Should You Check Bedtime Glucose?
Yes, you should check your blood glucose at bedtime, especially if you are on insulin therapy, as bedtime glucose levels help identify risk for nocturnal hypoglycemia, though they are imperfect predictors and additional strategies may be needed.
Who Should Check Bedtime Glucose
Insulin-Treated Patients (Highest Priority)
- All patients on insulin therapy should test blood glucose at bedtime 1.
- Patients using intensive insulin regimens (multiple daily injections or insulin pumps) require bedtime testing as part of their 6-10 daily glucose checks 1.
- Those on basal insulin (such as bedtime long-acting insulin) should perform daily fasting measurements, but bedtime testing remains important for detecting hypoglycemia risk 1.
High-Risk Populations Requiring Bedtime Testing
- Younger patients with type 1 diabetes have higher risk of nocturnal hypoglycemia and require bedtime monitoring 2.
- Patients with HbA1c <7% face increased nocturnal hypoglycemia risk 2.
- Elderly patients or those with strict glycemic control targets should test at bedtime due to increased hypoglycemia risk 1.
- Patients with hypoglycemia unawareness must test bedtime glucose to prevent severe nocturnal episodes 1.
Why Bedtime Testing Matters Despite Limitations
The Nocturnal Hypoglycemia Problem
- Approximately 50% of all severe hypoglycemia episodes occur during sleep 3.
- Nocturnal hypoglycemia affects 25-33% of insulin-treated patients on any given night 2, 4.
- Bedtime glucose levels are poor predictors of nocturnal hypoglycemia 1, but they remain the best readily available tool for risk assessment.
Clinical Consequences of Missed Nocturnal Hypoglycemia
- Nocturnal hypoglycemia can cause seizures, coma, cardiac arrhythmias, and has been implicated in "dead-in-bed syndrome" 3.
- Recurrent nocturnal hypoglycemia impairs awareness of future hypoglycemic episodes, creating a dangerous cycle 1, 3.
- Morning symptoms include nightmares, restless sleep, low fasting glucose, headache, confusion, or behavior changes 1.
Actionable Bedtime Glucose Thresholds
When to Intervene Based on Bedtime Values
- If bedtime glucose is ≤100 mg/dL (5.6 mmol/L), consume a small snack 1.
- If bedtime glucose is ≤9 mmol/L (162 mg/dL), consider additional bedtime snack to reduce nocturnal hypoglycemia risk by approximately 44% 4.
- Bedtime glucose <70 mg/dL (3.9 mmol/L) requires immediate treatment with 15g carbohydrate 1.
Additional Risk Factors to Consider at Bedtime
- Medium or high-intensity exercise during the day significantly increases nocturnal hypoglycemia risk 2.
- Daytime hypoglycemia predicts higher likelihood of nocturnal hypoglycemia 2.
- Lower HbA1c levels correlate with increased nocturnal hypoglycemia frequency 2.
Testing Frequency for Non-Insulin Users
Type 2 Diabetes on Oral Agents Alone
- Once treatment goals are met with oral agents that have low hypoglycemia risk, bedtime testing can be infrequent or intermittent 1.
- Resume more frequent bedtime testing during illness, with symptoms of hypoglycemia, or when treatment changes 1.
Type 2 Diabetes on Basal Insulin Plus Oral Agents
- Bedtime testing should continue regularly until metabolic control is established 1.
- After achieving stable control, frequency can be reduced but should not be eliminated entirely 1.
Common Pitfalls and How to Avoid Them
The Bedtime Snack Misconception
- Conventional bedtime snacks do NOT reliably prevent nocturnal hypoglycemia 5.
- Uncooked cornstarch bars also failed to prevent nocturnal hypoglycemia in controlled studies 5.
- Bedtime snacks should be used as an adjunct to, not replacement for, appropriate insulin dosing 3.
Relying Solely on Bedtime Values
- Since bedtime glucose poorly predicts nocturnal hypoglycemia 1, consider middle-of-night testing (2-4 AM) if symptoms suggest nocturnal lows 1.
- Patients with unexplained high fasting glucose despite controlled daytime values should test during the night to detect nocturnal hypoglycemia 1.
Insulin Pump Users
- Pump users require especially vigilant bedtime testing because interrupted insulin delivery can rapidly lead to ketoacidosis 1.
- These patients need frequent monitoring both to guide bolus dosing and to detect delivery failures 1.
Special Circumstances Requiring Bedtime Testing
During Treatment Adjustments
- Any change in insulin regimen mandates increased bedtime testing 1.
- When switching between insulin types (e.g., to long-acting analogs), bedtime testing helps identify timing and dosing needs 6.
Pregnancy
- Pregnant patients with type 1 diabetes require postprandial and bedtime testing to approach euglycemia for fetal benefit 1.