Pseudohyperbicarbonatemia on Chemistry Panels Due to Lactate Dehydrogenase (LDH) Interference

Introduction: Discrepancies between bicarbonate concentrations (HCO3-) measured on basic metabolic panels and those calculated via blood gas analysis have wide ranging clinical implications. It is known that triglycerides and paraproteins can interfere with measurement of the serum bicarbonate and cause inaccurate results. Here, we present eight cases of pseudo-hyperbicarbonatemia in the setting of significant LDH elevation. Case Description: We identified patient cases in which paired BMP and blood gas HCO3- levels were available and demonstrated discrepancies in HCO3- ≥5 mmol/L. The chemistry analyzer used in our institution (Beckman Coulter AU5800) measures bicarbonate through an NADH-coupled enzymatic reaction monitored via absorbance at 380/410 nm. High LDH levels appear to interfere with this assay, falsely elevating the measured HCO3-. The table below summarizes the representative cases. The median discrepancy was 16.8 mmol/L (range: 10.0–19.5), with some BMP values falsely falling within normal range, while true HCO3- levels were critically low. LDH level measured within 24 hours of these results were >6000 U/L in all instances. Use of a different analyzer confirmed the error in 2 cases. Clinical contexts included septic shock, cardiogenic shock, decompensated cirrhosis, severe rhabdomyolysis, lymphoma, and blast crisis. Discussion: This case series underscores the potential for significant diagnostic error due to pseudo-hyperbicarbonatemia. The blood gas HCO3- which is calculated from directly measured pH and PCO2 using the Henderson-Hasselbalch equation, is not subject to enzymatic interference. Our findings strongly suggest LDH-related interference in the enzymatic BMP assay. Clinicians should confirm the true acid base status with blood gas analysis when the BMP HCO3- level is discordant with clinical presentation, especially in patients with elevated LDH. Since this discrepancy has not been widely reported, institutional awareness of analyzer platform used and monitoring using standard QA processes should be considered when this analyzer is used.