Priming an insulin pen is a necessary action performed immediately before an injection. This step involves expelling a small, set amount of insulin into the air to prepare the device for use. Priming ensures the needle is clear and that the pen’s mechanism is filled with insulin, not air. This preparatory action guarantees the accurate delivery of the prescribed medication.
The Standard Priming Unit Amount
For the majority of pre-filled and reusable insulin pens, the standard recommendation for priming is to dial two units of insulin. This amount is generally cited as sufficient by manufacturers to clear the small air pockets that can naturally form within the pen and needle assembly. Pens such as the Humalog KwikPen or the Lantus Solostar often follow this two-unit guideline. While two units is the general rule, it is best practice to consult the specific instructions provided by the pen manufacturer or your healthcare provider.
Why Priming Is Essential For Accurate Dosing
Priming the insulin pen serves two functions that directly impact dosing accuracy. The first is the removal of trapped air from the needle and the cartridge area. If air bubbles remain in the system, they occupy volume that should be filled by insulin, which can lead to an under-dosing when the medication is injected. Expelling the two-unit prime ensures that the medication delivered is pure insulin, not a mix of insulin and air.
The second function is to confirm the patency of the needle, ensuring that it is properly attached and not blocked. When the two units are injected into the air, a drop of insulin should visibly appear at the needle tip, confirming the pathway is open.
Troubleshooting and Confirmation Steps
A successful prime is visually confirmed by observing a small, distinct drop of insulin at the tip of the needle after the two units have been expelled. This visible droplet is a physical confirmation that the pen’s internal mechanism is functioning correctly and that the medication can flow freely. If no drop appears after dialing the standard two units and pressing the injection button, this indicates a potential issue that requires troubleshooting before proceeding with the full dose.
Troubleshooting a Failed Prime
The most common reason for a failed prime is a blocked or improperly attached needle. The first corrective action should be to replace the existing needle with a new, sterile one. After attaching the new needle, the priming process must be repeated by dialing and expelling another two units of insulin.
If a visible drop still does not appear after changing the needle and re-priming, the pen may be defective, and you should not use it for injection. Skipping the priming step carries a significant risk of injecting an inaccurate dose, which could lead to complications with blood sugar management. Attempting to inject with a blocked needle can result in a painful injection or the full dose leaking out.