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Tuesday, September 30, 2008

TPMT Blood Test

The blood test for TPMT is also known as Thiopurine s-methyltransferase. It's a liver enzyme important to the metabolism of azathioprine (Imuran), and 6-mercaptopurine (6-MP).

Each person’s ability to metabolize thiopurines through the liver is different. I've read that it is only known to affect caucasians. The majority have no problem processing Imuran. However, a very small percentage have almost no ability to do so. One article says, "with 0.3–0.6% having very low (negligible) activity and approximately 10% having decreased activity compared with the remaining population.

Apparently, I fall into the 10% category, as my test results were
called Intermediate. I am so GLAD I was tested even though the chances were minimal.

The test is ordered when patients are about to start treatment or if the patient is having side effects due to TPMT deficiency. The test identifies those at risk of developing severe side effects such as lowering of blood cell counts.

If regular dosages are ordered, a major deficiency of TPMT can usually cause life-threatening bone marrow depression (myelosuppression) This happens because the drug builds up a toxicity in the body due to the lack of metabolization.

When a patient has no TPMT enzyme, then the prescription will have to be changed to something else.

When a patient has a low blood TPMT activity the risk of less serious side effects are more likely just hair loss, stomach pain, diarrhea and inflammation of the pancreas.

If a patient has normal blood TPMT activity then then they can take a standard dose of a thiopurine drug.

When at the lab, I didn't understand why the technician said it was a Prometheus test. But, take a look at this site and you can learn about it.

I am slowly reading through what I can about TPMT and it is scary to realize how close a call this Imuran could have caused. But, seems I am being looked after, as I am still here.

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