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Insulin Basics: What it is, How to use it, and Prescription Savings

*Disclaimer: This article is not intended to provide medical advice, diagnosis, opinion, treatment or services. This blog is meant to provide general information for educational purposes only. The information provided in this blog is not a substitute for medical care and should not replace advice from your healthcare provider.*

cover page for insulin basics blog

When you have type 1 diabetes, insulin therapy becomes an essential component of your everyday life and management. However, not many people with diabetes understand the complexities of what insulin is or how it works. Insulin therapy is incredibly intricate and can be difficult to understand. This blog post will guide you through the basics of understanding insulin so you effectively utilize your insulin and keep your blood sugars within target.

What is insulin?

Insulin is a hormone that is typically produced by the pancreas that helps regulate blood sugar levels by helping glucose in the bloodstream enter the body’s cells for energy. When you have type 1 diabetes, insulin therapy is mandatory to replace the insulin their pancreas is no longer producing and keep blood sugar levels within range.

Characteristics of Insulin

Insulin can be characterized by the following:

  • Onset: how quickly the insulin begins to lower blood sugar levels

  • Peak: how long it takes to achieve maximum impact

  • Duration: how long it stays in the bloodstream

  • Concentration: strength of insulin

Different Types of Insulin

There are several different types of insulin available and they differ depending on how quickly and how long they impact blood sugar levels. The five main types of insulin include: ultra-rapid, rapid-acting, short-acting, intermediate-acting, and long-acting insulin.

Ultra-Rapid Acting Insulin:

Ultra-rapid acting insulin begins working within 2.5 to 5 minutes after injection and stays active for 2 to 4 hours after injection. This insulin is often used at mealtimes and in some cases up to 20 minutes after eating. Ultra-rapid acting insulins include lyumjev (insulin lispro-aabc) and fiasp (insulin aspart).

Rapid-Acting Insulin

Rapid-acting (fast-acting) insulin begins working within 15 minutes after injection and stays active for about 2 to 4 hours after injection. This insulin is often used before mealtimes. Humalog (insulin lispro), Novolog (insulin aspart), Apidra (insulin glulisine) are considered rapid-acting insulin.

Short-Acting Insulin

Short-acting, or regular insulin begins working 30 to 60 minutes after injection and stays active up to 5 to 8 hours after injection. This insulin is often injected prior to mealtimes, but is slower to start working that rapid-acting insulin. Regular (R) or novolin are examples of short-acting insulin.

Intermediate-Acting Insulin

Intermediate-acting insulin begins working 1 to 2 hours after injection and stays active for 12 hours. This insulin isn’t commonly used, but your healthcare provider may prescribe it. NPH is a type of intermediate-acting insulin.

Long-Acting Insulin

Long-acting insulin begins working 1 to 2 hours after injection and stays active for 24 hours. This insulin is considered to be background insulin to mimic the pancreas’s function of producing small amounts of insulin throughout the day. Long-acting insulins include: lantus (insulin glargine), levemir (insulin detemir), Toujeo (insulin glargine), Tresiba (insulin degludec) and basaglar (insulin glargine).

How do you take insulin?

There are a few different ways to administer insulin. Most people with diabetes self-administer by injecting with a syringe or insulin pen. Other methods of administering insulin include: insulin pumps, injection port, and inhaled insulin.

graphic of insulin injection sites

Insulin Injection Sites

There are several areas of the body where insulin may be injected. Insulin is typically injected into the subcutaneous tissue, the layer of fat directly under the skin. Common injection sites include:

  • Abdomen

  • Upper Arms

  • Thighs

  • Lower Back, Hips, Or Buttocks

Insulin Absorption Speed

Some portions of the body will absorb insulin at different rates. Insulin enters the bloodstream quickest from the abdomen followed by upper arms, lower back, and thighs. However some factors like exercise can increase the absorption rate of insulin which can be helpful in some cases.

Rotating Insulin Injection Sites

It is important to avoid injecting insulin into the same site over and over. This can cause skin irritation and reduce the effectiveness of the insulin absorption. Rotating injection sites can help ensure you are not injecting in the same exact spot every time.

photo of insulin vials

How should you store insulin?

To store insulin, it is recommended that unopened insulin be stored in a refrigerator at approximately 36-46 degrees Fahrenheit. You should avoid placing insulin in the freezer or directly on ice. Insulin that is opened may be left unrefrigerated at room temperature (59-86 degrees Fahrenheit) for up to 28 days and continue to work. Insulin loses some of its effectiveness when exposed to extreme temperatures (both hot and cold).

How to use basal insulin?

Basal insulin (aka background insulin) is a set amount of insulin that you receive around the clock. The liver is constantly releasing glucose into the bloodstream throughout the day, usually between meals and overnight, when waking up, and during periods of high stress. With diabetes, you must get this insulin through either long-acting injections or incremental doses of fast-acting insulin through an insulin pump.

Signs your basal insulin needs adjusting

Your basal rate tests may need to be adjusted for a number of different reasons like changes in physical activity, growth, hormones, stress, sickness, and others. The ultimate goal of your basal insulin is to keep your blood sugars stable. If you find that your blood sugars are having high levels of fluctuation, it may be a sign that something needs adjusting:

  • Blood Sugars rise or fall overnight: goal is for blood sugars to stay within +/-30mg/dL or about 2mmol/L overnight

  • Blood sugars rise or fall between means: goal is for your basal to bring your blood sugars back into range 2 hours after eating. If your blood sugars return to range after 2 hours post-meal and continue to fall or slowly rise back up, your basal rate may need to be adjusted.

If you are experiencing either of these, you may want to give your care team a call to discuss making adjustments to your settings.

insulin injection with a pen

How to use bolus insulin?

In addition to background insulin, insulin is also required to cover the carbohydrates in meals and snacks and to return blood sugar back to target range when blood sugars are too high which is called bolus insulin. Bolus insulin needs to act quickly to bring blood sugars back into range in a timely manner so ultra-rapid or fast-acting insulin is used due to their quick onset and shorter duration compared to other insulin types.

What is an insulin to carb ratio?

When you are first diagnosed with type 1 diabetes, you may be given a sliding scale of insulin. This sliding scale varies the dose based on what your blood sugar level is, but you take the same amount of insulin no matter how many carbohydrates you plan to consume at your meals. This method assumes that a consistent amount of carbohydrates is eaten at meals, but realistically carbohydrate intake can vary significantly between meals and snacks everyday.

An insulin to carb ratio indicates how many carbohydrates one unit of insulin will provide coverage for. An insulin to carb ratio allows for more flexibility with insulin dosing because you are matching your insulin needs specifically to the grams of carbohydrates in each particular meal or snack.

An example of an insulin to carb ratio of 1:8 means that 1 unit of insulin would cover 8g of carbs. So if you decide to consume a meal with 72g carbohydrates, you will need to take 9 units of insulin (72g of carbs divided by 8= 9 units).

If you do not have an insulin to carb ratio, your healthcare provider, registered dietitian or diabetes educator can help you with choosing a starting ratio.

What is a correction or sensitivity factor?

A correction or sensitivity factor is used to calculate the amount of insulin needed to bring blood sugars into range. This will adjust the amount of insulin given depending upon whether blood sugar levels are too high or too low before a meal. Your care team can work with you to define what your target blood sugar range is and help you determine your insulin correction factor as well.

What if you can’t afford your insulin?

The price of insulin continues to rise for people with and without insurance in the United States. On top of navigating the intricacies of health insurance and confusing patient assistant programs, it can be challenging trying to figure out how to afford your prescribed and preferred diabetes medication. Below are resources that can potentially offset the financial costs of insulin:


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