From the Research
A low anion gap (less than 3-5 mEq/L) is primarily caused by hypoalbuminemia, as albumin is negatively charged and contributes significantly to the anion gap, and other important causes include paraproteinemias, lithium toxicity, severe hypercalcemia or hypermagnesemia, bromide intoxication, and polymyxin B therapy. When evaluating a low anion gap, it is essential to consider the potential causes and their implications for patient management. The most recent and highest quality study, 1, provides a practical approach to evaluating a low anion gap, emphasizing the importance of considering various causes, including hypoalbuminemia, paraproteinemias, and lithium toxicity. Key points to consider when evaluating a low anion gap include:
- Hypoalbuminemia: a decrease in albumin levels can lower the anion gap, with each 1 g/dL decrease in albumin resulting in a decrease of approximately 2.5 mEq/L in the anion gap
- Paraproteinemias: abnormal proteins, such as those seen in multiple myeloma or Waldenström's macroglobulinemia, can carry positive charges that neutralize negative charges, leading to a low anion gap
- Lithium toxicity: the positive charge of lithium ions can contribute to a low anion gap
- Severe hypercalcemia or hypermagnesemia: these conditions can contribute positive charges that lower the anion gap
- Bromide intoxication: laboratory interference can artificially lower the measured anion gap
- Polymyxin B therapy: this medication can also reduce the anion gap It is crucial to consider these potential causes and evaluate the patient's clinical presentation, laboratory results, and medical history to determine the underlying cause of the low anion gap, as noted in 2, 3, and 4. By taking a systematic approach to evaluating a low anion gap, clinicians can provide timely and effective management, improving patient outcomes and reducing morbidity and mortality.