At what glucose level should I intervene with insulin therapy at 10 pm and should I use NPH (Neutral Protamine Hagedorn) insulin or regular insulin?

Bedtime Glucose Monitoring and Insulin Intervention

You should intervene with insulin therapy if the glucose level at 10 PM is ≥180 mg/dL on two consecutive checks, and you should use regular insulin (not NPH) for this acute correction.

Intervention Threshold

Initiate insulin therapy when blood glucose is persistently ≥180 mg/dL (10.0 mmol/L), confirmed on two occasions within 24 hours. 1 This threshold applies to both critically ill and non-critically ill hospitalized patients and represents the consensus across the most recent American Diabetes Association and Society of Critical Care Medicine guidelines.

• The 180 mg/dL threshold is deliberately set lower than the target range to prevent prolonged periods of hyperglycemia 1
• A single elevated reading at 10 PM should prompt a repeat check within 1-4 hours to confirm persistent hyperglycemia before initiating therapy 1
• For patients already on insulin therapy, the target range should be 140-180 mg/dL (7.8-10.0 mmol/L) 1

Choice of Insulin: Regular vs NPH

Use regular insulin for acute correction at 10 PM, not NPH insulin. 1, 2

Why Regular Insulin is Preferred:

• Regular insulin acts within 30 minutes to 1 hour and peaks at 2-4 hours, making it appropriate for correcting elevated bedtime glucose levels 1
• Regular insulin should be administered every 6 hours for correctional purposes in hospitalized patients 1
• This allows for reassessment before the next scheduled dose and reduces overnight hypoglycemia risk

Why NPH is NOT Appropriate for 10 PM Correction:

• NPH insulin peaks at 4-6 hours after administration, which would occur at 2-4 AM, significantly increasing the risk of nocturnal hypoglycemia 1, 3
• NPH is an intermediate-acting insulin designed for basal coverage, not acute correction 1
• NPH is appropriate when given with morning glucocorticoids or for continuous enteral feeding coverage, but not for isolated bedtime hyperglycemia correction 1, 3

Practical Algorithm for 10 PM Management

Step 1: Check glucose at 10 PM

• If <180 mg/dL: No intervention needed; continue routine monitoring 1
• If ≥180 mg/dL: Proceed to Step 2

Step 2: Confirm persistent hyperglycemia

• Recheck glucose within 1-4 hours if this is the first elevated reading 1
• If both readings ≥180 mg/dL: Proceed to Step 3

Step 3: Administer regular insulin subcutaneously

• Use a correctional insulin scale (typically 1-4 units for glucose 180-250 mg/dL, adjusted based on insulin sensitivity) 1
• For critically ill patients, consider continuous IV insulin infusion instead 2, 4

Step 4: Recheck glucose in 4-6 hours

• Monitor for response and hypoglycemia risk 1
• Adjust subsequent doses based on response

Critical Pitfalls to Avoid

• Never use NPH insulin for isolated bedtime correction due to the high risk of nocturnal hypoglycemia occurring at 2-4 AM 1, 3
• Do not intervene based on a single glucose reading unless the patient is symptomatic or critically ill; confirm persistent hyperglycemia first 1
• Avoid targeting glucose <140 mg/dL at night as this significantly increases hypoglycemia risk without proven benefit 1, 5
• Do not use sliding scale insulin alone as the only management strategy; this should be part of a comprehensive basal-bolus regimen for patients with ongoing hyperglycemia 1, 2, 4

Special Considerations

• In patients receiving continuous enteral nutrition, NPH every 6-8 hours may be appropriate as part of the overall regimen, but regular insulin should still be used for acute corrections 1, 3
• For patients on glucocorticoid therapy, the hyperglycemia pattern typically improves overnight, making aggressive bedtime correction with NPH particularly dangerous 1
• Critically ill patients should have continuous IV insulin infusion rather than subcutaneous injections for better glycemic control 2, 4, 6