Endocrinology

Carbohydrate-to-Insulin Ratio

Calculates the grams of carbohydrates covered by 1 unit of insulin.

Parameters

Units

Carbohydrate-to-Insulin Ratio Result

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FormulaCIR = 500 / Total Daily Dose (TDD) of Insulin

Clinical Pearls

Empowers patients to adjust their mealtime (prandial) insulin bolus based precisely on what they plan to eat, rather than being locked into fixed doses.

Limitations

The "500 Rule" is an estimate. Individual patient insulin sensitivity varies, and the ratio may need fine-tuning. It only applies to rapid-acting insulins (e.g., Lispro, Aspart).