Blood Glucose Threshold for Withholding Lantus (Insulin Glargine)
Lantus should be withheld when blood glucose is below 70 mg/dL (3.9 mmol/L), as this represents the clinical definition of hypoglycemia and administering insulin at this level significantly increases the risk of severe hypoglycemia with potentially life-threatening consequences. 1
Primary Threshold: 70 mg/dL (3.9 mmol/L)
The American Diabetes Association defines any blood glucose <70 mg/dL (3.9 mmol/L) as hypoglycemia, which is the critical threshold where counterregulatory hormone release begins. 1
This 70 mg/dL cutoff represents Level 1 hypoglycemia and serves as the "hypoglycemia alert value" requiring immediate therapeutic dose adjustment of all glucose-lowering medications, including basal insulin. 1
Administering Lantus when glucose is already <70 mg/dL substantially increases the risk of progression to Level 2 hypoglycemia (<54 mg/dL or 3.0 mmol/L), where neuroglycopenic symptoms including confusion, seizures, and loss of consciousness occur. 2, 1
Conservative Threshold for High-Risk Patients: 100 mg/dL (5.6 mmol/L)
For hospitalized patients, those with limited oral intake, or patients at high risk for hypoglycemia, consider withholding Lantus when blood glucose falls below 100 mg/dL (5.6 mmol/L) to provide an adequate safety margin. 2, 1
The 100 mg/dL threshold is specifically recommended for insulin regimen reassessment in hospitalized patients to prevent hypoglycemia. 1
High-risk populations requiring this more conservative threshold include: elderly patients (>65 years), those with renal impairment, hepatic disease, hypoglycemia unawareness, sepsis, acute illness, or poor oral intake. 2, 1
Clinical Algorithm for Lantus Administration
Before each Lantus dose, always check blood glucose—never rely on symptoms alone to determine hypoglycemia status. 1
If glucose <70 mg/dL (3.9 mmol/L):
- Hold the Lantus dose immediately. 1
- Treat hypoglycemia first with 15-20 g of fast-acting carbohydrate (preferably glucose). 2
- Recheck blood glucose in 15 minutes and repeat treatment if still <70 mg/dL. 2
- Once glucose returns to >70 mg/dL, provide a meal or snack to prevent recurrence. 2
- Reassess the insulin regimen before resuming Lantus—dose reduction is likely needed. 2
If glucose 70-100 mg/dL in high-risk patients:
- Hold the Lantus dose. 1
- Provide food first, then reassess the need for insulin. 1
- Consider reducing the Lantus dose by 20% when resuming therapy. 2
If glucose ≥100 mg/dL:
- Lantus may be administered as prescribed in most patients. 1
- Continue monitoring for hypoglycemia risk factors. 2
Critical Safety Considerations
Never administer Lantus when blood glucose is already in the hypoglycemic range (<70 mg/dL), as insulin glargine has a 24-hour duration of action and will continue lowering glucose. 2, 1
Severe hypoglycemia (Level 3) can cause permanent brain damage, seizures, coma, and death—the mortality risk increases substantially with more severe hypoglycemia. 2
Patients with hypoglycemia unawareness require higher glucose thresholds before insulin administration, as they lack the warning symptoms that prompt early intervention. 2, 1
In critically ill patients, hypoglycemia (<70 mg/dL) is independently associated with increased mortality (odds ratio 3.233), longer ICU stays, and greater hospital mortality, especially with recurrent episodes. 2
Common Pitfalls to Avoid
Do not assume a patient is not hypoglycemic based on lack of symptoms—always confirm with blood glucose measurement, as hypoglycemia unawareness is common. 1
Avoid overcorrecting hypoglycemia with excessive dextrose, which can lead to rebound hyperglycemia; use calculated doses (10-20 g for glucose <70 mg/dL). 2
Do not resume full-dose Lantus after a hypoglycemic episode without dose reduction—patients experiencing hypoglycemia require regimen reevaluation and typically need 20% dose reduction. 2
Be especially vigilant in patients with renal impairment, as reduced insulin clearance increases hypoglycemia risk even at standard doses. 2, 1