A system and method for measuring an amount of blood and/or clotting in a pocket around an implantable device. The system may include a first light source configured to emit light over a first wavelength range. The system may include a first photodetector configured to output a first signal indicative of an amount of the first light received by the first photodetector. The system may include the implantable device and an external device. The implantable device may include one of the first light source and the first photodetector, and the external device may include the other of the first light source and the first photodetector. In some embodiments, the external device may include a controller configured to calculate the amount of blood/or clotting in the pocket around the implantable device using at least a measurement of the first signal.
