Biography: Aldasouqi is professor of medicine and chief of the endocrinology division at Michigan State University College of Human Medicine in East Lansing.
March 07, 2017
4 min read

BLOG: Heathrow Airport, insulin pumps and daylight saving time — What do they have in common?

Biography: Aldasouqi is professor of medicine and chief of the endocrinology division at Michigan State University College of Human Medicine in East Lansing.
You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

We were unable to process your request. Please try again later. If you continue to have this issue please contact

On December 7, 2013, Heathrow Airport was shut down for several hours and hundreds of flights were delayed affecting air travel across Europe. It was not related to terrorist acts or a natural disaster, it was due to a technological glitch.

When technology doesn’t work or when it fails us, chaos may occur.

In Heathrow, there was a glitch in the computer system of the United Kingdom’s air traffic telephone system. According to the BBC, “The National Air Traffic Services said the problem at its Swanwick Centre, in Hampshire, arose in the early hours of Saturday morning when the night-time operation failed to properly switch over to the daytime system.”

 The Air Traffic system’s internal clock failed to switch from p.m. to a.m. All scheduling of flights and everything else that is time regulated at Heathrow could not be executed because events/schedules are time-sensitive in terms of a.m. to p.m. timing in a 12-hour clock format. However, in clocks that use the 24-hour military format, the a.m. to p.m. setting becomes irrelevant.

Many technological devices have internal clocks including phones, computers and coffee makers and in medicine, many devices also have built-in clocks including insulin pumps, making some devices time-sensitive.

Similar glitches to what happened at Heathrow have also occurred in insulin pump internal clocks, which can be set up in either format (12-hour vs. 24-hour).

The first time I became aware of insulin pump clock glitches was coincidental. A few years ago, one of our patients with diabetes using an insulin pump was seen in follow-up and while I was making insulin dose adjustments I noted that the insulin pump clock was 1-hour off. The patient forgot to make the daylight saving time change in her pump, which had occurred several weeks prior. Since this discovery, our diabetes clinic’s staff and providers have developed the habit of checking the time in insulin pumps when downloading and reviewing pumps with patients. Our research group has been reporting on such cases in scientific meetings and reported the findings in a 2014 review article published in The Journal of Diabetes Science and Technology.

Media has been interested in this health-related issue brought about by the daylight saving time ritual that most states practice twice a year, but a few states are considering eliminating this practice. In Michigan, a bill was proposed by State Legislators to eliminate the daylight saving time practice in the state. A reporter from a Michigan news channel used an interview about insulin pump clock glitches to support the bill calling for eliminating the change.

In our scientific papers, we emphasize that, at the time, all commercially available insulin pumps were not GPS-enabled and did not have built-in capabilities to adjust the date/time setting of the device’s internal clock. Although the technological deficiency is being addressed by pump manufacturers, the problem is still prevalent.

Insulin pump and watch
Figure 1. A patient’s insulin pump and my watch: The actual time is 11 a.m., when the patient was being seen in the clinic.

Time and date settings should be set up by users themselves, upon starting the pump for the first time, changing batteries or in any situation where the pump has to be restarted after powering off.

What can go wrong if insulin pump clocks are not set up correctly?

Think about an alarm clock. Traditionally, these clocks are manually set up and in the case of electric clocks, the time has to be reset whenever the power is off for any reason. If a person want’s to wake up at 5 a.m. and the a.m. to p.m. setting is not correct, the alarm will not go off at 5 a.m. but instead at 5 p.m.

If the time setting is not correct on an insulin pump, the delivery of insulin will not be correct. The insulin is delivered through a tiny plastic catheter inserted into the skin in two delivery formats, basal and bolus. The basal delivery provides continuous slow infusion around the clock, and the bolus delivery, a more rapid insulin delivery, provides insulin doses prior to meals.

In order for the right dose of insulin to be delivered at the right time, the time setting of the pump’s clock should be consistent with the ambient time. If not, incorrect dosing will occur and this can be harmful. The daylight saving time glitch (1-hour difference) may not result in discernible difference in insulin dosing, except if different bolus doses are used for different meals, as explained in the review article referenced in this blog. This issue is particularly relevant to lunch in the spring’s daylight saving time change, advancing by 1 hour. Typically, pump users set up the lunch pre-meal bolus dosing to start at 11 a.m., since the average lunch time starts after 11 a.m. and typically by noon. During the spring daylight saving time change, if a patient’s pump’s time does not advance, the patient will get the breakfast bolus for lunch. If the breakfast bolus is higher than lunch, hypoglycemia may occur in the afternoon.

However, the a.m. to p.m. dose is likely to be more harmful than the daylight saving time glitch, in various ways. For example, if basal rates between night and day are quite different, the doses would be reversed between day and night. A special risk for hypoglycemia will occur at night if higher rates intended for daytime use are delivered at night.

The next daylight saving time change is coming, Sunday, March 12th.


Aldasouqi SA, Reed AJ. J Diabetes Sci Technol. 2014;doi:10.1177/1932296814541811.