Goal of Long-Acting Insulin for Fasting Blood Glucose in the Morning
The target fasting blood glucose level for patients using long-acting insulin should be 90-150 mg/dL (5.0-8.3 mmol/L), as this range balances effective glycemic control with minimized risk of hypoglycemia. 1
Rationale for Target Range
- Long-acting (basal) insulin's primary purpose is to restrain hepatic glucose production and limit hyperglycemia overnight and between meals 1
- The appropriateness of the insulin dose for patients using a bedtime long-acting insulin regimen is best defined by the fasting/pre-breakfast blood glucose test 1
- For most patients, a fasting blood glucose concentration of 70-130 mg/dL is a reasonable target, though this may be difficult to achieve in some populations 1
- For older adults, guidelines specifically recommend a slightly wider target range of 90-150 mg/dL to reduce hypoglycemia risk while maintaining adequate control 1
Monitoring and Dose Adjustment
- For patients on a single bedtime long-acting insulin regimen, daily fasting blood glucose measurements are recommended 1
- Dose adjustments should be based on fasting fingerstick glucose test results over a week 1
- If 50% of the fasting fingerstick glucose values are over the goal, increase the dose by 2 units 1
- If more than 2 fasting fingerstick values per week are below 80 mg/dL, decrease the dose by 2 units to prevent hypoglycemia 1
Clinical Significance
- Achieving target fasting glucose levels is essential for overall glycemic control, as a drop in fasting blood glucose of 28.7 mg/dL correlates with approximately a 1% drop in HbA1c 2
- Long-acting insulin analogs (glargine, detemir, degludec) have been demonstrated to reduce the risk of nocturnal hypoglycemia compared with NPH insulin 1, 3, 4
- Studies show that patients reaching target fasting blood glucose with basal insulin can achieve HbA1c levels around 7.6-7.7% 3
- Long-acting insulin analogs provide smoother glucose control with less increase in glucose levels during the last 4 hours of the 24-hour injection interval 5, 6
Common Pitfalls and Considerations
- Overbasalization: Using excessive basal insulin doses (>0.5 units/kg) can lead to nocturnal hypoglycemia without adequately controlling daytime glucose 1
- Timing considerations: Some patients may benefit from changing basal insulin timing from bedtime to morning to optimize the insulin action profile 1
- Hypoglycemia risk: This regimen is associated with some risk of overnight or fasting hypoglycemia, requiring careful monitoring 1
- Inadequate mealtime coverage: Patients may have fasting blood glucose in target but daytime readings above target, indicating a need for additional mealtime insulin or other agents 1
Special Populations
- For older adults, simplification of insulin regimens may be necessary, with a focus on maintaining the 90-150 mg/dL fasting target while minimizing hypoglycemia risk 1
- In hospitalized patients, the fasting glucose target may be adjusted to 80-180 mg/dL to balance control with safety in the acute setting 1
- For patients on glucocorticoid therapy, basal insulin requirements may increase significantly, and dose adjustments should be more frequent 1