Z51.81: Encounter for therapeutic drug level monitoring
Z51.81, encounter for therapeutic drug level monitoring, is listed as a covered diagnosis in 9 Medicare billing and coding articles that apply to 32 HCPCS Level II codes, including G0480 (Drug test(s), definitive, utilizing (1) drug…), G0483 (Drug test(s), definitive, utilizing (1) drug…), G0482 (Drug test(s), definitive, utilizing (1) drug…). The articles come from 6 Medicare contractors. A listed diagnosis supports medical necessity only; coverage still depends on the LCD's criteria and on documentation in the medical record.
HCPCS Level II codes with Z51.81 as a covered diagnosis
| Code | Description | Medicare coverage | DMEPOS fee 2026 (state range) | Articles listing it |
|---|---|---|---|---|
| G0480 | Drug test(s), definitive, utilizing (1) drug identification methods able to identify individual drugs and distinguish between structural isomers (but not necessarily stereoisomers), including, but not limited to gc/ms (any type, single or tandem) and lc/ms (any type, single or tandem and excluding immunoassays (e.g., ia, eia, elisa, emit, fpia) and enzymatic methods (e.g., alcohol dehydrogenase)), (2) stable isotope or other universally recognized internal standards in all samples (e.g., to control for matrix effects, interferences and variations in signal strength), and (3) method or drug-specific calibration and matrix-matched quality control material (e.g., to control for instrument variations and mass spectral drift); qualitative or quantitative, all sources, includes specimen validity testing, per day; 1-7 drug class(es), including metabolite(s) if performed | Carrier judgment | — | 6 |
| G0483 | Drug test(s), definitive, utilizing (1) drug identification methods able to identify individual drugs and distinguish between structural isomers (but not necessarily stereoisomers), including, but not limited to gc/ms (any type, single or tandem) and lc/ms (any type, single or tandem and excluding immunoassays (e.g., ia, eia, elisa, emit, fpia) and enzymatic methods (e.g., alcohol dehydrogenase)), (2) stable isotope or other universally recognized internal standards in all samples (e.g., to control for matrix effects, interferences and variations in signal strength), and (3) method or drug-specific calibration and matrix-matched quality control material (e.g., to control for instrument variations and mass spectral drift); qualitative or quantitative, all sources, includes specimen validity testing, per day; 22 or more drug class(es), including metabolite(s) if performed | Carrier judgment | — | 6 |
| G0482 | Drug test(s), definitive, utilizing (1) drug identification methods able to identify individual drugs and distinguish between structural isomers (but not necessarily stereoisomers), including, but not limited to gc/ms (any type, single or tandem) and lc/ms (any type, single or tandem and excluding immunoassays (e.g., ia, eia, elisa, emit, fpia) and enzymatic methods (e.g., alcohol dehydrogenase)), (2) stable isotope or other universally recognized internal standards in all samples (e.g., to control for matrix effects, interferences and variations in signal strength), and (3) method or drug-specific calibration and matrix-matched quality control material (e.g., to control for instrument variations and mass spectral drift); qualitative or quantitative, all sources, includes specimen validity testing, per day; 15-21 drug class(es), including metabolite(s) if performed | Carrier judgment | — | 6 |
| G0481 | Drug test(s), definitive, utilizing (1) drug identification methods able to identify individual drugs and distinguish between structural isomers (but not necessarily stereoisomers), including, but not limited to gc/ms (any type, single or tandem) and lc/ms (any type, single or tandem and excluding immunoassays (e.g., ia, eia, elisa, emit, fpia) and enzymatic methods (e.g., alcohol dehydrogenase)), (2) stable isotope or other universally recognized internal standards in all samples (e.g., to control for matrix effects, interferences and variations in signal strength), and (3) method or drug-specific calibration and matrix-matched quality control material (e.g., to control for instrument variations and mass spectral drift); qualitative or quantitative, all sources, includes specimen validity testing, per day; 8-14 drug class(es), including metabolite(s) if performed | Carrier judgment | — | 6 |
| G0659 | Drug test(s), definitive, utilizing drug identification methods able to identify individual drugs and distinguish between structural isomers (but not necessarily stereoisomers), including but not limited to gc/ms (any type, single or tandem) and lc/ms (any type, single or tandem), excluding immunoassays (e.g., ia, eia, elisa, emit, fpia) and enzymatic methods (e.g., alcohol dehydrogenase), performed without method or drug-specific calibration, without matrix-matched quality control material, or without use of stable isotope or other universally recognized internal standard(s) for each drug, drug metabolite or drug class per specimen; qualitative or quantitative, all sources, includes specimen validity testing, per day, any number of drug classes | Carrier judgment | — | 6 |
| A9500 | Technetium tc-99m sestamibi, diagnostic, per study dose | Carrier judgment | — | 2 |
| A9502 | Technetium tc-99m tetrofosmin, diagnostic, per study dose | Carrier judgment | — | 2 |
| A9505 | Thallium tl-201 thallous chloride, diagnostic, per millicurie | Carrier judgment | — | 2 |
| A9512 | Technetium tc-99m pertechnetate, diagnostic, per millicurie | Carrier judgment | — | 2 |
| A9560 | Technetium tc-99m labeled red blood cells, diagnostic, per study dose, up to 30 millicuries | Carrier judgment | — | 2 |
| A9538 | Technetium tc-99m pyrophosphate, diagnostic, per study dose, up to 25 millicuries | Carrier judgment | — | 2 |
| A9501 | Technetium tc-99m teboroxime, diagnostic, per study dose | Carrier judgment | — | 2 |
| J2785 | Injection, regadenoson, 0.1 mg | Carrier judgment | — | 2 |
| J0153 | Injection, adenosine, 1 mg (not to be used to report any adenosine phosphate compounds) | Special coverage instructions apply | — | 2 |
| J1250 | Injection, dobutamine hydrochloride, per 250 mg | Special coverage instructions apply | — | 2 |
| J1245 | Injection, dipyridamole, per 10 mg | Special coverage instructions apply | — | 2 |
| J3490 | Unclassified drugs | Special coverage instructions apply | — | 1 |
| A9520 | Technetium tc-99m tilmanocept, diagnostic, up to 0.5 millicuries | Carrier judgment | — | 1 |
| C9176 | Tc-99m from domestically produced non-heu mo-99, [minimum 50 percent], full cost recovery add-on, per study dose | Special coverage instructions apply | — | 1 |
| J0461 | Injection, atropine sulfate, 0.01 mg | Special coverage instructions apply | — | 1 |
| Q9957 | Injection, perflutren lipid microspheres, per ml | Carrier judgment | — | 1 |
| J0280 | Injection, aminophyllin, up to 250 mg | Special coverage instructions apply | — | 1 |
| Q9956 | Injection, octafluoropropane microspheres, per ml | Carrier judgment | — | 1 |
| A9700 | Supply of injectable contrast material for use in echocardiography, per study | Special coverage instructions apply | — | 1 |
| C8921 | Transthoracic echocardiography with contrast, or without contrast followed by with contrast, for congenital cardiac anomalies; complete | Special coverage instructions apply | — | 1 |
7 more codes are listed. See every code with payment by region in Caduvo.
Medicare policy articles listing Z51.81
- A56494: Billing and Coding: Cardiovascular Nuclear Medicine (CGS Administrators, LLC (MAC - Part A, MAC - Part B); 12 Level II codes). LCD with the same title: L33560, L33960
- A56743: Billing and Coding: Cardiovascular Nuclear Medicine (Wellpoint Federal (MAC - Part A, MAC - Part B); 9 Level II codes). LCD with the same title: L33560, L33960
- A57077: Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing (First Coast Service Options, Inc. (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L35006, L36393
- A55001: Billing and Coding: Urine Drug Testing (Noridian Healthcare Solutions, LLC (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L34645, L35724, L36029, L36668
- A56915: Billing and Coding: Urine Drug Testing (WPS Insurance Corporation (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L34645, L35724, L36029, L36668
- A59416: Billing and Coding: Urine Drug Testing (Wellpoint Federal (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L34645, L35724, L36029, L36668
- A54799: Billing and Coding: Urine Drug Testing (Palmetto GBA (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L34645, L35724, L36029, L36668
- A56818: Billing and Coding: Urine Drug Testing (CGS Administrators, LLC (MAC - Part A, MAC - Part B); 5 Level II codes). LCD with the same title: L34645, L35724, L36029, L36668
- A56781: Billing and Coding: Transthoracic Echocardiography (TTE) (Wellpoint Federal (MAC - Part A, MAC - Part B); 17 Level II codes). LCD with the same title: L33577, L34338
A diagnosis listed as covered in a billing and coding article supports medical necessity for the article's codes; it does not guarantee payment. Coverage depends on the LCD's criteria, the contractor's jurisdiction and documentation in the medical record.
Other Z51 diagnoses (Encounter for other aftercare and medical care)
- Z51.89 — Encounter for other specified aftercare
- Z51.11 — Encounter for antineoplastic chemotherapy
- Z51.12 — Encounter for antineoplastic immunotherapy
Frequently asked questions
Does Medicare cover Z51.81 (Encounter for therapeutic drug level monitoring)?
Medicare covers items and services, not diagnoses. 9 Medicare billing and coding articles list Z51.81 as a covered diagnosis for 32 HCPCS Level II codes: the diagnosis can support medical necessity for those codes, but payment still depends on the LCD's coverage criteria and the medical record.
Which HCPCS codes can be billed with ICD-10 Z51.81?
The Level II codes from the policies most specific to this diagnosis are G0480 (Drug test(s), definitive, utilizing (1) drug…, 6 articles); G0483 (Drug test(s), definitive, utilizing (1) drug…, 6 articles); G0482 (Drug test(s), definitive, utilizing (1) drug…, 6 articles); G0481 (Drug test(s), definitive, utilizing (1) drug…, 6 articles); G0659 (Drug test(s), definitive, utilizing drug identification…, 6 articles). Code choice depends on the item supplied; check each code's descriptor.
Which Medicare policy articles list Z51.81?
A56494 (Billing and Coding: Cardiovascular Nuclear Medicine); A56743 (Billing and Coding: Cardiovascular Nuclear Medicine); A57077 (Billing and Coding: Controlled Substance Monitoring and Drugs of Abuse Testing), and 6 more articles.
What is ICD-10-CM code Z51.81?
Z51.81 is the ICD-10-CM code for encounter for therapeutic drug level monitoring, in category Z51 (Encounter for other aftercare and medical care), chapter 22: Factors influencing health status and contact with health services.
Next steps
- Run a reimbursement report for a device billed under G0480
- Watch G0480 for fee, coverage and descriptor changes
- Build a full Medicare revenue model for G0480
Sources: CMS Medicare Coverage Database billing and coding articles (covered ICD-10 code lists and HCPCS links); ICD-10-CM FY2026; CMS HCPCS Level II release October 2026; CMS DMEPOS fee schedule 2026 (non-rural state fees). Not billing or legal advice.
Chapter 22: Factors influencing health status and contact with health services · All diagnoses · HCPCS lookup