Which condition is listed as a cause of a low osmolal gap?

• A. Hypoalbuminemia
• B. Hyponatremia
• C. DKA
• D. Lactic Acidosis

Answer: (A)

Osmolal gap is the difference between what we measure as serum osmolality and what we estimate from major solutes (roughly 2 Na plus glucose and BUN). Albumin and other proteins aren’t included in the calculated value, but they contribute to the actual measured osmolality. When albumin is very low (hypoalbuminemia), the measured osmolality falls because there are fewer osmotically active particles from proteins, while the calculated osmolality remains about the same. This reduces the gap, giving a low osmolal gap. In contrast, conditions that introduce extra small-solute osmoles (like alcohols or ketoacids) raise the gap, and hyponatremia, DKA, or lactic acidosis typically increase it rather than decrease it.