Tens of thousands of people with diabetes worldwide are receiving letters from Medtronic warning of a potential safety risk involving damage to an external component on the medical device maker's most advanced insulin pumps, the MiniMed 600-series line.

Medtronic is warning people who use MiniMed 620G, 630G, 640G and 670G insulin pumps that the devices may deliver too much or not enough insulin if an exterior mechanical component on the top of the device called the retainer ring becomes damaged from dropping or banging the device. A picture of the ring is included on Medtronic's safety letter.

The Minnesota-run company, whose diabetes division is based in California, said customers should stop using a pump if the retainer ring is loose, damaged or missing. A spokeswoman said Medtronic will replace pumps that have damaged retainer rings.

"Based on our analysis of damaged retainer rings from past insulin pumps, we made improvements to the pump design to better withstand the accidental dropping or bumping of a pump on hard surfaces," spokeswoman Pam Reese said in an e-mail Thursday.

Globally, Medtronic has received one report of a patient being hospitalized for an issue involving a retainer ring and one reported death "which we have investigated and have been unable to exclude as being associated with this issue," Reese wrote.

Insulin is a natural hormone that lets the body use sugar in the blood or store it for later. People who have diabetes inject manufactured insulin as a drug, to prevent the damaging health effects of having too much or too little blood sugar. An insulin pump is a body-worn medical device that administers small doses of insulin throughout the day, as well as larger doses before or after meals or exercise to control blood-sugar levels.

Medtronic's MiniMed 600-series pumps have an opening at the top of the device where the user plugs in a small reservoir filled with insulin. The reservoir is supposed to lock securely into the insulin port on the pump, by sealing against the retainer ring covering the top edge of the port.

"If the reservoir is not properly locked into the pump, it could lead to over- or under-delivery of insulin," the Medtronic safety letter said. "If the pump retainer ring is broken or becomes detached from the pump, and the user inserts the reservoir back into the pump while the infusion set is still connected to the body, it could result in a rapid infusion of insulin. … The under delivery of insulin could occur if the reservoir is not properly locked in place … preventing the pump from pushing the expected insulin into the body."

If an insulin reservoir doesn't lock into the pump, or if the retainer ring is loose, damaged or missing, the letter cautions users not to plug the reservoir into the pump while connected to the body because a large dose of insulin could unintentionally be given.

Users with a broken retainer ring can go to info.medtronicdiabetes.com/PumpRing for more information, or call the 24-hour technical support line, 1-877-585-0166.

"Medtronic will replace pumps that have damage to the retainer ring and advises customers to examine their pump retainer ring during each infusion set and reservoir change to ensure the reservoir locks in place," Reese wrote.

Joe Carlson • 612-673-4779