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Test ID: TPMT    
Thiopurine Methyltransferase (TPMT), Erythrocytes

Method Description Describes how the test is performed and provides a method-specific reference

Thiopurine methyltransferase (TPMT) catalyzes the metabolism of 6-mercaptopurine to 6-methylmercaptopurine (6-MMP) in erythrocytes, utilizing S-adenosyl-L-methionine as the methyl group. The rate of formation of 6-MMP is an indication of the amount of TPMT present in a patient's red blood cell lysate. Reactions that would interfere with the specific TPMT methylation, such as nonenzymatic methylation of 6-MMP and the formation of methylthiopurines other than 6-MMP, are eliminated: Km (Michaelis constant)-appropriate substrate concentrations are employed in a batched reagent to reduce nonenzymatic methylation. Phosphate buffers are used because other buffers allow for the formation of methylthiopurines other than 6-MMP.(Lacey JM, Magera MJ, Matern D, O'Brien JF: Quantitation of 6-methylmercaptopurine for the determination of thiopurine methyltransferase; unpublished Mayo manuscript)

Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.

Monday, Wednesday through Friday; Varies

Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.

4 days (not reported on Saturday or Sunday)

Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result

6 days

Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

Processed specimen stored 1 month

Performing Laboratory Location The location of the laboratory that performs the test

Rochester