A patient has a low anion gap metabolic profile (<4). Which condition is a known cause of a low anion gap?

A patient has a low anion gap metabolic profile (<4). Which condition is a known cause of a low anion gap?

• A. Hyperalbuminemia
• B. Lactic acidosis
• C. Hypoalbuminemia
• D. Uremia

Answer: (C)

The anion gap reflects unmeasured anions in the blood, with albumin being a major contributor to that pool. When albumin levels fall (hypoalbuminemia), there are fewer negative charges that aren’t measured, so the calculated gap decreases. This is why hypoalbuminemia is a known cause of a low anion gap, sometimes dropping well below the normal range. If you corrected the gap for the low albumin, the adjusted value would often be normal or higher, highlighting that the low reading is driven by reduced albumin. In contrast, conditions like lactic acidosis or uremia add unmeasured anions (lactate, phosphate, sulfate, etc.) and tend to raise the anion gap, not lower it. Hyperalbuminemia would increase the gap rather than decrease it.

The anion gap reflects unmeasured anions in the blood, with albumin being a major contributor to that pool. When albumin levels fall (hypoalbuminemia), there are fewer negative charges that aren’t measured, so the calculated gap decreases. This is why hypoalbuminemia is a known cause of a low anion gap, sometimes dropping well below the normal range. If you corrected the gap for the low albumin, the adjusted value would often be normal or higher, highlighting that the low reading is driven by reduced albumin.

In contrast, conditions like lactic acidosis or uremia add unmeasured anions (lactate, phosphate, sulfate, etc.) and tend to raise the anion gap, not lower it. Hyperalbuminemia would increase the gap rather than decrease it.