Medical Oncologist
CION Cancer Clinics
Giving the sample for a genetic test | CION Cancer Clinics
Most genetic tests need only an ordinary blood sample from your arm. Some laboratories use saliva or a cheek swab instead, and all three carry the DNA you were born with. You do not need to fast. This page explains how each sample is taken, what to avoid before a saliva sample, and the few situations where a different sample is needed. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- How is the sample for a genetic test taken?
- Blood, saliva, cheek swab or skin: what is the difference?
- What happens when you give the sample?
- The sample words, in plain language
- Which sample suits which situation?
- Four things people assume about the sample
- What this page cannot tell you
- Common questions about giving the sample
The short answer
How is the sample for a genetic test taken?
Usually with an ordinary blood test from a vein in your arm. Some laboratories use saliva or a cheek swab instead. All three give the laboratory your DNA, which is the same in almost every cell of your body. You do not need to fast, and the sample takes a few minutes to give.
Why one small sample is enough
An inherited gene fault is present from birth in every cell. That means the laboratory does not need a sample from the organ where cancer grew. White cells in blood, or cells from the inside of your cheek, carry the same inherited instructions. The laboratory separates the DNA from those cells and reads the genes on your test.
What the sample is not
It is not a biopsy, and it does not involve surgery. It is also not the same as a tumour test, which looks for changes only inside the cancer and needs tissue from the tumour itself. That is a separate question, covered under targeted therapy.
The hard part of genetic testing is the conversation before it, not the sample.Four kinds of sample
Blood, saliva, cheek swab or skin: what is the difference?
The laboratory chooses the sample type. Your part is mostly to follow its instructions carefully.
Blood
The most common choice. A small tube is taken from a vein, exactly like a routine blood test. It gives plenty of good-quality DNA.
Good to know
- No fasting needed
- Can be taken near your home and sent on
- Bruising, if any, fades quickly
Saliva
You spit into a tube until it reaches a marked line. It suits people who dislike needles, and it can be done at home with a posted kit.
Do not eat, drink, smoke or chew paan or gutka for a while before. The kit states how long.Cheek swab
A soft brush is rubbed firmly inside your cheek, then sealed in a tube. It is quick and painless to give, though it collects less DNA than blood.
A small skin sample
Used in special cases. After a bone marrow or stem cell transplant, your blood and saliva can carry the donor's DNA. A tiny skin sample taken under local anaesthetic gives your own DNA instead.
Not sure whether this applies to you?
Ask an oncologistOn the day
What happens when you give the sample?
Consent comes first
The sample is taken only after pre-test counselling and after you have signed the consent form. If you have unanswered questions, ask them before the needle or the tube appears.
Your details are checked
Your name, date of birth and the test requested are checked against the form. Look at the label yourself. A misspelt name can delay a result.
The sample is taken
A blood draw takes a minute or two. Saliva takes a little longer, because it needs to reach the line. A cheek swab takes seconds.
It is packed and sent
The sample is sealed and sent to the laboratory, often by courier. Genetic laboratories are not in every town, so samples usually travel.
You go home
You can eat, drive and work as normal. The waiting begins, and your counsellor will tell you how the result will be given.
Words you may hear
The sample words, in plain language
- DNA
- The long chemical code inside your cells that carries every gene. The laboratory extracts it from the sample before testing.
- Germline
- Present in every cell from birth, and so inheritable. Any of these samples can show a germline fault.
- Buccal swab
- The medical name for a cheek swab. Buccal simply means the inside of the cheek.
- EDTA tube
- The tube with a purple cap often used for genetic blood samples. It stops the blood clotting on its journey.
- Sample kit
- A box from the laboratory with a tube, instructions, a form and a return envelope. Follow its steps in order.
- Repeat sample
- A second sample asked for when the first could not be tested. It is a nuisance, not a sign that something is wrong with you.
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Side by side
Which sample suits which situation?
Your situation
The usual sample
Most adults
Blood, or saliva if the laboratory prefers it
Strong fear of needles
Ask whether saliva or a cheek swab is accepted
Living far from a clinic
A posted saliva kit, or a local blood draw
Current blood cancer
Ask the team. Blood may not show your inherited DNA
After a donor stem cell transplant
Usually a small skin sample
Commonly believed
Four things people assume about the sample
"I have to fast before a genetic blood test."
No. Your DNA does not change with food. Eat normally unless another blood test is being taken at the same time that needs fasting.
"They need a piece of the tumour to test my genes."
Not for inherited testing. The fault you were born with is in your blood and saliva too. Tumour tissue answers a different question about the cancer itself.
"Saliva gives a less accurate result."
When collected properly, saliva gives reliable results for most inherited tests. The main risk is a sample too small or contaminated by food, which means a repeat.
"Chemotherapy will spoil my sample."
Chemotherapy does not change the genes you inherited. Low blood counts can occasionally make a blood sample harder to use, so tell the team what treatment you are having.
Being straight with you
What this page cannot tell you
It cannot tell you which sample your laboratory wants. That depends on the laboratory and the test ordered. Your counsellor or the kit instructions will say. Follow those, even where they differ from what you read here.
It cannot tell you when the result will arrive
Timing depends on the test, the laboratory and how far the sample has to travel. Ask your counsellor for a realistic estimate, and ask what happens if a repeat sample is needed.
Who this does not apply to
If you have a blood cancer, or have had a donor transplant, the usual advice does not fit you. Your inherited DNA may not be in your blood. Tell the team about your diagnosis before any sample is taken, so they can choose the right one. What your eventual result means is a question for the counsellor who ordered the test.
If a kit has arrived and you are unsure how to use it, call before you collect the sample, not after.Questions we are asked
Common questions about giving the sample
Does it hurt?
A blood draw feels like any other blood test: a sharp scratch and some pressure. Saliva and cheek swabs do not hurt at all. If you feel faint with needles, say so, and you can lie down while the sample is taken.
Can the sample be taken at home?
Often, yes. Saliva kits can be posted and returned by courier, and some laboratories arrange home blood collection. Ask your counsellor what your laboratory offers. Consent and counselling still come first, even if the sample is taken at home.
Can I eat before a saliva sample?
Not immediately before. Food, drink, tobacco, paan and chewing gum can spoil the sample. The kit states how long to wait. Rinsing your mouth with plain water is usually allowed, but follow the kit's own instructions.
I had a blood transfusion recently. Does it matter?
Tell the team before the sample is taken. In most cases it causes no problem for inherited testing. The laboratory may still ask for a different sample type, or for the sample to be taken later.
Can my sample be taken in my district and sent to Hyderabad?
Usually, yes. Many genetic samples travel by courier to a central laboratory anyway. Ask your counsellor whether a local collection centre can take it, and check the tube and form are the ones your laboratory needs.
What happens if the sample fails?
The laboratory will ask for a repeat. This happens occasionally, most often with saliva that was too little or collected too soon after eating. It is frustrating, but it says nothing about your genes.
What happens to my sample afterwards?
Laboratories often store leftover DNA for a period, and some ask to use it for research. Your consent form should explain this. You can say no to storage or research without affecting your test.
Can a child give a saliva or cheek sample?
Yes, when testing a child is appropriate. Cheek swabs are often easier for young children than blood. Most testing for adult-onset cancer risk waits until a child can decide for themselves, so ask your counsellor first.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
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Sources
- MedlinePlus Genetics — How is genetic testing done?
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What is the difference between germline and somatic mutations?
- NHS — Predictive genetic tests for cancer risk genes
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Which sample type is more reliable?Blood against saliva, compared honestlyCan a genetic test be done from a tissue block?When stored tissue is the only optionHow long until you get the result?What happens after the sample leavesInformed consent for genetic testingWhat you agree to before the sample is taken
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Unsure which sample your test needs?
Tell us which test has been suggested and we will explain how the sample is collected and where. One helpline serves every CION centre.