Insulin is a naturally occurring, glucose-lowering hormone used by many people with diabetes to control their blood sugar. In people with Type 1 diabetes, supplemental insulin makes up for the insulin that is not produced by the body. People with Type 2 diabetes may need to take insulin if they cannot maintain adequate blood sugar control with other medications.
Insulin is manufactured to be identical to the insulin produced by the human pancreas. These synthetic insulins can work from a few hours (rapid-acting insulin) to a whole day (long-acting insulin). They are typically injected via a needle or pen.
Guidelines for proper insulin storage
All insulins must be stored with care to ensure that they remain safe and effective. Improper storage could result in the breakdown of insulin, affecting its ability to effectively and predictably control your blood sugar level.
Depending on the type of insulin you are prescribed, there may be some subtle differences in how best to store it and how long it will last once open. Ask your doctor or diabetes educator for specifics on how to store your own insulin prescription.
Here are some general rules that reflect best practices for properly storing insulin:
—All insulins are sensitive to temperatures that are too high or too low. Once you receive your insulin prescription, you should store all the supplies you've received in the refrigerator.
--Once you open a new vial (meaning once you stick a needle in the vial) or pen, use a Sharpie to note the date you opened it right on the packaging. This will help you remember when to stop using it. Throw the insulin away 28 days after opening it.
--Once you open a vial, keep it stored in the fridge or at room temperature. Be aware that injecting refrigerated insulin may be painful.
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--Keep an insulin pen refrigerated until you open it; after that, you can store it at room temperature.
--Ask your doctor if your particular insulin has a shorter or longer lifespan. Some insulins must be used in as little as 10 days.
--If you suspect your insulin was ever frozen, you should not use it. Insulin could freeze if it was left outside in extreme cold temperature, for example if it was delivered on a cold day and stayed outside for a while, or if it was left in your car. But insulin could also freeze in your refrigerator. Research presented at the European Association for the Study of Diabetes meeting in Berlin showed that domestic refrigerators may have unexpected temperature fluctuations. To ensure that your refrigerator keeps a constant temperature and does not go below the freezing point at any time, keep a thermometer in the fridge to check for a stable temperature of 39 F (or 4 C).
--Insulin is also sensitive to hot temperatures, so do not leave it outside in extreme heat. This could happen in the summer, especially if you leave your insulin in the car for several hours, or you keep a spare insulin sample in the glove compartment of the car as backup.
--Exposure to sunlight can also degrade insulin.
--Always check the expiration date and do not use expired insulin.
--Inspect your insulin before each use. Look for changes in color or clarity. Look for clumps, solid white particles, or crystals in the bottle or pen. Insulin that is clear should always be clear and never look cloudy.
Finally, if you have any doubts, start a new vial or pen to avoid unpleasant surprises.
(Elena Toschi, M.D., is a contributor to Harvard Health Publications.)