Insulin at Risk From Variable Temperatures of Home Refrigerators

Becky McCall

October 04, 2018

BERLIN — Domestic refrigerators fail to keep insulin within the manufacturer-recommended temperature range in a significant number of cases, raising the possibility that refrigerators may pose an underestimated risk for insulin quality, shows an observational study conducted in industrialized countries.

Study lead Katarina Braune, MD, from Charité-Universitaetsmedizin Berlin, Germany, presented the findings in a poster at this year's European Association for the Study of Diabetes (EASD) Annual Meeting, and also reported them at a press conference here.

"Nearly every dataset relating to fridge storage showed excursions from the recommended range that are below 2° C and above 8° C, and even some excursions below 0° C. We were surprised that every dataset showed this pattern," she remarked.

"Our results show that refrigerated insulin was exposed to more temperatures out of range than insulin that is carried around [on the person]."

During the press conference, Bastian Hauck — who has type 1 diabetes and is the founder of online diabetes forum DeDoc, as well as being active on Twitter (@bast-ha) — said that he often travels around the world with his insulin, and temperatures often varied outside of the recommended range for storage.

"It would be helpful to have a system that would allow a patient to know if their insulin was still viable if they thought it had been exposed to extreme temperatures," he pointed out. "What scares me from these results is that I always viewed my fridge as providing safe storage. Sometimes I have a year's supply of insulin in my fridge, and now it's at risk."

Braune said this study did not examine how variations in storage temperature might affect the performance of insulin and the consequent effect for patients — more work is needed on this, she noted.

The company who made the sensors used in this study is developing a thermometer for use in monitoring insulin.

Fridge Is a More Variable Environment Than Thought

Not much is known about how patients with diabetes store their insulin in daily life. Braune and colleagues aimed to monitor the temperature of refrigerated insulin as well as that carried on the person to investigate how often storage conditions deviate from manufacturers' recommendations.

There were 338 participants, mainly split between the United States and Europe, who placed 400 temperature loggers/sensors (MedAngel ONE) next to their insulin, either in the refrigerator or in their "diabetes bag."

Readings were taken every 3 minutes. Data were sent to an app and stored in a secure online database. If the recorded temperature was outside the recommended storage range (2° - 8° C for refrigerated insulin, 2° - 30° C when opened or carried as a spare), an alert was triggered. Patients were monitored for an average of 49 days between November 2016 and February 2018.

For domestic refrigerators, the results showed that the recorded temperature by an average sensor was out of the recommended range of 2° - 8° C for 11.31% of the time, equivalent to 2 hours, 43 minutes per day. Specifically, insulin was stored below 2° C for 1.1 days per month; and insulin was stored below 0° C for 3 hours per month. It was within the manufacturer recommended range of 2° - 8° C for 26.6 days per month, and it was kept at above 8° C for 2.3 days per month.

For carried insulin, stored temperatures were out of recommended range (2° - 30° C) for 0.54% of the time, equivalent to an average of 8 minutes per day. Insulin was kept below 2°C for 2.6 hours per month, and kept within 2° - 30° C for 29.8 days per month. It was kept above 30° C for 1.3 hours per month.

"Our data look at the deviations from [recommended storage] temperature," noted Braune, but the extent to which these variations in storage temperature affect the potency of insulin and patient outcomes "needs further systematic investigation," she added.

"If the effect is 100% lost — for example, if the insulin is frozen — it might not have the glucose-lowering effect required," she explained.

With rising temperatures, "It is likely to be a gradual effect with heat when fibrils are being irreversibly damaged, and this might mean the desired insulin effect is slower than normal. Some insulin vials might not be so potent as others. But we don't know this for sure and need to research this."

Company Is Working on Thermometer to Monitor Insulin Temperatures

Commenting on the study results, Bernhard Gehr, MD, senior diabetologist at Fachklinik Bad Heilbrunn, Germany, said: "The study is important because it was conducted in the real world and it highlights significant potential problems with insulin safety.

"We have millions of insulin dependent patients. It has been shown previously that insulin quality is variable, with shocking deviations in insulin concentration, but the reason for this has not yet been identified," Gehr wrote in an email to Medscape Medical News.

"Storage and transport conditions may play a major role, and this is clinically important. What we need next is real world data that address how the observed conditions might impair insulin quality," he added.

MedAngel ONE, the company that manufactures the sensors used in the study, is commercializing a thermometer that connects to a smartphone app via Bluetooth.

"The cost of this is not yet covered by German health insurance companies," Gehr pointed out.

"Based on these findings, it might also be recommended not to store insulin in the butter or dairy compartment nor in the vegetable drawer, but rather in the middle shelf or the meat drawer," he said.

Dr Braune has consulted for Dexcom, Medtronic, Novo Nordisk, and Roche. She is an advisory board member for Medtronic IMPACT. Dr Gehr has disclosed no relevant financial relationships.

European Association for the Study of Diabetes (EASD) 2018 Annual Meeting. Poster and abstract 891, presented October 3, 2018.

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