The trough level is the lowest concentration in the patient’s bloodstream, therefore, the specimen should be collected just prior to administration of the drug. The peak level is the highest concentration of a drug in the patient’s bloodstream.

What is a trough test?

A trough level is drawn immediately before the next dose of the drug is administered. A peak level is drawn 1 to several hours after the drug is administered (depending on the drug).

What do peak and trough indicate?

Peak and trough levels indicate drug levels in an individual’s body. A peak is the highest level of a medication in the blood, while a trough level indicates the lowest concentration. Troughs of medication concentration occur after the drug has been broken down and metabolized by the body.