Sorted By Test Name - Mayo Medical Laboratories

TPMT
80291
Synonym(s): Pentothal
Hypnotic range: 1-5 mcg/mL
Therapeutic coma: 30-100 mcg/mL
Anesthesia: 7-130 mcg/mL
Pentobarbital
Synonym(s): Thiopental Metabolite
Peak serum concentrations of 1.2-3.1 mcg/mL were produced
0.5-2.0 hours after a 100 mg oral dose and peak serum
concentrations of 3 mcg/mL were produced 6 min. following a
100 mg IV dose. Potentially toxic at blood concentrations greater
than 10 mcg/mL.
Test Performed By: NMS Labs
3701 Welsh Road
PO Box 433A
Willow Grove, PA 19090-0437
Thiopurine Methyltransferase (TPMT), Erythrocytes
Clinical Information: Thiopurine methyltransferase (TPMT) deficiency is a condition in which
patients treated with standard doses of the immunosuppressant azathioprine (Imuran) or the antineoplastic
drug 6-mercaptopurine (6-MP, Purinethol) may develop life-threatening myelosuppression or severe
hematopoietic toxicity. The metabolic conversion of azathioprine or 6-MP to purine nucleotides and the
subsequent incorporation of these nucleotides into DNA plays an important role in both the therapeutic
efficacy and the toxicity of these drugs. A competitive catabolic route for the metabolism of thiopurines is
catalyzed by the TPMT enzyme, which inactivates them by thiomethylation. A balance must be
established between these competing metabolic pathways so that: 1) sufficient amounts of drug are
converted to the nucleotide to act as an antimetabolite and 2) the antimetabolite levels do not become so
high as to cause potentially lethal bone marrow suppression. TPMT deficiency is an autosomal recessive
condition with an incidence of approximately 1 in 300 individuals homozygous for deleterious mutations
in the TPMT gene; about 10% of the population is heterozygous carriers of TPMT mutations. Adverse
effects of azathioprine or 6-MP administration can be observed in individuals who are either homozygous
or heterozygous for TPMT deficiency. As such, knowing a patient's TPMT status prior to treatment with
azathioprine or 6-MP is important for purposes of calculating drug dosages.
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)
Interpretation: Expected values for individuals in the carrier range for thiopurine methyltransferase
(TPMT) deficiency are between 6.0 and 10.0 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
10.1 and 14.9 U/mL RBC represents probable low normal.
Reference Values:
> or =15.0 U/mL RBC (normal)
10.1-14.9 U/mL RBC (low normal)
6.0-10.0 U/mL RBC (carrier)
0.0-5.9 U/mL RBC (deficient)
Reference values apply to all ages.
Clinical References: 1. Sandborn WJ:Pharmacogenomics and IBD: TPMT and thiopurines. Inflamm
Bowel Dis 2004;10 Suppl 1:S35-S37 2. Schedel J, Godde A, Schutz E, et al: Impact of thiopurine
methyltransferase activity and 6-thioguanine nucleotide concentrations in patients with chronic
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1732