Pseudohypobicarbonatemia in a patient with amyloidosis.

We report a case of a patient who had critically low serum bicarbonate (HCO3 -) levels ranging from 8 to 11 mmol/L on repeated venous measurements using an enzymatic/photometric assay. This prompted hospitalization and treatment with intravenous sodium bicarbonate (NaHCO3) followed by oral NaHCO3. He was evaluated for potential causes of high anion gap metabolic acidosis without any etiology found. He continued to have low serum HCO3 - levels despite maintenance oral NaHCO3 therapy and was referred for a second opinion where further laboratory work was pursued. An arterial blood gas was obtained, which revealed normal whole blood pH and HCO3 - levels. A different enzymatic/photometric assay revealed a normal serum HCO3 - level at 21 mmol/L. Additional workup revealed paraproteinemia, which was thought to interfere with the enzymatic process by which his serum HCO3 - was measured, resulting in erroneous values.