Artifactually elevated serum bicarbonate results caused by elevated serum lactate dehydrogenase concentrations.

Background: An accurate estimation of serum bicarbonate concentration (HCO3(-)) is essential to the diagnosis and treatment of acid-base disorders and electrolyte disturbances. We noted significant discrepancies between HCO3(-) concentration measured by the Olympus AU2700 analyser and total serum carbon dioxide (TCO2) concentration derived from a Radiometer blood gas analyser on several patient samples. This was reported to the manufacturer which led to a recall of certain reagent lot numbers. We hypothesised the mechanism for this interference to be elevated levels of lactate dehyrogenase (LD).

Methods: We investigated the effect of increasing LD concentration on HCO3(-) with the reagent lot that was recalled and compared this with a subsequent reagent lot that was known to be unaffected on an Olympus AU2700.

Results: The experimental data confirmed a positive interference in the Olympus AU2700 HCO3(-) assay using older reagent lot numbers. The false positive HCO3(-) interference was significant (>10% change) when the LD concentration exceeded 845 U/L.

Conclusions: Very high levels of LD concentrations were the cause of interference in the Olympus AU2700 HCO3(-) enzymatic assay. Laboratorians should be aware that very high levels of LD may be a potential interference in some enzymatic HCO3(-) assays.