Revenue Cycle Insider

Question: A provider wants to begin azathioprine (AZA) therapy for a patient with rheumatoid arthritis and has ordered thiopurine methyltransferase (TPMT) activity testing to calculate the correct dosage of AZA to give to the patient. Should we report 82657 or 81335 for the TPMT activity test?

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Answer: Neither of those codes is an accurate way to report the test you describe. Code 82657 (Enzyme activity in blood cells, cultured cells, or tissue, not elsewhere specified; nonradioactive substrate, each specimen) was correct prior to the 2023 CPT^® code set, but the code is a nonspecific enzyme-activity test code. Since then, you have had a more specific code — 84433 (Thiopurine S-methyltransferase (TPMT)) — which, as the descriptor states, is used to test for TPMT activity. This is the correct code to use for the lab test you mention in your question.

Code 81335 (TPMT (thiopurine S-methyltransferase) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3) also specifies TPMT in its descriptor, but that code is also incorrect to use to report testing for TPMT activity. Per CPT^® Assistant April 2023 (Volume 33, Issue 4), 84433 is the correct code to report to test for TPMT activity as 81335 “describes a mutation analysis to assess a patient’s TPMT metabolizer status.” This is what the descriptor for 81335 indicates when it references gene analysis, as the test analyzes the genes responsible for low TPMT enzyme activity.

Bruce Pegg, BA, MA, CPC, CFPC, Managing Editor, AAPC