A biosensor identifies a blood type using photoplethysmography (PPG) technology. A PPG circuit obtains a plurality of spectral responses at a plurality of wavelengths detected from skin of a user. A processing circuit determines a blood factor indicator using the plurality of spectral responses. The blood factor indicator may include a signal quality parameter or a ratio R value. A calibration database includes a correlation of the blood factor indicator to a plurality of blood types. The blood blood type of the user is identified using the blood factor indicator and the calibration database.