A trough vancomycin level drawn at 1430h after a 1400h dose is reported as 27 mg/L and exceeds the therapeutic range. What should be done?

• A. The trough dose was collected after the 1400h dose resulting in a falsely elevated level reflecting a post-dose peak, reject the specimen
• B. A trough taken before the 1400h dose should be used for interpretation
• C. The result is valid and no action is needed
• D. The patient should have a dose adjustment based on the value without retesting

Answer: (A)

In vancomycin monitoring, the trough level is meant to reflect the lowest concentration just before the next dose. If the sample is drawn after giving a dose, it captures the drug’s concentration while the body is still in the post-dose phase, which is typically higher than the true trough. That makes the result falsely elevated and not useful for guiding dosing.

Therefore this specimen should be rejected as a trough and a new trough should be collected in the appropriate pre-dose window before the next scheduled dose. Do not base dose adjustments on this post-dose value, and do not interpret it as a valid trough.

If a valid trough is obtained later, use that value to guide any dose changes.