The rise in insulin prices, a topic of concern for elderly diabetic patients, has drawn the attention of the Congressional Diabetes Caucus.

Reps. Diana DeGette (D-CO) and Tom Reed (R-NY) sent letters last week to the Pharmaceutical Research and Manufacturers of America, the Pharmaceutical Care Management Association, and America’s Health Insurance Plans, the latter of which is run by former Centers for Medicare & Medicaid Services’ administrator Marilyn Tavenner. The lawmakers noted that average insulin prices have nearly tripled between 2002 and 2013, and asked for a response by July 28.

The global insulin market was $24 billion in 2014, a report last year found, and predicted the it would be above $48 billion by 2020. 

PCMA told Bloomberg BNA last week that “when there are competing substitutable insulins, pharmacy benefit managers are reducing insulin costs. However, there are different types of insulin that don’t impact patients in the same way. As a result, drug companies have significant power to keep prices high.”

Regardless of the groups’ response to DeGette and Reed, signs of change in diabetes management to outcome-based measurements are on the horizon. Medtronic Plc announced on Monday an agreement with Aetna Inc. that payment for insulin pump systems will be tied to health outcomes for diabetes patients. The agreement reflected the “shift towards value-based healthcare,” Medtronic said.

Insulin pumps are often used for patients with type 1 diabetes or for those with type 2 who traditionally checked blood sugar levels several times a day. The pump continuously delivers insulin based on different basal rates.