Establishing a relationship between the measurand and key parameters affecting the propagated light in a waveguide provides useful information for functional verification and testing of optical biosensors. The proposed mathematical model can estimate the expected responses which -independent of the sensor operation -can be compared against the measured responses to identify inconsistencies in the sensor performance. A noticeable drift in the estimated light intensity from that measured at the detector is an indication of abnormality in the sensor's functionality.