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The reliability of serum theophylline determinations from clinical laboratories
Abstract:
Three aliquots of pooled serum containing theophylline and disguised as patient specimens were sent, one at a time, on different days, to 29 community hospital and referral laboratories serving Iowa. The mean +/- SEM concentration of 65 replications for the same serum pool was 15.7 +/- 0.1 microgram/ml. Twenty-eight per cent of the 85 measurements reported by the clinical laboratories were outside the acceptable range of 13.2 to 18.1 microgram/ml established by the 95% confidence limits of the assayed pool. Reliability of the results was not related to the type of facility, method of measurement, or fee charged. Therefore, variation in clinical laboratory performance was a result of technician error in handling or analyzing the specimens. We conclude that measurements of serum theophylline can only be relied on to adjust dosage when the accuracy of the laboratory has been established with blinded samples.
Insights
Clinical laboratory measurements of theophylline serum concentrations can be unreliable. Accuracy is crucial for dosage adjustments, necessitating laboratory validation with blinded samples to ensure dependable patient care.
Area of Science:
- Clinical Chemistry
- Pharmacokinetics
- Laboratory Medicine
Background:
- Theophylline is a critical medication requiring precise serum concentration monitoring for therapeutic efficacy and safety.
- Variability in clinical laboratory testing can impact patient treatment and outcomes.
Purpose of the Study:
- To assess the accuracy and reliability of theophylline serum concentration measurements across diverse clinical laboratories.
- To identify factors contributing to measurement variability in routine laboratory settings.
Main Methods:
- Blind proficiency testing using pooled serum samples containing theophylline.
- Distribution of samples to 29 community hospital and referral laboratories.
- Analysis of reported theophylline concentrations against established acceptable ranges.
Main Results:
- Twenty-eight percent of reported measurements fell outside the acceptable range (13.2-18.1 microgram/ml).
- No correlation was found between accuracy and laboratory type, measurement method, or cost.
- Observed performance variations were attributed to technician-related errors in specimen handling and analysis.
Conclusions:
- Clinical laboratory performance in measuring serum theophylline concentrations exhibits significant variability.
- Reliable theophylline dosage adjustments depend on a laboratory's demonstrated accuracy, confirmed via blinded sample analysis.
- Implementing quality control measures, including the use of blinded samples, is essential for ensuring the reliability of therapeutic drug monitoring.