Insulin therapy is essential for managing diabetes and regulating blood sugar levels, but this powerful tool requires careful use. While insulin is necessary for preventing hyperglycemia, or high blood sugar, knowing when to withhold a dose is equally important for patient safety. The primary danger of an incorrect insulin dose is hypoglycemia, a dangerously low blood sugar level. Understanding the specific threshold at which insulin should be avoided prevents serious health complications, including confusion, loss of consciousness, and seizures. This decision-making process depends on recognizing the low blood sugar boundary and understanding how other factors can increase the risk of a rapid drop.
Defining the Critical Blood Sugar Threshold for Avoiding Insulin
The universally recognized threshold for hypoglycemia in individuals with diabetes is a blood glucose reading below 70 milligrams per deciliter (mg/dL), which is equivalent to 3.9 millimoles per liter (mmol/L). This measurement is defined as the level at which the body’s counter-regulatory hormones, such as glucagon, begin to activate to raise glucose levels. When blood sugar falls to this point or lower, administering any additional insulin, especially a correctional dose, will accelerate the drop and can lead to severe hypoglycemia.
Mild to moderate hypoglycemia begins at 70 mg/dL, with symptoms including shakiness, sweating, rapid heart rate, and confusion. These are warning signs that the brain is not receiving enough glucose. Severe hypoglycemia, typically defined as a reading below 54 mg/dL (3.0 mmol/L), is a medical emergency that can result in seizures or loss of consciousness.
Withholding insulin is required when the glucose level is 70 mg/dL or below. The focus must shift entirely to immediate treatment using fast-acting carbohydrates to raise the blood glucose back into a safe range. Administering a mealtime dose of insulin when the blood sugar is low should also be avoided until the low blood sugar is first corrected.
Immediate Action Protocol for Treating Low Blood Sugar
When a blood glucose reading is 70 mg/dL or lower, the immediate action required is to treat the hypoglycemia using the “Rule of 15.” This protocol is designed to raise blood sugar quickly and safely without causing a rebound of high blood sugar. The first step involves consuming 15 grams of a fast-acting carbohydrate source.
These sources are chosen because the simple sugars they contain are absorbed rapidly into the bloodstream, providing a near-immediate glucose boost. Foods high in fat or protein, such as chocolate or cookies, should be avoided because they slow the absorption of the sugar, delaying recovery.
- Four ounces (half a cup) of fruit juice or regular soda.
- Three to four glucose tablets.
- One tablespoon of honey.
- One tablespoon of granulated sugar.
After consuming the 15 grams of carbohydrates, the individual must wait 15 minutes before re-checking the blood sugar level. If the blood sugar remains below 70 mg/dL after the 15-minute wait, the process of consuming another 15 grams of fast-acting carbohydrate and waiting another 15 minutes must be repeated. This cycle continues until the blood glucose is above the 70 mg/dL threshold and back into a safe target range.
Once the blood sugar is back in range, it is recommended to eat a balanced snack or meal that contains both carbohydrates and protein, especially if the next planned meal is more than an hour away. If a person experiences severe hypoglycemia, meaning they are confused or unable to swallow, immediate emergency medical intervention is necessary. This typically involves a glucagon injection, which is a hormone that causes the liver to release stored glucose to rapidly raise blood sugar.
Additional Factors Influencing Insulin Decisions
The decision to withhold insulin can be influenced by additional factors even when the blood sugar is above the 70 mg/dL threshold, such as in the 80 to 100 mg/dL range.
Insulin on Board (IOB)
A significant consideration is “Insulin on Board” (IOB), which refers to the amount of rapid-acting insulin that is still active in the body from a previous injection or pump bolus. Ignoring IOB risks “insulin stacking,” where a new dose is administered while the previous dose is still actively lowering blood sugar, leading to an unexpected drop later. For individuals using insulin pumps or advanced calculators, the IOB is often automatically accounted for, but those on multiple daily injections must manually track it. Since rapid-acting insulin can remain active for two to five hours, a conservative approach is necessary if a correction dose was given recently. If the blood sugar is slightly elevated but there is still a high amount of active insulin, a smaller correction or no correction may be advised to prevent a future low.
Exercise and Meal Timing
Planned vigorous exercise is another factor that necessitates a cautious insulin decision. Physical activity increases the body’s sensitivity to insulin and draws glucose out of the bloodstream more quickly. When intense exercise is anticipated, a temporary reduction in the mealtime or correctional insulin dose may be necessary to prevent hypoglycemia during or immediately after the activity. Similarly, the timing and composition of the last meal must be considered; if a meal was delayed or contained fewer carbohydrates than expected, the existing insulin dose might be too strong, requiring a reduction in the next planned dose to maintain safety.