What is the TPMT enzyme blood test for?

Though the TPMT test is used to predict risk of bone marrow toxicity, complete blood counts (CBCs) should also be done at regular intervals to detect bone marrow toxicity during treatment with thiopurine drugs. The CBC is a common blood test that measures the number of red blood cells, white blood cells and platelets.

Does allopurinol inhibit TPMT?

Inhibition of TPMT by allopurinol would explain these results; however both in vitro and in vivo studies have shown a lack of inhibition of erythrocyte and human liver cytosolic TPMT activity following the addition of both allopurinol and its active metabolite, oxypurinol (alloxanthine) [29].

What is the TPMT gene?

The TPMT gene provides instructions for making an enzyme called thiopurine S-methyltransferase (TPMT). This enzyme carries out a specific chemical reaction called S-methylation of a group of molecules known as aromatic and heterocyclic sulphydryl compounds.

What is normal TPMT level?

Sies et al7 have established the normal range of TPMT to be 9.3–17.6 units/ml red blood cells. However, these results can have considerable inconsistencies as a result of factors such as recent blood transfusions, certain medications, alcohol, and interlaboratory variation.

What causes TPMT deficiency?

TPMT deficiency results from changes in the TPMT gene. This gene provides instructions for making the TPMT enzyme, which plays a critical role in breaking down (metabolizing) thiopurine drugs. Once inside the body, these drugs are converted to toxic compounds that kill immune system cells in the bone marrow.

What do low TPMT levels mean?

Complete TPMT deficiency (TPMT <10 nmol/h/g Hb) indicates that there is an absolute intolerance to thiopurine drugs. Low activity indicates partial enzyme deficiency and therefore that the probability of azathioprine-induced bone marrow depression or nausea is HIGH.

Is 50mg of azathioprine a lot?

The usual dose is 150-200 mg a day but the dose can vary depending on your weight and tolerance of the medication. Start with one 50 mg tablet daily usually in the morning with a meal. After one week, you should have your blood drawn.

What does allopurinol do to azathioprine?

Allopurinol interferes with the metabolism of azathioprine, increasing plasma levels of 6-mercaptopurine which may result in potentially fatal blood dyscrasias.

What causes low TPMT?

Where is the TPMT gene?

Thiopurine methyltransferase or thiopurine S-methyltransferase (TPMT) is an enzyme that in humans is encoded by the TPMT gene. A pseudogene for this locus is located on chromosome 18q.

Why is TPMT important?

Clinical importance of the TPMT polymorphism In hematopoietic tissues, TPMT catalyses the predominant inactivation pathway of thiopurines; hence, patients who inherit TPMT deficiency accumulate excessive concentrations of the active thioguanine nucleotides, with standard doses of these medications.

What is the best time of day to take azathioprine?

Azathioprine is best taken on an empty stomach, at least 1 hour before or 3 hours after food or milk. But if azathioprine makes you feel nauseous or sick, try taking it after food or at bedtime, or ask if you can divide your dose and take it twice a day. Swallow your tablets whole with a drink of water.

What is thiopurine S-methyltransferase ( TPMT ) deficiency?

Collapse Section Thiopurine S-methyltransferase (TPMT) deficiency is a condition characterized by significantly reduced activity of an enzyme that helps the body process drugs called thiopurines. These drugs, which include 6-thioguanine, 6-mercaptopurine, and azathioprine, inhibit (suppress) the body’s immune system.

Where is thiopurine methyltransferase gene located in humans?

From Wikipedia, the free encyclopedia Thiopurine methyltransferase or thiopurine S-methyltransferase (TPMT) is an enzyme that in humans is encoded by the TPMT gene. A pseudogene for this locus is located on chromosome 18q.

Where is the TPMT gene located in humans?

Thiopurine methyltransferase or thiopurine S-methyltransferase ( TPMT) is an enzyme that in humans is encoded by the TPMT gene. A pseudogene for this locus is located on chromosome 18q. Thiopurine methyltransferase methylates thiopurine compounds.

What is the role of TPMT in drug metabolism?

TPMT is best known for its role in the metabolism of the thiopurine drugs such as azathioprine, 6-mercaptopurine and 6-thioguanine. TPMT catalyzes the S-methylation of thiopurine drugs.