The Lactate Dehydrogenase (LDH) Mirage: Falsely Elevated Serum Bicarbonate Caused by Severe LDH Elevation

Introduction: Accurate serum bicarbonate (HCO3-) measurement is essential for evaluating acid-base disorders. Elevated LDH (>845 U/L) has been shown to cause >10% positive interference in the Olympus AU2700 enzymatic assay, producing falsely elevated bicarbonate values. Case Description: A 30-year-old male with metastatic testicular cancer status-post radiation and chemotherapy presented to the hospital with lower back pain. On admission, he was found to have L2–L5 spinal metastases requiring spinal tumor resection. Labs showed rising creatinine from 0.95 mg/dL to 1.26 mg/dL by hospital day 19. Concurrently, serum bicarbonate increased from 39 to 47 mEq/L, with potassium of 5.5 mEq/L. Arterial blood gas on day 19 showed pH 7.37, pCO2 44 mm Hg, and calculated bicarbonate 25 mEq/L—arguing against true metabolic alkalosis. LDH rose from 3,126 to 8,935 U/L in parallel with the bicarbonate increase, suggesting analytical interference. Discussion: This case demonstrates pseudohyperbicarbonatemia due to LDH interference with enzymatic bicarbonate assays. LDH, absorbing at 340 nm, can artifactually elevate HCO3- values. Interference above 845 U/L has prompted reagent recalls. Similar artifacts are reported in hyperlipidemia and paraproteinemia. When bicarbonate is discordant with clinical findings, confirmation via ABG or ion-selective electrode is warranted, especially with marked LDH elevation.Dual-axis plot showing a temporal association between serum LDH and apparent bicarbonate levels.