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Falsely elevated vancomycin-concentration values from enzyme immunoassay leading to treatment failure
Bridger Singer1, Ryan W Stevens2, Benjamin P Westley3
1SCL Health St. Mary's Medical Center, Grand Junction, CO.
Summary
Enzyme immunoassay (EIA) testing for vancomycin may show interference, leading to falsely high serum concentrations. This vancomycin assay interference can result in treatment failure and requires confirmation with methods like high-performance liquid chromatography (HPLC).
Area of Science:
- Clinical Chemistry
- Analytical Chemistry
- Pharmacology
Background:
- Therapeutic drug monitoring (TDM) is crucial for optimizing vancomycin efficacy and safety.
- Enzyme immunoassays (EIAs) are commonly used for vancomycin TDM.
Observation:
- A patient receiving vancomycin exhibited persistently rising serum concentrations by EIA, despite no further drug administration.
- Clinical deterioration occurred despite seemingly therapeutic vancomycin levels.
- Subsequent analysis using high-performance liquid chromatography (HPLC) revealed significantly lower vancomycin concentrations and elevated protein binding.
Findings:
- The EIA method demonstrated significant interference, yielding falsely elevated vancomycin concentrations.
- HPLC confirmed true vancomycin levels were substantially lower than EIA results.
- Assay interference contributed to vancomycin treatment failure in this case.
Implications:
- This case highlights the potential for EIA interference in vancomycin monitoring.
- Confirmatory testing with methods like HPLC is essential when results are discordant with clinical presentation.
- Unidentified interfering substances can impact patient management and treatment outcomes.
