A Wolf in Sheep’s Clothing: Pseudohypobicarbonatemia in a Patient With Multiple Myeloma

There are multiple methods to measure serum bicarbonate level which is crucial for diagnosis and management of acid-base disturbances. The most common method is directly measuring the total serum carbon dioxide (CO₂) concentration in a basic metabolic panel. Another method is by indirect calculation of the bicarbonate concentration via the Henderson-Hasselbalch equation using the measured pH and partial pressure of CO₂ (pCO₂) in plasma. Multiple confounders can cause discrepancies in the measured bicarbonate in each method, such as increased concentration of serum lipids or proteins, that can alter measurement assays, leading to spuriously low serum bicarbonate values. In our case, we present a patient with falsely low reported bicarbonate levels in the setting of increased paraproteins due to multiple myeloma.