Thiopurine Methyltransferase, RBC, Whole Blood

Thiopurine Methyltransferase, RBC

Order Code:	TPMT
Epic Lab Code:	LAB4153
Order Form:	A-1a Miscellaneous Request or Epic Req

Commercial Mail-out Laboratory
6240 RCP
356-3527

Specimen:

Whole Blood

Collection Medium:

Green top tube 10 mL (Na Heparin)

Minimum:

5.0 mL whole blood

Rejection Criteria:

Samples not refrigerated. Samples greater than 6 days.

Analytic Time:

3-5 days upon receipt at reference laboratory.

Reference Range:

>17.0 U/mL RBC (normal) 15.4-17.0 U/mL RBC (probable low normal) 11.9-15.3 U/mL RBC (possible carrier) 6.0-11.8 U/mL RBC (carrier range) 0.0-5.9 U/mL RBC (homozygous deficient range) Reference values apply to all ages.

Interpretive Data:

Expected values for individuals in the carrier range for thiopurine methyltransferase deficiency are between 6.0 U/mL RBC to 11.8 U/mL RBC.

Expected values for individuals homozygous for deleterious mutations in the TPMT gene (deficient TPMT) are < or =5.9 U/mL RBC.

Results between 11.9 U/mL RBC and 17.0 U/mL RBC are considered ambiguous: 15.4 U/mL RBC to 17.0 U/mL RBC represents probable low normal; 11.9 U/mL RBC to 15.3 U/mL RBC represents possible carrier status.

Comments:

Useful for:
Detection of individuals with low thiopurine methyltransferase activity who are at risk for excessive myelosuppression or severe hematopoietic toxicity when taking azathioprine (Imuran) or 6-MP (Purinethol).

Methodology:

Enzymatic End-Point/Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS)

CPT Code:

83789