By Kelly Close
Blood glucose checks can be frustrating. Sometimes I think I am doing everything right - I know my target, I know the carb count of any food I'm about to eat, I know my insulin-to-carb ratio, and I understand my insulin sensitivity.
But even if I pay close attention to these factors, my blood glucose results can be mysteriously higher or lower than I expected. What people may not know is that of the many things that can influence blood glucose, insulin absorption is one of the most important. Let's look at some common misconceptions:
MYTH: My blood glucose should not be affected by where I take my shot, or where I insert the catheter for my pump. After all, insulin going in is insulin going in!
FACT: Actually, the injection site you pick can affect how quickly the insulin is absorbed. For example, insulin is usually absorbed faster in the abdomen - sometimes almost twice as fast - than in other sites such as the thigh or arm.
MYTH: Insulin will always be absorbed faster if I inject in my abdomen.
FACT: Well, not exactly. There are additional things to consider, says Dr. Howard Wolpert of the Joslin Clinic:
MYTH: Temperature does not significantly affect insulin absorption.
FACT: Actually, heat can cause blood vessels to increase in size, as Wolpert writes in his book Smart Pumping. So avoid taking a hot bath, shower or sauna after you take insulin. It could cause you to have a low blood sugar reaction. Gloria Yee, RN, CDE at USCF also suggests that you avoid cooling the injection area (using cold packs, for example). This can slow the absorption rate.
MYTH: Injection site and temperature are the only things that affect insulin absorption.
FACT: That’s not quite true … there are rarely “absolute” rules with respect to diabetes, as most of you probably know! Gloria Yee notes that other factors can affect insulin absorption, such as:
MYTH: The type of food you eat does not affect insulin absorption.
FACT: True, but it can affect your blood sugar. Your body processes different foods at various rates. This can affect the relationship between your blood sugar and the insulin you take. For example, foods that are high in fat are typically absorbed slowly. Your insulin can “run out” before the food is absorbed entirely, causing a large swing in blood glucose. That’s another reason to go easy on foods like pizza and fries! Also, foods with a high glycemic index (such as rice) enter your system faster than foods with a low glycemic index, such as meat.
MYTH: As long as I use up my insulin within a month of receiving it, I don’t have to worry about how I store it.
FACT: It’s easy to forget, but insulin storage is critical to ensure its stability, which can affect absorption. Check the insulin package insert for storage guidelines. Vials that are currently in use can be kept at room temperature – avoid exposing them to extreme heat or cold. Keep all other unopened vials in the refrigerator. Never put your insulin in checked baggage when you fly: the luggage hold could get a lot colder than your fridge. Insulin that has been frozen and thawed should be thrown away, no exceptions, If you leave your opened insulin vials at room temperature, be sure the sun does not shine on them and heat up the contents while you’re out for the day. It’s a good idea to get into the habit of inspecting vials currently in use to ensure that the insulin has not crystallized. If the insulin that’s supposed to be clear has gone cloudy, or you can see what looks like salt inside the vial, do not use it! The insulin may be less effective, it might act unpredictably, or it might not work at all.
This may seem like a lot to keep track of, but remember: knowledge is power. The smarter you are about your diabetes, and insulin in particular, the better choices you can make to help you stay in good control. As always, be sure to check with your healthcare team before making any changes to your insulin injection routine.
Kelly L. Close is a medical writer with type 1 diabetes. She attends over 30 scientific and industry diabetes conferences per year.
Important note: The content of this article is not intended to be a substitute for professional medical advice, diagnosis or treatment. Do not disregard your doctor's advice or delay in seeking it because of something you have read on this article.