A capsule employing components for detecting blood content or hemoglobin concentration within tissue forming a lumen in vivo advantageously permits screening or diagnosis of certain diseases. In one embodiment, the capsule includes a light source for intermittently illuminating a region of tissue and a light detector for receiving interacted light from the tissue and hemoglobin therein. Methods of validating data of interacted light signal are also disclosed. A power conservation method of detecting the blood content values at different rates is further disclosed.
