DPD Deficiency for 5-FU Response

Is Testing Right for Me? I Have My Test Results

DPD Deficiency for 5-FU Response

  • Author: Nicole Teed, MS, CGC
  • Reviewer: Julie Pippens, PharmD
  • Last updated: 2011-11-15

Pros and Cons

Everyone who is deciding whether or not to get genetic testing should first ask:

  • "Why am I getting tested?"
  • "What will this test mean for me?"
  • "What are the benefits of testing?"
  • "Are there any implications I should consider?"

In general, the advantages for drug response tests outweigh the potential negative effects. Some of the concerns that are common for other types of genetic tests – like discrimination issues or the impact on family members – don't apply as much to this type of test. However, genetic testing is always a choice. If you are considering a genetic test for drug response, you may want to consider some of the issues listed below.

Pros Cons
  • Testing for gene variants will find most of the variants that cause abnormal drug response.
  • If testing finds a variant, the results are very reliable.
  • These test results may help your doctor tailor your drug therapy to you by choosing drugs or doses that are safest and most effective.
  • These test results may help you avoid drug side effects, some of which can be quite serious.
  • Even if you have normal test results, you could still experience a poor drug response. No test can predict your response completely, because other factors can affect drug response including your health, lifestyle, and other genes.
  • Insurance doesn't always cover genetic testing and testing can be quite expensive.
  • You may be disappointed if results show you shouldn't use a drug because the risk of side effects or poor response is too high.

Next: Genetics of Drug Response

Why are you considering DPD deficiency testing for 5-FU response?

I am considering starting 5-FU to treat a medical condition.

I am currently taking/using 5-FU and I'm not having any problems with it.

I am currently taking/using 5-FU and I'm having side effects.

None of these

DPD deficiency testing for 5-FU response may be useful for you. Some people have an increased sensitivity to 5-FU and are at risk for severe side effects. People with a known DPD deficiency (not enough DPD enzyme) should not take 5-FU. People who develop symptoms of DPD deficiency while taking 5-FU should stop taking it. However, the FDA does not require or recommend testing for DPD deficiency before this drug is prescribed. At this point, the testing decision is left up to the doctor and the patient.

You should talk to your doctor to learn if DPD deficiency testing would make a difference for your healthcare. The table below sums up how test results may change your care.

Test Result Chance To Get This Result
What This Result Means
Normal DPD ~92%
  • You metabolize the drug normally.
  • You have a lower chance for side effects.
  • You can take the usual dose of the drug.
Intermediate DPD ~7%
  • You metabolize the drug more slowly.
  • You may have a higher chance for side effects.
  • Most people with this result can still take 5-FU, but should start with half the usual dose.
Low or absent DPD~1%
  • You cannot effectively metabolize this drug.
  • You have a high risk of toxic side effects.
  • You should not take this drug. Your doctor may consider a different treatment for you.

DPD deficiency testing for 5-FU response may not be useful for you. Some people have an increased sensitivity to 5-FU and are at risk for severe side effects. People with a known DPD deficiency (not enough DPD enzyme) should not take 5-FU. People who develop symptoms of DPD deficiency while taking 5-FU should stop taking it. However, the FDA does not require or recommend testing for DPD deficiency when this drug is prescribed. At this point, the testing decision is left up to the doctor and the patient.

Most people who have DPD deficiency will show signs of 5-FU toxicity after the first treatment. Since you are taking/using the drug without any side effects, testing at this point is probably not that helpful for you. You should continue to be monitored for side effects like everyone else who takes/uses 5-FU. Be sure to mention any concerns or issues you might be having with your doctor immediately.

DPD deficiency testing for 5-FU response may be useful for you. Some people have an increased sensitivity to 5-FU and are at risk for severe side effects. People with a known DPD deficiency (not enough DPD enzyme) should not take 5-FU. People who develop symptoms of DPD deficiency while taking 5-FU should stop taking it. However, the FDA does not require or recommend testing for DPD deficiency when this drug is prescribed. Some doctors may decide that testing is useful to find out if DPD deficiency explains your side effects.

  • If testing finds two gene variants and/or low-to-absent levels of DPD, you have high risk for drug toxicity. You should not take 5-FU. These results likely explain your side effects. Your doctor may want to try a different treatment.
  • If testing finds a gene variant and/or intermediate levels of DPD, you may have a higher risk for drug toxicity, but you may be able to tolerate a lowered dose. Your doctor may try lowering your dose, or your doctor may talk to you about changing to a different treatment.
  • If your test results are normal, DPD deficiency is not likely the cause of your side effects. Other factors may be affecting the way you break down this drug. Your doctor will have to make a decision about whether to lower your dose or change to a different drug therapy by weighing the benefits you are getting against the side effects.

DPD deficiency testing for 5-FU response may not be useful for you. Testing is not recommended for people who aren't starting or currently taking 5-FU. See Who Should Consider Testing for the main reasons for testing.

If you have a reason for testing that isn't covered here, talk to your doctor or a genetic counselor about whether testing might be useful for you.