From the Research
A low anion gap is primarily caused by hypoalbuminemia, which is the most common cause, and other factors such as paraproteinemias, lithium or bromide intoxication, and laboratory error, as supported by the most recent study 1. When evaluating a low anion gap, it's essential to consider the following key points:
- Hypoalbuminemia, where decreased albumin reduces the measured anion gap, is a primary cause, with each 1 g/dL decrease in albumin decreasing the anion gap by approximately 2.5 mEq/L 2.
- Paraproteinemias, such as multiple myeloma, can cause a low anion gap due to abnormal proteins carrying positive charges that neutralize anions 3.
- Lithium or bromide intoxication can also contribute to a low anion gap, as these cations are measured with sodium but not accounted for in the anion gap calculation 4.
- Laboratory error, severe hypernatremia, hypercalcemia, and hypermagnesemia can also affect the anion gap by altering the balance of unmeasured ions 5.
- Conditions causing increased levels of positively charged proteins, such as polyclonal gammopathy, can similarly lower the anion gap 2. It is crucial to check albumin levels and consider medication history, particularly lithium use, as well as screening for paraproteins if clinically indicated, to accurately diagnose and manage a low anion gap 1.