ICD-10-CM 2027
ICD-10 code for therapeutic drug level monitoring
From the official ICD-10-CM alphabetic index entry “Monitoring (encounter for) › therapeutic drug level”. Page updated September 29, 2026.
About coding therapeutic drug level monitoring
The ICD-10-CM code for therapeutic drug level monitoring is Z51.81 (Encounter for therapeutic drug level monitoring).
Within Z51.8 (encounter for other specified aftercare), Z51.81 is specifically for encounter for therapeutic drug level monitoring. Related codes cover other specified aftercare (Z51.89).
Don't report Z51.81 together with the conditions in its Excludes1 note: encounter for blood-drug test for administrative or medicolegal reasons (Z02.83).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
Don't confuse with (Excludes1 for Z51.81)
- encounter for blood-drug test for administrative or medicolegal reasons (Z02.83)
Common questions about therapeutic drug level monitoring ICD-10 codes
What is the ICD-10 code for therapeutic drug level monitoring?
- Z51.81 — Encounter for therapeutic drug level monitoring.
Is Z51.81 billable?
- Yes. Z51.81 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can Z51.81 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict Z51.81 as a principal diagnosis.
Is Z51.81 a CC or MCC?
- No. Z51.81 is neither a CC nor an MCC under MS-DRG v44.0.