The sliding scale is one way of working out how much insulin to take before each meal. Doctors developed it several decades ago as a guide to insulin dosage, but few healthcare professionals now use it.
The American Diabetes Association (ADA) warn that using only sliding scale insulin for treatment is ineffective for most people. It can increase the risk of both high and low blood sugar and of complications if the person needs surgery.
Most doctors advise against using this approach.
As long ago as 2001, the author of an article published in Diabetes Care described the sliding scale as "arbitrary," and a "historical artifact."
How the sliding scale works
Sliding scale insulin therapy involves creating and following an individual chart.
The sliding scale is a chart of insulin dosages.
A doctor creates this chart with the individual. They base it on how the person's body responds to insulin, their daily activity, and a carbohydrate intake that they will agree on.
Insulin dosage will vary, depending on two factors:
Pre-meal blood glucose level: This usually appears on the left-hand side on the chart, from low to high, with higher doses of insulin toward the bottom of the chart. The more blood sugar a person has, the more insulin they will need to deal with it.
Mealtime: This usually appears along the chart's top row. This row will show breakfast, then lunch, then dinner.
Throughout the day, the dose will change. This is because insulin sensitivity — the way the body responds to insulin — can change as the day progresses.
The composition of meals can also change through the day, and the doctor may take that into consideration.
Reading the chart
To work out the right dosage using a sliding scale, people should follow these steps:
1. Test their blood glucose level.
2. Find the matching blood glucose value along the chart's left-hand column.
3. Slide horizontally along that value's row until they reach the current meal.
4. Take a dosage that matches the number where the two values meet.
The person should test their blood sugar levels before mealtimes, depending on the type of insulin they use.
Different types of insulin work over different periods of time. If a person uses a rapid-acting insulin, they may need to take their insulin 15–30 minutes before a meal.
Along with these mealtime rapid-acting doses, people often take a long-acting insulin dose once or twice a day.
The aim of this is to set a stable baseline blood glucose level for the body to work around.
Blood glucose monitors are available for purchase online.
Benefits and disadvantages
The sliding scale method requires very few daily calculations. People with diabetes may feel more comfortable following a pre-determined plan. However, these factors also make sliding scale treatment very inflexible.
The sliding scale needs a regimented diet and exercise program to succeed.
Carbohydrates: The person must consume the same number of carbs with each meal because the chart's calculations depend on a single carb value. This number should not change from day to day.
Meal timing: The person needs to eat their meals around the same time each day. If not, their insulin sensitivity may not match the ones the chart uses to work out the dosage for a specific meal.
Exercise: People should not vary the amount that they exercise much from day to day. Changes in activity and stress also affect blood glucose levels in a way that the sliding scale cannot account for.
However, it is difficult for most people to follow these meal and activity restrictions completely because the scale does not allow for changes in carb intake, the timing of meals, and exercise.
As a result, large changes in blood glucose levels can happen throughout the day.
Medical professionals also worry that the sliding scale poses a risk of continuous high blood glucose levels.
High blood sugar
A meta-analysis published in 2015 found that the use of the sliding scale did not improve glucose control, but it did lead to more frequent high blood sugar, or hyperglycemia.
Low blood sugar
The doses that a sliding scale chart requires might also be excessive if a person skips meals or is more sensitive to insulin on a given day.
As these doses build up throughout the day, they could lead to a dangerous drop in blood glucose levels. This can rapidly become a life-threatening emergency, leading to coma and possibly death.
High blood glucose levels increase the risk of complications during and after general surgery.
In 2018, authors of a report published in Anesthesiology noted that, "use of a sliding scale insulin alone is not acceptable as the single regimen in patients" around the time of surgery, as it can lead to high or low blood sugar levels. This can result in further complications.
In place of the sliding scale model, the ADA recommend other ways of taking insulin.
Conventional insulin therapy
This treatment involves injections of the following:
Short-term insulin: The person takes 2–3 doses of insulin each day, and they must co-ordinate their meals with the injections' peak activity times. The doses are the same each day and do not depend on pre-meal blood glucose levels.
Long-acting insulin: One dose each day. For this method to be effective, the person must take their meals at the same time each day, or unwanted fluctuations in blood glucose may result.
Alternatively, the person may use an insulin pen to inject insulin. The pens are adjustable, to allow for different doses.
The pen is easier to use than a syringe. It comes as a prefilled or refillable device.
Find out more about insulin pens in our dedicated article here.
Intensive insulin therapy
Intensive insulin therapy involves three types of insulin dose.
Another name for this method is basal-bolus therapy, or tight control.
The person must make daily calculations to keep their glucose levels as close to their target level as they can.
Intensive insulin therapy compensates in real-time for factors that may affect blood glucose levels and insulin sensitivity.
There are three main parts to an intensive insulin plan:
Basal insulin: This is a long-acting insulin that a person takes once or twice a day.
Nutritional insulin: This is a mealtime dose, which the person calculates according to the number of carbohydrates the meal will contain. To calculate the dose, the person should divide the number of grams of carb in the meal by the grams of carbs that one unit of insulin breaks down.
Correctional insulin: To form a complete mealtime dose, the person will need to combine a correctional insulin value with the nutritional insulin value. This may be necessary if a person has high blood glucose levels before a meal.
To calculate this dose, the person will work out the difference between their target glucose level and their current level, in other words, how much extra glucose is currently present. Then, they will take enough insulin to process the excess glucose.
A correction dose can also redress the insulin balance if a person does extra exercise or any other factors that might increase the sensitivity of or need for insulin.
Intensive insulin therapy is effective if a person follows it correctly, but it can be hard to use.
Insulin pump therapy
Many people who need insulin now use an insulin pump. It works on a similar principle to basal-bolus insulin, but it removes the need for regular injections.
The pump is a small, digital device that provides a steady supply of insulin throughout the day (basal), with an extra dose around mealtimes (bolus).
The person will wear the pump on their body. The insulin travels from the pump, through a small tube and needle, into the body.
The individual will need to work with their doctor to program the pump and to work out which doses they need. They may still need to inject insulin at mealtimes or after exercising.
They will also still need to check blood glucose levels regularly, as with other methods of insulin therapy.
Good blood sugar control can prevent complications from developing, and can help people to live a healthier and longer life.
Doctors no longer recommend using a sliding scale, but there are several other options to choose from.