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Operator error: a critical determinant of false amikacin and tobramycin concentrations using fluorescence
S K Banerjee1, A Wells, A Dasgupta
1Department of Pathology and Laboratory Medicine, University of Texas-Houston Medical School, 77030, USA.
Abstract:
Amikacin and tobramycin are aminoglycosides used to treat severe Gram-negative infections. Therapeutic monitoring of both drugs is essential to avoid drug toxicity. Fluorescence polarization immunoassay kits for both amikacin and tobramycin are available from Abbott Laboratories, and assays can be run using the TDx analyzer. The test code for amikacin is 3, whereas the test code for tobramycin is 2. Here the authors report that when the operator mistakenly programmed test code 3 (amikacin code) while using the tobramycin kit, the tobramycin values were falsely elevated. The instrument software does not have any mechanism to detect this error. Similarly, when the amikacin kit was used and the operator mistakenly programmed test code 2 (tobramycin code), the amikacin values were falsely lowered. For example, in a serum sample taken from a patient the true amikacin concentration was 20.9 microg/mL. When the amikacin kit was used correctly but test code 2 was programmed, the observed concentration was falsely lowered to 6.1 microg/mL. Similarly, in another specimen the true tobramycin concentration was 3.1 microg/mL. However, when the tobramycin kit was used correctly but test code 3 was used, the observed concentration was falsely elevated to 14.3 microg/mL. The authors also observed a similar effect with controls and spiked specimens containing either amikacin or tobramycin. They conclude that correct programming of the test code is vital to obtaining useful results in amikacin and tobramycin analysis using the TDx analyzer.
Insights
Incorrect programming of test codes for amikacin and tobramycin assays on the TDx analyzer can lead to falsely inaccurate drug levels. Ensuring correct test code selection is crucial for reliable therapeutic drug monitoring.
Area of Science:
- Clinical Chemistry
- Pharmacology
- Medical Diagnostics
Background:
- Amikacin and tobramycin are critical aminoglycoside antibiotics for severe Gram-negative infections.
- Therapeutic drug monitoring (TDM) is essential to optimize efficacy and minimize toxicity of these agents.
- Fluorescence polarization immunoassays (FPIAs) are commonly used for TDM of amikacin and tobramycin.
Purpose of the Study:
- To investigate the impact of incorrect test code programming on amikacin and tobramycin measurements using Abbott Laboratories' FPIA kits on the TDx analyzer.
- To highlight potential sources of error in TDM and emphasize the need for accurate test code selection.
Main Methods:
- Utilized Abbott Laboratories' FPIA kits for amikacin (test code 3) and tobramycin (test code 2) on the TDx analyzer.
- Intentionally programmed incorrect test codes with corresponding drug kits using patient serum, controls, and spiked specimens.
- Compared measured drug concentrations against true concentrations to assess the effect of programming errors.
Main Results:
- Programming the amikacin test code (3) with the tobramycin kit resulted in falsely elevated tobramycin values.
- Programming the tobramycin test code (2) with the amikacin kit resulted in falsely lowered amikacin values.
- Significant discrepancies were observed, e.g., a true amikacin level of 20.9 µg/mL measured as 6.1 µg/mL, and a true tobramycin level of 3.1 µg/mL measured as 14.3 µg/mL.
Conclusions:
- The TDx analyzer software lacks a mechanism to detect or flag incorrect test code programming errors.
- Accurate programming of the test code is critically important for obtaining clinically meaningful results in amikacin and tobramycin TDM.
- Clinicians and laboratory personnel must exercise vigilance to ensure correct test code selection to avoid erroneous drug level reporting.