Value of the anion gap in clinical diagnosis and laboratory evaluation.

We report the incidence of normal (50.4%), increased (46.7%), and decreased (2.9%) anion gap among hospitalized patients in a retrospective study. The mean and range of increased anion gaps were 25 and 19-28 mmol/L. Values exceeding 30 mmol/L were uncommon and may indicate either acidosis or laboratory error. The most common causes of the increased anion gap among patients were chronic renal failure, congestive heart failure, malignant neoplasm, and diabetes mellitus. Increased anion gap in this study may be due to excess acids along with decreases in sodium, chloride, and carbon dioxide. The mean and range of decreased anion gap were 6 and 3-8 mmol/L. Anion-gap values less than 3 mmol/L were uncommon (one of 500 cases), and a high incidence of such values may indicate laboratory error. Nephrotic syndrome, liver cirrhosis, intestinal obstruction, and severe hemorrhage were the common disorders associated with decreased anion gap, which resulted from hypoalbuminemia and hyponatremia. Although most patients with decreased anion gap had hypoalbuminemia, hypoalbuminemic patients did not necessarily have decreased anion gap.