For temporary or sickness-related elevated blood sugar, a small dose of rapid-acting insulin is used for correction. If blood sugar is consistently elevated in the morning or before meals, it's advisable to identify the cause using a glucose sensor and adjust the baseline treatment – either the insulin for the preceding meal or the basal insulin, rather than repeatedly correcting the blood sugar with rapid-acting insulin.
Insulin sensitivity and the associated total daily insulin requirement influence the correction dose amount. With a typical total insulin amount of 40-50 units, 1 unit of rapid-acting insulin usually reduces blood sugar by about 2 mmol/l. For someone who is insulin-sensitive, 1 unit of rapid-acting insulin can reduce blood sugar by 4-5 mmol/l, and for someone insulin-resistant, 1 unit might only reduce it by 1 mmol/l. The following indicative 100-rule can be used to evaluate the correction dose of insulin.
Insulin Sensitivity Factor (ISF)
How much 1 unit of rapid-acting insulin reduces blood sugar:
Divide the number 100 by the total daily insulin (basal insulin + mealtime insulins) unit amount.
Examples:
For a person whose insulin requirement is a total of 50 units per day:
100 / 50 = 2
1 unit of rapid-acting insulin reduces blood sugar by about – 2 mmol/l.
For a person whose insulin need is a total of 30 units per day:
100/30 = 3.3
1 unit of rapid-acting insulin reduces blood sugar by about – 3 mmol/l.
Between meals, quick corrections should be made cautiously. Without a glucose sensor and/or dose calculator, it's hard to determine how much of the previous rapid-acting insulin is still active, and whether blood sugar is rising or falling.
Generally, rapid-acting insulin correction doses shouldn't be taken less than two hours after the previous injection. Even then, the correction dose should ideally be only half of the dose that would be taken before a meal. Otherwise, the effect of insulin easily accumulates, potentially resulting in a blood sugar rollercoaster.