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Discordant results from "real-world" patient samples assayed for digoxin
Terry E Jones1, Raymond G Morris
1Department of Pharmacy, The Queen Elizabeth Hospital, Woodville, South Australia. terry.jones@nwahs.sa.gov.au
The Annals of Pharmacotherapy
|November 27, 2008
Summary
Commercial digoxin immunoassays often yield significantly different results, impacting patient care. An equation-based estimate is not a reliable alternative for therapeutic drug monitoring.
Area of Science:
- Clinical Chemistry
- Pharmacology
- Analytical Chemistry
Background:
- Digoxin, a medication with a narrow therapeutic index, requires precise dosing.
- Therapeutic drug monitoring (TDM) is crucial for optimizing digoxin therapy.
- Existing digoxin immunoassays exhibit cross-reactivity issues, potentially affecting accuracy.
Purpose of the Study:
- To evaluate clinical discordance between different digoxin immunoassays using real-world patient samples.
- To determine the frequency of clinically significant discordant results.
- To compare immunoassay results with an equation-based digoxin concentration estimate.
Main Methods:
- Simultaneous analysis of plasma samples using two accredited laboratories and distinct digoxin immunoassays (Cedia DRI and DGNA).
- Comparison of immunoassay results against an equation-based plasma digoxin concentration estimate.
- Assessment of interassay concordance and variability.
Main Results:
- Significant discordance in digoxin concentrations was observed in 39% of samples, potentially leading to incorrect dosage adjustments.
- Digoxin-like immunoreactive substances may contribute to assay variability.
- While the mean equation-based estimate was comparable, individual results showed marked variability compared to immunoassays.
Conclusions:
- Commercial digoxin immunoassays frequently yield clinically significant discordant results.
- Equation-based estimates are not a suitable substitute for digoxin therapeutic drug monitoring.
- Assay manufacturers need to improve performance with real-world samples; clinicians must interpret digoxin assay results cautiously.
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