Precision of digoxin radioimmunoassays and matrix effects: four kits compared
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Sample matrix interference affects digoxin radioimmunoassays. Different patient conditions, like spironolactone use or uremia, caused significant digoxin measurement errors, impacting clinical accuracy.
Area of Science:
- Clinical Chemistry
- Analytical Chemistry
- Pharmacokinetics
Background:
- Accurate digoxin measurement is crucial for therapeutic drug monitoring.
- Radioimmunoassays are commonly used for digoxin quantification.
- Potential interference from patient sample matrices can affect assay accuracy.
Purpose of the Study:
- To investigate the impact of sample matrix interference on digoxin radioimmunoassays.
- To evaluate the performance of four commercial digoxin immunoassay kits.
- To assess digoxin measurement accuracy in plasma from patients with specific conditions.
Main Methods:
- Four commercial digoxin radioimmunoassay kits were used.
- Plasma samples from non-digitalized patients with essential hypertension (on spironolactone), uremia, and acute myocardial infarction (AMI) were analyzed.
- A known concentration of digoxin (2.50 nmol/L) was added to all samples for interference assessment.
Main Results:
- Two kits overestimated digoxin in spironolactone-treated patients (p<0.01).
- One kit underestimated digoxin in uremic patients (p<0.01).
- One kit overestimated digoxin in AMI patients (p<0.05).
- Significant inter-assay and intra-assay variations were observed.
Conclusions:
- Sample matrix significantly interferes with digoxin radioimmunoassays, leading to inaccurate measurements.
- Assay performance varied considerably between different commercial kits and patient sample types.
- Despite matrix effects, the overall low precision of the assays made these deviations secondary.
Abstract:
We studied the interference of the sample matrix on digoxin radioimmunoassays using four commercial kits. Plasma samples from non-digitalized patients of the following categories were assayed: uncomplicated essential hypertension treated with spironolactone, uremia, and acute myocardial infarction (AMI). Digoxin 2.50 nmol/L was added to all samples. Digoxin in plasma from patients on spironolactone was overestimated by two of the kits (means 2.77 and 2.68 nmol/L, respectively; p less than 0.01) and underestimated in samples from uremic patients by one kit (2.32 nmol/L; p less than 0.01). The digoxin content of AMI plasma was overestimated by one kit (2.62 nmol/L; p less than 0.05). Significant differences were found between radioimmunoassays when estimating digoxin concentration in the same category of patient and within individual methods used for different categories. Precision expressed as 95% confidence intervals ranged from 0.43 to 0.80 nmol/L for the kits. Thus, deviations in recorded digoxin concentrations from the true values found, but were of secondary importance because of the relatively low precision of the assays.