Pathology/Lab Coding Alert

Study this case to understand drug toxicity diagnoses.

When your lab receives a request for drug testing, the ordering diagnosis may help you understand that a test is for diagnostic rather than screening purposes.

The following case gives a picture of how an ICD-10-CM code represents why the physician is ordering a specific test.

Clinical example: The clinician orders a test for the serum level of methotrexate, a specific chemotherapeutic agent, for a patient complaining of vomiting and throat pain following a recent chemotherapy infusion that was administered per the physician’s order.

Read on to understand how the ICD-10-CM code represents the clinical situation and the reason for the lab test order.

Get Familiar With Drug Toxicity Classifications

Codes in categories T36-T65 are combination codes that identify the substance the patient took as well as the intent. The Table of Drugs and Chemicals pinpoints the correct code for a specific type of drug and a specific type of toxicity.

To know why a clinician is ordering a specific diagnostic drug test, you need to understand the types of drug toxicity represented in ICD-10:

• Adverse effect: Problem that arises after taking a drug that has been correctly prescribed and properly administered
• Poisoning: Reaction to the improper use of a medication
• Underdosing: Taking less of a medication than is prescribed
• Toxic effect: Ingestion or contact with a harmful substance

“The key to coding from the Table of Drugs and Chemicals in ICD-10-CM is understanding the differences between these definitions, knowing the difference between adverse effect, poisoning, underdosing, and toxic effect,” says Barbara J. Cobuzzi, MBA, CPC, COC, CPC-P, CPC-I, CENTC, CPCO, CMCS, of CRN Healthcare in Tinton Falls, New Jersey.

Focus Understanding of ‘Adverse Effect’

Using the clinical example, you can see from the Table of Drugs and Chemicals under “cancer chemotherapy drug regimen” in the “adverse effect” column that the ordering physician could appropriately report T45.1X6- (Adverse effect of antineoplastic and immunosuppressive drugs).

Note: Because the clinician documented that the patient received the correct drug and dosage, the clinician would not report this using any other column from the table, such as poisoning or underdosing.

Don’t Miss the Z Code

The 2023 ICD-10-CM code set expands your options in category Z79- (Long term (current) drug therapy). This code boost allows clinicians to identify the type of chemotherapy being administered to the patient. If the specific drug is documented, the clinician should now assign one of the following codes from the Z79.63- (Long term (current) use of chemotherapeutic agent) group:

• Z79.630 (Long term (current) use of alkylating agent) for chlorambucil, cisplatin, and cyclophosphamide
• Z79.631 (Long term (current) use of antimetabolite agent) for methotrexate, 5-fluorouracil, 6-mercaptopurine, and cytarabine
• Z79.632 (Long term (current) use of antitumor antibiotic) for bleomycin, doxorubicin, and mitomycin C
• Z79.633 (Long term (current) use of mitotic inhibitor) for paclitaxel, plant alkaloids, vinblastine, and vincristine
• Z79.634 (Long term (current) use of topoisomerase inhibitor) for etoposide, irinotecan, and topotecan

Note: Be on the lookout for when the Centers for Medicare & Medicaid Services (CMS) adds the Z79.63- codes to the National Coverage Determination (NCD) and Local Coverage Determination (LCD) lists and articles. “Ordering lab work to monitor patients on these newly represented medications may not be covered if reported with Z79.899 (Other long term (current) drug therapy),” cautions Halee Garner, CPC, CPMA, CCA, certified coder for Digestive Health Partners in Asheville, North Carolina.

Procedure: With a request for methotrexate serum level for a patient with Z79.631 and T45.1X6 ordering diagnoses, the lab should perform a therapeutic drug assay test, not a screening drug test, and report the service as 80204 (Methotrexate).