OB+ (occult blood positive)

OBS (organic brain syndrome)

OBS (obstetrics)

OBS/OBD (organic brain syndrome/organic brain disorder)

obsd (observed)

obst (obstruct, obstruction)

OBT (over-bed table)

OBUS (obstetrical ultrasound)

OC (oleoresin capsicum)

OC (obstetrical conjugate)