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DPD testing for patient receiving 5FU or Capecitabine

DPD testing for patients receiving 5FU or capecitabine


This leaflet provides information on dihydropyrimidine dehydrogenase (DPD) testing. If you are due to receive 5FU or capecitabine chemotherapy as part of your cancer treatment, it will be necessary to have genetic blood test prior to starting treatment.  This is to check whether your body is able to breakdown the chemotherapy drugs safely or not.  This leaflet will explain why the test is needed in more detail. 


What is DPD?

DPD is an enzyme made by the liver.  It helps break down certain chemotherapy drugs (such as 5FU and capecitabine) that are used to treat cancer. 

DPYD is a gene.  Genes are our cells’ instruction manuals and tell our body how to work normally.  The DPYD gene helps to control how much DPD enzyme is made.  Changes in the DPYD gene can mean your body does not make enough (or any) of the DPD enzyme.  This is called DPD deficiency. 



Why am I being offered a DPD test?

If your body does not make enough DPD, the chemotherapy drugs can build up in the body.  This can cause more severe side effects than usual and in some situations may be life-threatening.  The side effects include:

  • a drop in the level of blood cells which may increase the risk of having infections, breathlessness and bleeding
  • diarrhoea, which can be severe
  • a sore mouth
  • feeling or being sick, which can cause dehydration
  • a severe skin reaction, which leads to peeling or blistering of the skin. 


What does the DPD test involve?

Before you start treatment, your oncologist will arrange for you to have a genetic blood test.  The blood test is sent to a genetic laboratory to look for changes in the DPYD gene.  The result will be available in about five days and will be sent back to your oncologist. 

Please be aware that your blood sample will only be tested for changes in the DPYD gene so you will not find out about your risk of any other genetic conditions. 


What action is needed if I am found to have a DPD deficiency?

The team responsible for your treatment will discuss the results with you prior to starting any treatment. If your DPD gene is normal, you can have a standard dose of chemotherapy.  This is because your body can break down the chemotherapy drugs.

If a change in the DPD gene is found, you may need lower doses of chemotherapy to reduce the chance of getting serious side effects.  In some cases, it may be necessary to avoid using these drugs altogether.  In this situation, alternative treatment options will be discussed with you.

The team will monitor you closely during treatment.  If you do not develop any serious side effects after the first few cycles of treatment, they may consider whether it is safe to increase the dose of chemotherapy.  This will only be done following a discussion with you about the benefits and risks of increasing the dose. 


Will reducing the dose of the chemotherapy drugs affect how successful the cancer treatment is?

It is important that the risks of treatment are kept as low as possible, particularly as severe side effects may be life-threatening.  Your DPD level does not in itself affect how successful the chemotherapy will be in killing cancer cells, but it will tell us how your body will cope with the drug and the dose that is given. 


Is there anything I can do to increase the levels of DPD in my body?

There is no evidence that medications, dietary or lifestyle changes affect DPD levels.   The only action you need to take is to seek medical attention if you develop side effects following chemotherapy treatment.  In this situation you should inform the medical team that you are known to have a DPD deficiency. Contact Velindre Cancer Centre for advice.  The telephone number is at the end of the leaflet.


What does a diagnosis of DPD deficiency mean for my family?

DPD testing is only recommended for people being treated with 5FU or capecitabine chemotherapy.  There is no need to test your blood relatives who do not have a cancer diagnosis.  However other members of your family may also have a DPD deficiency.  This is because you share your genetics with blood relatives.  We would encourage you to share this information with your family in case they are treated for cancer in the future. 







Contact telephone numbers


Velindre Cancer Centre          029 2061 5888

Ask for the treatment helpline if you are unwell at home and need immediate advice at any time of the day or night. 


For more detailed information on DPD deficiency, please see below:

Cancer Research UK General Cancer Information on DPD deficiency


This information is also available in Welsh


This leaflet was written by health professionals.  The information contained in this leaflet is evidence based.

It has been approved by doctors, nurses and patients.  It is reviewed and updated every 2 years.


Originally prepared April 2020

Updated November 2022