Storage Conditions of Insulin in Domestic Refrigerators and Carried by Patients—Insulin Is Often Stored Outside Recommended Temperature Range

Objective: Not much is known about how patients with diabetes store their insulin in daily life. Objective of our study was to monitor temperature of refrigerated and carried insulin in industrialized countries to investigate how often storage conditions do not meet the manufacturers’ recommendations.

Method: Patients (n=338; 46% in the U.S., 41% in the EU) put a total number of 400 temperature loggers (MedAngel ONE, NL) next to their insulin into their refrigerator or diabetes bag. Temperature was measured every 3 minutes (up to 480 times/day). Measurements were sent to an app and stored in a protected online database. Whenever temperature exceeded the recommended range (2-8°C for refrigerated insulin, 2-30°C when opened/carried), the user was notified by an alarm. Data was collected from November 2016 to February 2018 with an average protocol length of 49 days.

Results: Temperature logs from individual sensors were analyzed (230 for refrigerated, 170 for carried insulin). Deviations were found in 315 (78.8%) logs (230 (100%) refrigerated, 85 (50%) carried). For refrigerated insulin, temperature recorded by an average sensor was out of the 2-8°C range 11.31% of the time (10.10%-13.10%; 2 hours 43 minutes/day) with an average deviation of 3.68K (SD 5.02K). For carried insulin, temperatures were out of 2-30°C range 0.54% of the time (0.48%-0.64%; 8 minutes/day) with an average deviation of 1.11K (SD 1.24K). 17% of sensors measured temperatures <0°C (57 refrigerated, 9 carried).

Conclusion: Long-term storage conditions of insulin are known to have an impact on its blood-glucose lowering effect. These observational data showed that in a significant number of cases insulin was exposed to temperatures outside the recommended range, especially when refrigerated. Thus, domestic refrigerators may pose an underestimated risk for insulin quality. The extent of how temperature deviations in storage affect insulin efficacy and patient outcomes needs further systematic investigation.