Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Metabolic acidosis
Although blood gas sampling is not always essential for the diagnosis of acidosis, a low pH (in either a venous or arterial sample) does support the diagnosis. If the pH is low (under 7.35) and the bicarbonate levels are decreased (<24 mmol/L), metabolic acidemia is present, and metabolic acidosis is presumed. If the patient has other coexisting acid-base disorders, the pH may be low, normal or high in the setting of metabolic acidosis. If a setting of a cause for metabolic acidosis being noted in the patient's history, a low serum bicarbonate indicates metabolic acidosis even without measurement of serum pH.