Why and How to Prime Your Insulin Pen?

While insulin pens are easy to use and very convenient for people with diabetes who receive insulin therapy, failure to use them correctly can significantly impact blood glucose management. 

Yet, according to the American Diabetes Association, diabetic patients often forget to prime their insulin pen[1].

Let’s discuss why priming your insulin pen is important and how to do it correctly. 

Related article: Does insulin need to be refrigerated, and how to store it properly?

Why You Must Prime your Insulin Pen

Priming means preparing your pen for insulin injection. It’s done by injecting a few units of insulin into the air to get rid of air bubbles and make sure the needle is functioning correctly. It must be done before every insulin shot. Priming isn’t just for insulin pens: any injection device, pen, or syringe, must be primed before injecting any medication into the body.

Related article: A step-by-step guide to using insulin pens for injection

Getting air bubbles out of the pen

The main reason why you must prime your insulin pen before an injection is to remove air bubbles from the needle and cartridge (insulin reservoir) and ensure you’re getting your full dose of insulin.

Air bubbles in insulin pens are very common. Changes in insulin temperature, atmospheric pressure, shaking, or vibrations may result in bubble formation.

When there are air bubbles in your insulin pen or needle, they take up the space of the insulin. If you do not remove them before your subcutaneous injection, you’ll be injecting too little insulin (your dose of insulin – the volume of the air bubbles). 

Ultimately, removing air bubbles by priming your insulin pen considerably improves insulin dose accuracy and blood sugar control. 

Related article: Insulin Pen Needle Types & Sizes, The Ultimate Guide!

Make sure the needle works

Ensuring your pen and needles work correctly is the other reason why you must prime your insulin pen before every injection.

As you know, insulin pens work with disposable needles, and you must use a new one for each injection. Priming the pen after attaching a new needle and sending insulin into the air allows checking that the needle is open and working.

While rarely, disposable insulin pen needles may be damaged, unopened, or blocked. It's also possible that you haven't screwed the needle onto the pen correctly, and the insulin can't go out as it should.

Priming your pen is also a way to ensure it's not jammed or defective, which rarely occurs but could have serious consequences. Think about a broken insulin reservoir, a dosing knob that isn’t working, or no insulin is delivered when the button is pressed, for example. By priming your pen before the injection, you can see for yourself that insulin is dropping out of the pen normally.

Related article: A beginner’s guide to basal and bolus insulin

What happens if you don’t prime? 

The main risk of not priming your insulin pen before every injection is getting too little insulin. The direct consequence is a partial (if your pen was filled with air bubbles) or total (if your pen is not working) loss of blood sugar control and hyperglycemia (high blood sugar).

Air bubbles in an insulin pen pose no direct threat to your health, and injecting air bubbles subcutaneously won't harm you. However, if you forget to prime your pen and remove the bubbles before the injection, you’d be getting less insulin than you should (your dose of insulin – the volume of the air bubbles). Ultimately, this would lead to higher blood sugar levels.

Finally, skipping the priming step increases the risk of missing an insulin dose. For example, if the needle is blocked or the pen faulty, you may not notice it when injecting it into your body, but you would have been able to see it during the priming step. 

Related article: What happens if you miss a dose of insulin?

How to Prime your Insulin Pen? 

Priming an insulin pen is fairly easy. Diabetes nurses and doctors must have shown you at the hospital. But here's a step-by-step reminder of how to prime an insulin pen correctly.

Priming an insulin pen step by step 

1. Screw the disposable needle onto the pen.
2. Pull off the outer cap and inner cap of the needle (you can discard the inner cap but keep the outer one as you will need it after the injection).
3. Select 2 units of insulin with the dose knob.
4. Hold the insulin pen with the needle pointing up.
5. Tap the insulin reservoir (or cartridge) with your fingers so the air bubbles come to the top.
6. Shoot insulin in the air by pushing the injection button all the way (like for an injection).
7. You should see at least a drop of insulin going out of the needle.
8. If you do not see any insulin, repeat the priming process from steps 3 to 6.
9. You may need to prime several times, but if no insulin flows after several attempts, your needle may be clogged. Try with a new one.
10. If the priming is still unsuccessful with a new needle, your insulin pen may be defective. Do not use it. Take it back to the pharmacy and ask for help.

Related article: How to Calculate Your Insulin Dose Correctly?

How many units to prime an insulin pen? 

The minimum number of units to prime an insulin pen with is 2, but some manufacturers recommend priming with 3 units of insulin.

An insulin pen that you use for the first time or a pen with a lot of air bubbles may need to be primed with more insulin units. In any case, always prime until you can see a drop of insulin at the tip of the needle and there are no more air bubbles.

Related article: How to convert insulin units to mL?

Do you prime insulin pens every time? 

Yes, you must prime your insulin pen before every injection. While it may seem like a waste of insulin, dosage accuracy is much more important.

Think about it this way: for someone who needs several daily insulin injections, a 1–2-unit margin of error quickly adds up. It can be up to 10 units of insulin you're not receiving each day. That makes a big difference and can explain why blood glucose management is not optimal.

What about you? Do you prime your insulin pen before every injection?

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