What Is — DPD Deficiency?
DPD is an enzyme in your body that breaks down certain chemotherapy medicines after they enter your bloodstream. If your DPD level is lower than normal, those medicines are not broken down at the usual speed and can build up to harmful levels. A blood test before treatment can show whether this applies to you.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- An inherited difference — DPD activity is shaped by a gene called DPYD that you are born with. A change in this gene can reduce how well the enzyme works.
- The drug builds up instead of clearing — Without enough DPD, fluoropyrimidine chemotherapy drugs stay in the body longer than expected, reaching levels that cause serious harm.
- It cannot be seen without testing — People with DPD deficiency look and feel completely normal before treatment. A blood test is the only way to know.
- Testing is done before treatment starts — DPD status can be checked from a blood sample before chemotherapy begins. Availability varies by centre in India.
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DPD is an enzyme your body uses to break down certain chemotherapy drugs, particularly 5-fluorouracil and capecitabine. If you have low or absent DPD activity, these drugs accumulate in your body rather than clearing normally. A blood test can identify this before treatment begins.
What is the DPD enzyme and what does it do?
DPD — dihydropyrimidine dehydrogenase — is an enzyme made mainly in the liver. Its job is to break down a family of chemotherapy drugs called fluoropyrimidines. This family includes 5-fluorouracil (5-FU) and capecitabine, two of the most commonly used chemotherapy medicines in cancer care across India and worldwide.
After one of these drugs enters your body, DPD begins breaking it down so that it can be cleared safely. This happens continuously in the background. Most of the drug is processed this way before it reaches a harmful level.
The instructions for making DPD are carried in a gene called DPYD. Changes in DPYD — present from birth and not caused by anything you did — can reduce how much DPD the body produces, or make the enzyme work less efficiently. Testing looks for these changes.
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What happens when DPD activity is too low?
When DPD activity is reduced, the drug breaks down more slowly than your oncology team's standard planning assumes. The drug stays in your body longer and reaches higher concentrations. At a dose that is safe for someone with normal DPD activity, this can cause severe toxicity.
Complete DPD deficiency is uncommon. Partial deficiency — where the enzyme works, but less effectively than normal — is more common and is often not identified before treatment. ESMO and EMA guidance, developed largely from European population data, notes that partial deficiency is more prevalent than most people would expect. Research into variant frequencies in Indian populations is more limited and continues to develop.
In a person with undetected deficiency receiving a standard dose, the toxicity that results can be severe — affecting the gut lining, the blood count, and the nervous system — and can progress quickly. This is not the ordinary side-effect profile of chemotherapy; it tends to be more severe and can appear earlier. It cannot be predicted by looking at a person or by their previous health history.
Testing is done from a blood sample. It looks either at the DPYD gene directly or at actual DPD enzyme activity in the blood. Where testing is available and ordered by your oncologist before treatment begins, the result gives your team information they can factor into planning. Ask your oncologist whether DPD testing is available at your centre before starting a fluoropyrimidine-based regimen.
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Frequently asked questions
Which chemotherapy drugs are affected by DPD deficiency?
5-fluorouracil (5-FU) and capecitabine are the main ones, along with tegafur-based regimens. These all belong to a drug family called fluoropyrimidines, and they all rely on DPD to be cleared from the body. If your oncologist mentions any of these drugs by name, DPD is the relevant enzyme to ask about. Your oncologist will tell you which drug applies to your specific regimen.
What kind of toxicity can DPD deficiency cause?
In a person with undetected DPD deficiency, standard-dose fluoropyrimidine treatment can cause severe damage to the gut lining, a deep fall in white blood cells, and effects on the nervous system. This can appear after the first or second treatment cycle and progress quickly. It does not look like typical chemotherapy side effects — it tends to be more severe and earlier in onset. The degree of risk depends on how much enzyme activity is reduced.
How is DPD tested?
There are two approaches. One looks at the DPYD gene in a blood sample to identify known variants associated with reduced enzyme activity. The other measures DPD enzyme activity in the blood directly. Both require a blood sample. Neither test is universally available across all centres in India. Ask your oncologist which type is accessible to you and whether it can be arranged before your first treatment.
Is DPD testing required in India before chemotherapy?
Not as a universal requirement. In parts of Europe, the EMA required DPD testing before fluoropyrimidine treatment from 2020. In India, CDSCO had not mandated it as of the date this page was written, and availability depends on where you are being treated. Asking your oncologist directly is the most reliable way to find out what is available in your case. The question is always worth asking.
If I have a DPD variant, does that mean I cannot have the chemotherapy?
Not automatically. The presence of a DPYD variant does not by itself determine whether you can or cannot receive the drug. Your oncologist interprets the result alongside your cancer type, the treatment being considered, and your overall health. Testing gives your treating team information they can factor into their planning. What that means for your specific result and situation is a conversation for your oncologist, not something a web page can answer.
Should all patients having fluoropyrimidine chemotherapy be tested?
ESMO and CPIC have both published guidance supporting DPD testing before fluoropyrimidine chemotherapy. Whether testing is offered in your case, and what is available at your centre, depends on your treating team and their resources. The guidance supports offering the test, but your oncologist makes the decision for your specific circumstances. Asking about it at your next appointment is a reasonable step.
Does DPD deficiency run in families?
DPD activity is determined largely by the DPYD gene, which is inherited. If you carry a significant DPYD variant, your biological relatives have a higher chance of carrying the same variant than the general population. Whether those relatives need testing — and in what circumstances — is a question for a clinical genetics service rather than a self-referral. Your oncologist can advise whether a genetics referral is appropriate for your family.
How do I bring up DPD testing with my doctor?
Ask directly before treatment starts: 'Is my chemotherapy a fluoropyrimidine, and if so, has DPD testing been considered?' That question is specific and entirely appropriate to raise. If DPD testing is not available at your centre, that does not mean your care is inadequate — practice varies across India and the evidence continues to develop. But the question is worth asking, and a clear explanation of what is and is not available to you is reasonable to expect.
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