Z51.81Encounter for therapeutic drug level monitoring

Z51.81 is the ICD-10-CM diagnosis code for encounter for therapeutic drug level monitoring. It belongs to category Z51 (encounter for other aftercare and medical care), block Z40-Z53 (Encounters for other specific health care) and chapter 21 (factors influencing health status and contact with health services). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

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.

In MS-DRG v44.0, it is part of the grouping logic for DRG 949 (Aftercare with CC/MCC, relative weight 1.123) and DRG 950 (Aftercare without CC/MCC, relative weight 0.7664), in MDC 23 (Factors Influencing Health Status and Other Contacts with Health Services), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It is exempt from present-on-admission (POA) reporting, so no POA indicator is required.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as V58.83 (encounter for therapeutic drug monitoring).