I am not a medical health professional and any comments I post are not intended, nor should they be construed, as medical advice. If you believe you are experiencing a medical emergency, dial 911 (where applicable) or contact proper emergency service personnel.
This is a somewhat common question in many DNA related groups. It depends on who you ask and what website you believe. It also depends on if you did a spit kit or cheek swab.
Let’s start out with one of the biggest differences between cheek swab tests, like FamilyTree DNA (FTDNA) and some other DNA companies use, and spit kit tests used by AncestryDNA, 23andMe, and a number of other DNA companies. Cheek swabs rely on the DNA in the skin cells of your cheek that is swabbed. Spit kits rely in large measure on the White Blood Cells (WBC) in your spit to obtain your DNA. Both chemo and radiation tend to temporarily deplete your WBC count
Here are two answers from Ancestry:
Not exactly the same responses.
Here’s three (3) responses from 23andMe:
https://customercare.23andme.com/hc/en-us/search?utf8=%E2%9C%93&query=chemotherapy&commit=Search. All of the responses give the same answer:
However, if you are undergoing medical treatment that reduces your white blood cell count, such as chemotherapy, it is best to wait at least two weeks after your last treatment or until your white blood cell count has returned to normal.
FamilyTree DNA (FTDNA) uses a cheek swab, but here’s their take on the question – https://www.familytreedna.com/learn/using-the-kit/ive-blood-transfusion-radiation-therapy-surgery-recently-will-affect-sample/:
I’ve had a blood transfusion, radiation therapy, or surgery recently. Will this affect the sample?
We recommend waiting one week after having serious surgery or radiation therapy before taking a sample. We suggest waiting 1-2 weeks after a blood transfusion as well. However, even if you take the sample right away, the medical treatment you have had should not affect the sample, and we will be able to get a good result.
Medical situations that would be of concern would be: known genetic disorders, bone marrow transplants, and/or facial reconstruction with donor skin grafts in the mouth. In any of these cases, please contact us and discuss the specifics of your situation to determine if we can get a usable sample.
Here’s LivingDNA‘s answer – they also use a cheek swab: https://support.livingdna.com/hc/en-us/articles/360012528151-Will-my-chemotherapy-treatment-affect-the-collection-
We often get asked if there is anything that can affect the sample collection rate or the results of the DNA testing. This is a much broader question than you might think and much more difficult to give a black and white response to.
Our bodies are fantastic things and it’s difficult to say exactly what the effects of specific drugs of treatment can have on it. We know that different people can have the same treatment and experience differing side effects and also the severity of those effects will vary.
With chemotherapy treatment, we do know that this has the ability to affect the DNA you have and it can damage the parts that we look at in order to provide you with results. In this case, we recommend that you allow 6 months from the date of your last treatment to take your DNA sample.
If you have any further concerns about past, present or future treatment and your results with us, please can we ask you to check with your healthcare provider, as they will have a far greater knowledge than ours and will therefore be able to give you advice that’s correct for you.