall below 80 mg/dL (4.4 mmol/L): Decrease basal insulin dose by 2 units. 1
Monitor fasting fingerstick glucose results over a one-week period before making dose adjustments. 1
Important Considerations About Morning Fasting Glucose
A critical caveat: The morning fasting glucose can be misleading if patients consume late or large evening meals, which artificially elevate the fasting value and may lead to excessive basal insulin dosing. 3
This phenomenon is particularly common in obese patients with type 2 diabetes and can contribute to hypoglycemia and weight gain. 3
During basal insulin titration, evening meals should be limited and hypoglycemia should be monitored in the early morning hours (the "bewitching time" when basal insulin action peaks). 3
Timing of Basal Insulin Administration
Basal insulin should be administered at the same time each day. 2
Morning administration of basal insulin reduces nocturnal hypoglycemia risk compared to bedtime dosing, while achieving equivalent glycemic control. 2, 4
The choice between morning or bedtime administration can be flexible based on patient preference, as both achieve similar fasting glucose control. 4
Verification of Basal Insulin Adequacy
To confirm appropriate basal insulin dosing, blood glucose should remain stable during fasting:
In ideal conditions, blood glucose concentrations should increase or decrease by no more than 1.7 mmol/L (approximately 30 mg/dL) during fasting periods. 1
This stability indicates that basal insulin rates are appropriately matched to hepatic glucose production. 1
For patients on insulin pumps, 24-hour fasting tests can reveal circadian variations in basal insulin requirements, with peaks typically occurring during the "dawn" period (1:00-7:00 AM). 5
Safety Considerations
Never use rapid- or short-acting insulin at bedtime to avoid nocturnal hypoglycemia. 1, 2
The target fasting glucose of 80-180 mg/dL (4.4-10.0 mmol/L) is recommended in perioperative settings, representing a slightly wider safety margin. 1
Previous episodes of hypoglycemia significantly increase the risk of subsequent hypoglycemic events, so any fasting glucose below 80 mg/dL should prompt immediate dose reduction. 1