From the Guidelines
Blood is the best sample for drug monitoring as it provides the most accurate measurement of drug concentrations in the body. Specifically, serum or plasma samples are typically used for therapeutic drug monitoring (TDM) because they directly reflect the amount of drug available to interact with target tissues. For most medications requiring monitoring, blood samples should be collected at trough levels, just before the next scheduled dose, to ensure consistent interpretation 1. The timing of collection is critical, and blood samples offer advantages over urine or saliva because they reflect current active drug concentrations rather than accumulated metabolites or free fractions only.
Key Considerations for Drug Monitoring
- The choice of sample is influenced by the cost, ease of sample collection, risk of adulteration, test type, scope of drugs being tested, time frame, and indications for testing 1.
- Blood concentrations are most useful for detecting alcohol and other drug use that occurred within 2 to 12 hours of the test and are best correlated with the level of impairment and morbidity seen in emergency situations.
- Established therapeutic ranges for most medications are based on blood concentrations, making interpretation straightforward for clinical decision-making regarding dosage adjustments.
Comparison with Other Samples
- Urine testing is invasive and highly susceptible to tampering, but it is well standardized and studied, and provides a longer window of detection for some substances 1.
- Saliva and sweat testing provide similar information to blood testing but are less invasive and do not require extensive training for sample collection.
- Hair testing allows for detection of past use that has occurred over an extended time, but it is not useful clinically because it has a long window of detection and is affected by hair structure, growth rate, melanin content, hygiene, and cosmetic treatment.
Conclusion Not Needed, Direct Answer Provided Above
The best method for drug monitoring is through blood samples, as they provide the most accurate measurement of drug concentrations in the body, allowing for precise therapeutic drug monitoring and dosage adjustments 1.
From the Research
Best Sample for Drug Monitoring
The best sample for drug monitoring can vary depending on the specific context and goals of the monitoring. Here are some options:
- Blood: Blood is a common sample used for therapeutic drug monitoring (TDM) as it provides a direct measure of the drug concentration in the bloodstream 2, 3, 4. Blood sampling can be done through venous or capillary blood collection.
- Urine: Urine is often used for detecting illicit drug use and can provide information on recent drug use 5. However, it may not be as accurate as blood sampling for TDM.
- Dried Blood Spot (DBS): DBS is a relatively new method that involves collecting a small sample of blood on a paper card, which can be easily transported and stored 3, 4, 6. DBS has been shown to be a viable option for TDM, especially for patients with limited access to healthcare facilities.
- Oral Fluid (Saliva): Oral fluid can also be used for drug monitoring, particularly for detecting current use and impairment 5.
Considerations for Choosing a Sample
When choosing a sample for drug monitoring, several factors should be considered, including:
- Sampling time: The timing of sample collection in relation to drug dose and dosage history is crucial for accurate interpretation of results 2.
- Patient characteristics: Age, weight, organ function, and concomitant drug therapy can affect drug concentrations and should be taken into account when interpreting results 2.
- Analytical methods: The choice of analytical method can impact the accuracy and reliability of results, and methods such as paper spray mass spectrometry and LC-MS/MS have been shown to be effective for TDM 3, 4.
- Practical considerations: Factors such as sample collection, transport, and storage should be considered when choosing a sample for drug monitoring 6.