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Thiopurine S-methyltransferase (TPMT) is a critical enzyme involved in the metabolism of thiopurine drugs, which are cytotoxic agents commonly used in the treatment of conditions such as leukemia and inflammatory bowel disease. These drugs function by suppressing the immune system, making the assessment of TPMT activity essential prior to initiating treatment. The CPT® code 84433 specifically refers to the laboratory test that measures the activity of TPMT in red blood cells. This blood test is particularly important for identifying patients who may have low or intermediate levels of TPMT activity, as these levels can significantly influence the safety and efficacy of thiopurine therapy. When a patient has low TPMT activity, there is a heightened risk of severe bone marrow toxicity, which can lead to myelosuppression—a potentially life-threatening condition characterized by a decrease in the production of blood cells. Consequently, if a patient is found to have low TPMT activity, it is recommended that thiopurine treatment be avoided altogether. On the other hand, patients with intermediate TPMT activity may still be candidates for thiopurine therapy, but they will require careful dose adjustments and close monitoring to mitigate the risk of adverse effects. The testing for TPMT enzymatic activity is performed using advanced techniques such as quantitative liquid chromatography-tandem mass spectrometry, ensuring accurate and reliable results that guide clinical decision-making in the management of patients requiring thiopurine medications.
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The thiopurine S-methyltransferase (TPMT) test, represented by CPT® code 84433, is indicated for patients who are being considered for thiopurine therapy. The following conditions and scenarios warrant the performance of this test:
The procedure for testing TPMT activity involves several key steps that ensure accurate measurement of the enzyme's levels in the patient's blood. The following outlines the procedural steps:
After the TPMT test is completed, the results will guide clinical decisions regarding the initiation of thiopurine therapy. If the test indicates low TPMT activity, healthcare providers will typically advise against the use of thiopurines due to the high risk of myelosuppression. In cases where intermediate TPMT activity is detected, a dose reduction of thiopurine medications will be necessary, along with close monitoring of the patient’s response to treatment. It is crucial for healthcare providers to communicate the test results to the patient and discuss the implications for their treatment plan, ensuring that any necessary adjustments are made to optimize safety and efficacy.
| Short Descr | ASY THIOPURIN S-MTHYLTRNSFRS | Medium Descr | ASSAY THIOPURINE S-METHYLTRANSFERASE | Long Descr | Thiopurine S-methyltransferase (TPMT) | Status Code | Statutory Exclusion (from MPFS, may be paid under other methodologies) | Global Days | XXX - Global Concept Does Not Apply | PC/TC Indicator (26, TC) | 9 - Not Applicable | Multiple Procedures (51) | 9 - Concept does not apply. | Bilateral Surgery (50) | 9 - Concept does not apply. | Physician Supervisions | 09 - Concept does not apply. | Assistant Surgeon (80, 82) | 9 - Concept does not apply. | Co-Surgeons (62) | 9 - Concept does not apply. | Team Surgery (66) | 9 - Concept does not apply. | Diagnostic Imaging Family | 99 - Concept Does Not Apply | CLIA Waived (QW) | No | APC Status Indicator | Conditionally packaged laboratory tests | Type of Service (TOS) | 5 - Diagnostic Laboratory | Berenson-Eggers TOS (BETOS) | none | MUE | 1 |
| 90 | Reference (outside) laboratory: when laboratory procedures are performed by a party other than the treating or reporting physician or other qualified health care professional, the procedure may be identified by adding modifier 90 to the usual procedure number. | 26 | Professional component: certain procedures are a combination of a physician or other qualified health care professional component and a technical component. when the physician or other qualified health care professional component is reported separately, the service may be identified by adding modifier 26 to the usual procedure number. | X5 | Diagnostic services requested by another clinician: for reporting services by a clinician who furnishes care to the patient only as requested by another clinician or subsequent and related services requested by another clinician; this modifier is reported for patient relationships that may not be adequately captured by the above alternative categories; reporting clinician service examples include but are not limited to, the radiologist's interpretation of an imaging study requested by another clinician |
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| 2023-01-01 | Added | Code added. |
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