What is a DPYD (dihydropyrimidine dehydrogenase) test and why do I need it?

Who is the leaflet for? Who needs a DPYD test?

Everyone who is offered capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy will have a DPYD test before they start treatment.

What is DPYD?

DPYD is a gene that produces an enzyme called dihydropyrimidine dehydrogenase (known as DPD). The DPD enzyme helps the body to break down some types of chemotherapy. This includes the drugs capecitabine, 5-fluorouracil (5-FU) and tegafur.

The DPD enzyme stops the drug from building up in the body and causing side effects.

What is the DPYD test?

The DPYD test is a simple blood test. It is sometimes called a DPD test. The blood test checks for the gene changes that are most likely to cause low levels of the DPD enzyme.

Why are DPYD tests needed?

People with low DPD enzyme levels can have serious side effects from capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy treatments. These can be life-threatening.

We use this test to check your risk of low DPD enzyme levels before you start these types of chemotherapy.

Around 1 in 20 people have a low level of the DPD enzyme. This does not usually cause problems. But people with low levels are at more risk of serious side effects from capecitabine, 5-fluorouracil (5-FU) or tegafur chemotherapy. These side effects can include:

• severe diarrhoea
• feeling or being sick (vomiting)
• a sore or inflamed mouth or gut
• a reduced number of white blood cells in your blood, which can weaken your immune system and make you more likely to get infections

You can get more information about possible side effects of your chemotherapy from your chemotherapy information sheet or cancer team.

What happens if I have low DPD enzyme levels?

Most people will have normal DPD levels. But if you have low levels, your clinical team will talk to you about ways they can reduce your risk of serious or life-threatening side effects. This may include having:

• a lower dose of the chemotherapy to start with
• a different type of chemotherapy

If you have side effects

You may get side effects from chemotherapy even if your DPD levels are normal, and even if you started on a lower dose. If you have any side effects, it is still important to tell your cancer team.

If you have any side effects from your treatment, always contact your cancer team on the 24-hour contact number you have been given.