THIOPURINE METHYLTRANSFERASE, ERYTHROCYTES

Code
000.0000
Name
THIOPURINE METHYLTRANSFERASE, ERYTHROCYTES
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
TPMT
CPT Codes
82657
Site
SBMF
Reference Test
44808
ATLAS Test Code

Specimen Information

Type

Lavender top (EDTA), WHOLE BLOOD

Volume

5.0 ml

Transport Info

Refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

See Report

Methodology

Enzymatic
High Performance Liquid Chromatography (HPLC)

Clinical Significance

The TPMT, RBC assay is used as a screen to detect individuals with low (abnormal) TPMT activity that may be at risk for excessive myelosuppression when exposed to standard doses of thiopurines such as azathioprine (Imuran) and 6-mercaptopurine (Purinethol). TPMT is the primary metabolic route for inactivation of thiopurine drugs in the bone marrow. When TPMT activity is low, it is predicted that proportionately more 6-mercaptopurine is converted into the cytotoxic 6-thioguanine nucleotides, which will accumulate in the bone marrow and cause excessive toxicity. The activity of TPMT is measured by the nanomoles of 6-methylmercaptopurine (inactive metabolite) produced per 1 mL of packed red blood cells, (U/mL).

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