Which statement best describes the purpose of the anion gap in clinical chemistry?

• A. It diagnoses liver disease
• B. It detects some disease states and helps evaluate electrolyte disturbances
• C. It measures chloride concentration
• D. It directly measures unmeasured anions

Answer: (B)

The anion gap is a calculated clue used to reveal unmeasured anions in the blood and to sort out acid-base and electrolyte problems. It is computed from the major measured ions as sodium minus the sum of chloride and bicarbonate. The gap roughly estimates unmeasured anions such as phosphate, sulfate, lactate, ketoacids, and some proteins. A higher than normal gap points to accumulation of these unmeasured acids, which helps detect various disease states and guide evaluation of metabolic acidosis and electrolyte disturbances. This concept is not about directly measuring chloride or unmeasured anions, and it does not diagnose liver disease; rather, it serves as a practical tool to recognize when abnormal acids are present and to narrow down the possible causes.