I'm looking at implementing a driver for some blood glucose meters that actually adhere to official standards. The Continua Design Guidelines act as a type of framework for medical device interoperability. Basically they require devices to adhere to specific standards for USB and Bluetooth LE operation.
While the Bluetooth LE specification is publicly available, including the Glucose Service descriptions required to read data from blood glucose meters, the story for the USB specifications are a little bit more complex. While the USB transport layer protocol, called USB Personal Healthcare Device Class (PHDC) is available publicly, what happens above that layer is described in ISO/IEEE standards that are hidden behind paywalls. Specifically, the .pdf file that describes the glucose meter specific parts is $94 from the IEEE store, $178 if you buy it from the ISO store, $323 from the British Standards store and $194 from the American Standards store. Standards are funded by public money, so it only makes sense that they're publicly available.