Correction Insulin

Correction insulin is a dose of rapid-acting insulin added to a mealtime dose, or given alone, to bring a raised glucose back to target. It is used with basal or basal bolus insulin, in hospital and at home. It should never be the only insulin in a patient who needs basal cover, because sliding-scale-only regimens give poor control and swings between high and low glucose.

Insulin sensitivity factor. The fall in glucose caused by 1 unit of rapid-acting insulin. It is estimated as 100 divided by the total daily dose of insulin, in mmol/L. Most adults fall by 2 to 3 mmol/L for each unit.

Time window. Rapid-acting insulin acts for 3 to 5 hours, so correction doses given too close together stack and cause hypoglycaemia.

Insulin. A rapid-acting analogue (aspart, lispro, glulisine) given 0 to 15 minutes before a meal. Human soluble insulin acts slower and is given 30 minutes before eating; it needs more caution when used for correction.

Where correction is used. Type 1 diabetes, type 2 diabetes on basal bolus insulin, and hospital inpatients with glucose persistently over target.

Not for. Diabetic ketoacidosis and hyperosmolar states, which need an intravenous infusion.

Formula. Correction dose in units equals (current glucose minus target glucose) divided by the insulin sensitivity factor. A common target is 7 mmol/L at home and 6 to 10 mmol/L in hospital.

Fixed hospital correction scales (units of rapid-acting insulin before meals).

Bedtime. Give 50% of the calculated correction and only if glucose is over 14 mmol/L, because nocturnal hypoglycaemia risk is highest.

Between meals. Avoid correction within 3 to 4 hours of the last rapid-acting dose.

Review the scale. If correction is needed on 3 consecutive days at the same time, increase the basal or mealtime insulin and not the correction.

Special groups. - Kidney impairment: use the sensitive scale and reduce doses by 25% at eGFR 10 to 50. - Liver disease: use the sensitive scale; avoid corrections over 4 units in decompensated cirrhosis. - Pregnancy: tighter targets and specialist-set correction factors. - Older adults: use the sensitive scale and wider targets. - Steroid therapy: use the resistant scale in the afternoon and evening, and reduce as steroids fall. - Children: use weight-based factors set by a paediatric diabetes team.

Monitoring. Capillary glucose before meals and at bedtime, plus 03:00 if hypoglycaemia occurs. Record every correction dose.

Stopping. Stop correction when intake is poor, when glucose is under 7 mmol/L, or when the patient is unwell with vomiting and cannot eat.

Referral and escalation. Refer for glucose persistently over 20 mmol/L, any glucose under 4 mmol/L after correction, ketones of 1.5 mmol/L or more, or the need for repeated large corrections.