When should blood be collected for therapeutic drug monitoring and fasting specimens?

Blood should be collected for therapeutic drug monitoring and fasting specimens when the patient is in a basal state. This state refers to a condition where the body is in a resting metabolic state, meaning that the patient has not consumed any food or drink (except water) for a specified period, typically 8 to 12 hours before the sample collection. This fasting period is crucial as it ensures that the levels of the drug being measured reflect the body’s baseline levels, without interference from recent food intake or other metabolic processes.

Collecting blood during this basal state allows for more accurate pharmacokinetic measurements and helps determine whether a patient is within the therapeutic range for specific medications. It minimizes variables that could impact the test results, ensuring they are not skewed by food, which could alter absorption rates and drug metabolism.

Other scenarios, such as collecting blood after exercise, during eating, or immediately after medication administration, can introduce variables that distort the true pharmacological effects or concentrations in the bloodstream, thereby complicating the interpretation of test results.