Performing measurements using sensors of a medical device system

This disclosure is related to devices, systems, and techniques for performing patient parameter measurements. In some examples, a medical device system includes an optical sensor configured to measure ambient light and a tissue oxygen saturation parameter and processing circuitry configured to determine that a current measurement of the tissue oxygen saturation parameter is prompted and control the optical sensor to perform an ambient light measurement associated with the current measurement of the tissue oxygen saturation parameter. The processing circuitry is further configured to determine, based on the ambient light measurement, at least one of whether to control the optical sensor to perform the current measurement of the tissue oxygen saturation parameter, when to control the optical sensor to perform the current measurement of the tissue oxygen saturation parameter, or whether to include the current measurement of the tissue oxygen saturation parameter in a trend of the tissue oxygen saturation parameter.