Medical Oncologist
CION Cancer Clinics
Testing parents, siblings and children | CION Cancer Clinics
Parents, full siblings and children are first-degree relatives, each sharing roughly half their genes with the person tested. Once a fault is confirmed, this is usually the first group offered a targeted test. Here is exactly who counts, how they are approached, and what changes their result. At CION Cancer Clinics, our team helps carriers and their families plan checks, next steps and support after a genetic result.
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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
- Who counts as a first-degree relative in genetic testing?
- The people counted as first-degree relatives
- How first-degree relatives are actually approached
- Words used to describe close relatives
- First-degree relatives and second-degree relatives
- What this page cannot tell you
- Four things people assume about first-degree testing
- Common questions about first-degree relatives
The short answer
Who counts as a first-degree relative in genetic testing?
Parents, brothers and sisters, and children. Each of these relatives shares roughly half their genes with the person tested, which is why they are usually the first group offered testing once a fault is confirmed in the family.
Why this group comes first
Once a fault is found, each first-degree relative has an even chance of carrying the same one, independent of the others. That is a high enough chance, and a close enough relationship, that testing is normally offered to the whole group at once rather than one at a time.
What makes this group different from the rest
Second-degree relatives, such as grandparents or aunts and uncles, share a smaller proportion of genes and are usually only approached once the picture within the first-degree group is clearer. Starting close and working outward keeps the process manageable.
Why the result is usually clearer for them
The relative who tested first had a broad panel that searched many genes. A first-degree relative has a targeted test for the one fault already known. It is simpler, it usually costs less, and the answer is normally a clear yes or no. Most families find that far easier to act on.
"First-degree" is a precise medical term. It is not the same as "closest relative" in the everyday sense a family might use.Exactly who this means
The people counted as first-degree relatives
Four groups, defined by direct genetic relationship rather than by how close a family feels.
Parents
Mother and father. A fault could have come from either side, so both are usually considered, not just the side that seems to explain the family history. A father can carry a fault linked to breast or ovarian cancer without ever being ill himself.
Worth knowing
- A living parent's result can show which side the fault came from
- That tells you which aunts and uncles to approach next
Full siblings
Brothers and sisters who share both parents. Each one inherits independently, so one sibling's result does not predict another's. In many Telugu families a cousin is called brother or sister. For testing, only siblings who share both your parents count here.
Children
Sons and daughters. For adult-onset faults, testing usually waits until they are adults and can decide for themselves. A small number of syndromes are different, because screening starts in childhood and genuinely helps.
Who is not included
Half-siblings, grandparents and step-relatives are not first-degree by this definition, even where a family feels equally close to them. Adopted children are not included either, because testing follows birth relationships. They are still offered testing when their own birth family carries a fault.
Not sure whether this applies to you?
Ask an oncologistIn practice
How first-degree relatives are actually approached
The confirmed result is shared
The person tested, or a written family letter, explains the exact fault found and why it matters to this specific group.
Each relative sees a counsellor of their own
Testing a well relative is their own decision. They get their own appointment rather than being folded into someone else's.
A targeted test looks for the one fault
Because the exact change is already known, the test is simpler and the result is usually a clear yes or no.
Screening or reassurance follows
A positive result opens a screening plan and the next generation. A negative one usually returns that relative to ordinary care.
Terms in this group
Words used to describe close relatives
- First-degree relative
- A parent, full sibling or child. Each shares roughly half their genes with the person tested.
- Second-degree relative
- A grandparent, grandchild, aunt, uncle, niece, nephew or half sibling, sharing roughly a quarter of the same genes.
- Independent inheritance
- The fact that each sibling inherits separately from their parents. One sibling's result gives no certainty about another's.
- Adult-onset condition
- A cancer risk that typically only becomes relevant in adult life, which is why testing children for it is usually delayed.
- Pre-test counselling
- A conversation before testing, explaining what a result could mean, so the decision to test is genuinely informed.
- Consent
- Each adult relative's own agreement to be tested. Nobody, including a parent or sibling, can consent on another adult's behalf.
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Side by side
First-degree relatives and second-degree relatives
First-degree
Second-degree
Parents, siblings and children
Grandparents, aunts, uncles, nieces, nephews
Share about half the same genes
Share about a quarter of the same genes
Usually offered testing first
Usually reached through a positive first-degree result
An even starting chance of the fault
A lower starting chance of the fault
Being straight with you
What this page cannot tell you
It cannot tell you which of your specific first-degree relatives should test, or in what order among themselves. A counsellor works that out from your actual family tree and the exact fault involved. What your relative's specific variant means is a question for the counsellor who ordered the test.
It cannot make a reluctant relative agree
Being first-degree does not create an obligation to test. Some relatives choose not to, and that choice has to be respected, even where it leaves a gap in the picture. Some worry about marriage prospects, and India has no law that protects genetic results in insurance. Those worries are fair, and they belong in that relative's own counselling appointment.
It cannot plan for relatives who live far away
A brother in a district town or a sister abroad can usually be tested where they live. The family letter and a copy of the original report travel with them, so their laboratory knows exactly which fault to look for.
Who this does not apply to
If no fault has been confirmed anywhere in the family yet, there is no known target for first-degree relatives to be tested against. The starting point in that situation is testing the relative already affected, not the wider first-degree group.
If you are unsure whether you count as first-degree to the relative who tested, call the helpline and describe the relationship. Someone will tell you plainly.Commonly believed
Four things people assume about first-degree testing
"If my sibling is clear, I probably am too."
Each sibling inherits independently from their parents. One sibling's negative result gives no useful information about another's chances.
"Half-siblings count the same as full siblings for this."
Half-siblings share only one parent and are not counted as first-degree relatives, which changes both their starting risk and how testing is offered to them.
"Being first-degree means testing is compulsory."
It means testing is offered and usually recommended, never that it is required. Every adult relative decides for themselves.
"Children should be tested as soon as a parent's result is known."
For most adult-onset faults, testing waits until the child is an adult and can choose for themselves, whatever the parent's own result was.
Questions we are asked
Common questions about first-degree relatives
Does "first-degree" include grandparents?
No. Grandparents are second-degree relatives. First-degree is limited to parents, full siblings and children.
Are half-siblings first-degree relatives?
No, half-siblings share only one parent and are usually treated as a separate category, with their own starting chance of carrying a family fault.
Do all first-degree relatives need testing at once?
They are usually all offered testing once a fault is confirmed, but each decides on their own timeline. There is no requirement to test together.
What if a parent has already died?
Testing can still be offered to their children and other surviving first-degree relatives. A parent's own status can sometimes be inferred from the pattern seen in their children.
Can a first-degree relative refuse testing?
Yes, entirely. Being first-degree means testing is offered and recommended, not that it can be required of them.
Do adopted children count as first-degree relatives?
Genetically, no, since they do not share the family's genes by birth. Testing is based on biological relationship, not on the family unit itself.
How is my starting risk worked out as a first-degree relative?
Each first-degree relative starts with roughly an even chance of carrying a fault already confirmed in the family, before their own test result is known.
Where do I start if I am a first-degree relative of someone tested?
Call the helpline with a copy of their report or family letter. Someone will arrange a counselling appointment for your own testing decision.
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
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What is genetic testing?
- GeneReviews (NCBI) — Genetic Counseling
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
Cascade testing: how a result moves through a familyHow this group fits into the wider processHow far out in the family should testing go?What happens once this group is testedTesting a relative who has never had cancerWhat a well relative's own testing appointment looks likeObligate carriers: when testing is not neededWhen a first-degree relative's status is already certain
Talk to us
Is a parent, sibling or child of yours holding a result?
Bring us their report or family letter and we will arrange a counselling appointment for your own decision. One helpline serves every CION centre.