Z51.81 is the ICD-10-CM code for an encounter for therapeutic drug level monitoring. It is used when a patient is seen to check that a medication is at a safe, effective level, for example a blood test for a patient on warfarin, lithium, digoxin or an anti-seizure drug. ICD-10-CM instructs coders to also report a Z79 code for the long-term (current) drug therapy.
Z51.81 at a Glance
| Item | Detail |
|---|---|
| Code | Z51.81 |
| Description | Encounter for therapeutic drug level monitoring |
| Code also | Any long term (current) drug therapy (Z79.-) |
| Can be first-listed | Yes, when monitoring is the reason for the encounter |
Pairing Z51.81 With Z79 Codes
| Medication | Z79 code |
|---|---|
| Anticoagulants (e.g., warfarin) | Z79.01 |
| Aspirin | Z79.82 |
| Insulin | Z79.4 |
| Oral hypoglycemic drugs | Z79.84 |
| Systemic steroids | Z79.52 |
| Opiate analgesics | Z79.891 |
| Other long term (current) drug therapy | Z79.899 |
Example: a patient on warfarin comes in for an INR test. Code Z51.81 with Z79.01. If the provider also manages the condition being treated, such as atrial fibrillation, add that diagnosis.
Z51.81 vs Z79.899
Z51.81 describes the reason for the encounter (monitoring drug levels). Z79.899 describes a status (the patient takes a medication long term). Z79.899 can be reported on any visit where long-term drug use matters, while Z51.81 is reported only when the encounter is for monitoring.
Billing Tips
- Lab claims for drug levels usually need Z51.81 plus the Z79 code to show medical necessity.
- Do not use Z51.81 for drug screening for substance use; see our ICD-10 codes for drug screening.
- For refill-only encounters, use Z76.0 instead.
For an overview, see the ICD-10 code for medication management.
Frequently Asked Questions
What is Z51.81?
Z51.81 is the ICD-10-CM code for an encounter for therapeutic drug level monitoring.
Can Z51.81 be a primary diagnosis?
Yes. Z51.81 can be first-listed when the purpose of the encounter is drug level monitoring. Add a Z79 code for the long-term drug therapy.
What is Z79.899?
Z79.899 is other long term (current) drug therapy. It is used when no more specific Z79 code describes the medication.
Is Z51.81 used for drug screening?
No. Testing for drugs of abuse or for administrative reasons is coded differently, for example Z02.83 for a blood-drug test required for administrative purposes.
Source: ICD-10-CM Tabular List and Official Guidelines for Coding and Reporting (CDC/CMS). Always check the current code set for the date of service.
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