Insulin is a medication for many individuals managing diabetes, and its effectiveness relies on proper storage. Concerns about how to store insulin, particularly after removal from refrigeration, are common. Maintaining insulin’s stability is important, as temperature fluctuations can impact its ability to lower blood glucose levels.
General Guidelines for Insulin Storage
Proper insulin storage preserves its potency and ensures it works as intended. Unopened insulin vials or pens should be stored in a refrigerator at temperatures between 36°F and 46°F (2°C and 8°C) until their expiration date. This cool environment maintains the integrity of the insulin protein, preventing premature degradation. Freezing insulin must be avoided, as this can irreversibly damage its structure, rendering it ineffective.
Once opened, or when in use, storage recommendations change. Most opened insulin can be kept at room temperature, between 59°F and 86°F (15°C and 30°C), for up to 28 days. Room temperature storage is often preferred because injecting cold insulin can cause discomfort. However, protect insulin from direct heat, sunlight, and extreme temperatures, which can accelerate its breakdown.
Re-refrigerating Insulin
The question of whether insulin can be placed back in the refrigerator after being removed is common. For unopened insulin briefly out of refrigeration, returning it to the fridge is acceptable, provided it has not been exposed to temperatures above 86°F (30°C) for an extended period. Unopened insulin vials and cartridges can withstand temperatures up to 77°F (25°C) for several months without significant potency loss, or up to 86°F (30°C) for up to 28 days.
However, for opened insulin in use, re-refrigerating it will not extend its shelf life beyond the initial room temperature allowance of 28 days. Once an insulin pen or vial has been in use and kept at room temperature, its stability period begins, regardless of subsequent re-refrigeration. Repeated temperature fluctuations from moving insulin in and out of the fridge can contribute to insulin protein degradation over time. Always consult specific manufacturer guidelines.
Recognizing Compromised Insulin
Regardless of how insulin has been stored, it is important to identify if it has become compromised. Visual inspection is a method for detecting issues. Most types of insulin should appear clear and colorless. If clear insulin appears cloudy, discolored, or contains visible particles, clumps, or “strings,” it should be discarded.
Some insulin types, such as NPH insulin (e.g., Novolin N, Humulin N), are naturally cloudy. For these, look for changes like a frosted appearance inside the vial or pen, or if the cloudiness is uneven with separation or clumps. Beyond visual signs, unexplained high blood sugar levels, despite proper insulin administration, can indicate that the insulin has lost its potency. In such cases, replace the insulin with a fresh supply and monitor blood glucose levels closely.