The systemic disease that an oral physician suspects is usually of greater significance to the patient than the oral lesion with which he presented.Laboratory investigation plays a very important role in diagnosing various oro-mucosal lesions, various oral manifestations of systemic disease which manifest in the oral cavity & to treat them appropriately. Laboratory investigation has become an important part of medical diagnostic procedure by adding its objective information to the more subjective history and physical examination of the patient. In last few decades laboratory investigation...