Patient can present with normal acid-base balance, a single disorder, or multiple combinations of two or three disorders. The pH can be estimated in a patient with a single disturbance using the formulas which describe predicted compensation. Blood gas studies are required for diagnosis and pH estimation when more than one disturbance may be present or when the information is insufficient to allow diagnosis of a single disturbance with confidence (e.g., the patient is unable to give an adequate history). The diagnostic approach to acid-base disorders utilizes information from the history and physical examination, venous blood laboratory studies, and arterial blood gas studies in a stepwise fashion.