Sliding-scale insulin therapy bases the amount of insulin a diabetic needs to take prior to eating on the pre-meal blood sugar. The higher the blood sugar, the more insulin required. Sliding-scale therapy has been used since the 1930s and is common in hospitals and other health care facilities.
This sliding-scale method requires that the amount of carbohydrates consumed at each meal remain fixed. Carbohydrate sources may change, but the actual amount consumed at a particular meal must remain unchanged. The amount of long-acting, or background, insulin also remains fixed. Only the bolus and pre-mixed insulin doses change depending on pre-meal blood sugar.
This method has fallen into disfavor because it doesn't seem to control blood sugar very well. It can cause patients to have blood sugar highs and lows, and it cannot be personalized according to meal contents, activity or stress levels. Furthermore, it bases the current insulin dose on how well the last dose worked, not on what actually is needed for a given meal.
Alternatives to sliding-scale insulin therapy include fixed-dose insulin therapy and the carbohydrate-to-insulin ratio. In fixed-dose therapy, the number of insulin units given at each meal remains the same, regardless of blood sugar and meal content. While this is an easy system to learn, it lacks personalization regarding meal contents and activity. In contrast, the carbohydrate-to-insulin ratio tailors the amount of insulin given to the amount of carbohydrates in a meal.