Medical Oncologist
CION Cancer Clinics
Carrier, diagnostic and predictive testing: three questions, not three machines | CION Cancer Clinics
Carrier, diagnostic and predictive testing often use the same laboratory method. What changes is who is being tested and why: someone who already has cancer, a well relative checking for a known family fault, or someone checking what they could pass to a child. This page sets out the difference plainly and explains which usually comes first. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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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
- Carrier, diagnostic and predictive testing: what is actually different?
- How do the three purposes actually differ?
- What does each type of test actually mean for the person having it?
- The words this report uses, in plain language
- What order does testing usually happen in?
- What this page cannot tell you
- Four things families assume about these three tests
- Common questions about carrier, diagnostic and predictive testing
The short answer
Carrier, diagnostic and predictive testing: what is actually different?
These three names do not describe three different laboratory methods. They describe three different questions being asked of the same kind of test. The sample can be identical; what changes is who is being tested, why, and what the answer will be used for.
Why the name matters more than the method
A laboratory can run the same panel on two people and call the result something different, because one person already has cancer and is being tested to explain it, while the other is a well relative being tested to check whether they carry the same known family fault. The test does not change. The question behind it does.
Why families mix these up
Most people hear "genetic test" as one thing. In practice, whether you are the first person tested in a family, a well relative checking for a known fault, or someone checking whether you could pass something to a child, changes what the result can and cannot tell you.
Ask which of the three your test is before it is done. It changes what a negative result means afterwards.Side by side
How do the three purposes actually differ?
Who is usually tested
What the result is used for
Diagnostic: someone who already has cancer
Explains whether an inherited fault is behind the cancer they already have
Predictive: a well relative of someone with a known fault
Tells them whether they carry that exact fault before any cancer appears
Carrier: someone planning a family, or asked about a recessive condition
Tells them whether they could pass a fault to a child, without raising their own risk
Common thread
The laboratory method can be identical across all three
Each one, in plain terms
What does each type of test actually mean for the person having it?
The words sound technical. What each one means for you is simple once it is set out plainly.
Diagnostic testing
Done on someone who already has cancer, to find out whether an inherited fault is behind it. A positive result here is what makes testing relatives worthwhile, because it gives them an exact fault to test for.
Predictive testing
Done on a well relative once a fault has already been found in someone else in the family. It answers one question only: do you carry that exact fault.
Usually offered alongside
- Counselling before the test, not only afterwards
- A clear explanation of what a positive result would mean for screening
- No pressure to test before you feel ready
Carrier testing
Usually about conditions that need a fault from both parents to cause illness in a child. Carrying one copy does not raise your own cancer risk in most of these conditions, but it can matter for family planning.
Why the label changes the conversation
The counselling before a diagnostic test is about explaining a cancer that already happened. The counselling before a predictive test is about a well person deciding whether they want to know. These are different conversations, not the same one repeated.
Not sure whether this applies to you?
Ask an oncologistOn your report
The words this report uses, in plain language
- Proband
- The first person in a family to be tested, usually someone who already has cancer.
- Cascade testing
- Testing relatives, one by one, once the proband's exact fault is known.
- Autosomal recessive
- A pattern where a condition only appears in a child who inherits a faulty copy from both parents.
- Pre-test counselling
- A conversation before testing about what each possible result would mean, so the decision to test is an informed one.
- Uninformative result
- A negative predictive test in a family where the proband's own fault was never actually found, so the negative cannot be fully trusted.
How a family usually moves through this
What order does testing usually happen in?
The person with cancer is tested first
Diagnostic testing on the proband is the usual starting point, because it tells the family whether there is a specific fault to look for at all.
A fault is found, or it is not
If nothing is found, predictive testing of well relatives usually adds little. If a fault is found, the family now has an exact target.
Relatives are offered predictive testing
Each relative decides, in their own time, whether they want to know if they carry that exact fault.
Carrier testing is a separate conversation
It is usually raised only when family planning, or a specific recessive condition, is the actual question being asked.
Being straight with you
What this page cannot tell you
It cannot tell you which of the three tests fits your situation. That depends on whether anyone in your family has already tested positive, whether you already have cancer yourself, and what question you are actually trying to answer. A genetic counsellor works this out with you directly.
It cannot make the decision to test for you
Predictive testing in particular is a choice, not an obligation. Some relatives want to know as soon as possible; others prefer to wait, or never test at all. Both are reasonable, and a counsellor will support either choice.
Who this does not apply to
If nobody in your family has a known gene fault, predictive testing is not yet available to you, because there is no specific target to test for. Diagnostic testing of the person already affected usually needs to happen first.
If you are unsure which of these three describes your situation, call the helpline and describe who in your family has been tested so far.Commonly believed
Four things families assume about these three tests
"They are three different technologies, so one
must be more advanced than the others."
The laboratory method is often identical. The difference is entirely in who is being tested and why, not in which machine or method is used.
"If my relative's diagnostic test is negative, my
predictive test is not needed."
A negative diagnostic test in the person with cancer usually means no specific fault was found to test relatives for at all, which is a different situation from a relative testing negative for a known fault.
"Carrier testing means I am at higher risk of
cancer myself."
For most conditions checked by carrier testing, carrying one copy does not raise your own risk. The concern is mainly about what could be passed to a child.
"Predictive testing is only worth doing if I am
certain I want to know."
Counselling before the test exists precisely because certainty is not required beforehand. Many people are unsure until they have talked it through, and that is exactly what the conversation is for.
Questions we are asked
Common questions about carrier, diagnostic and predictive testing
Which test should the first person in my family
have?
Usually diagnostic testing, done on whoever already has cancer. It tells the family whether there is a specific fault to look for, which is needed before anyone else is offered predictive testing.
What does an uninformative negative mean?
It means the person who already had cancer tested negative, but no specific fault was ever confirmed in the family to test other relatives for. It is different from a relative testing negative for a known, confirmed fault.
Can I have predictive testing if nobody in my family has
been tested yet?
Usually not straightaway. Predictive testing checks for one exact, already-known fault. Without that starting point, the person with cancer usually needs diagnostic testing first.
Does carrier testing affect my own cancer risk?
For most conditions covered by carrier testing, no. Carrying one copy of a recessive fault does not usually raise your own risk; the relevance is mainly for children if your partner carries the same fault.
Am I obliged to have predictive testing if my relative
tested positive?
No. Predictive testing is entirely your choice. Some people want to know as soon as possible; others wait, or decide not to test at all, and both are respected.
Is diagnostic genetic testing the same as a biopsy?
No. A biopsy examines tumour tissue. Diagnostic genetic testing, in this sense, checks blood or saliva for an inherited fault that may explain why the cancer happened.
What happens if my predictive test is positive?
A genetic counsellor explains what it means for your screening and, if relevant, for your own family planning. A positive result raises risk; it does not mean cancer is certain.
Where do I start if I am not sure which type of test my
family needs?
Speak to a genetic counsellor and describe who in your family has already been diagnosed or tested. Call the CION helpline if you are not sure who to approach 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
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What are the types of genetic tests?
- Cancer Research UK — Predictive genetic testing for cancer risk genes
- 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
Cancer genetics explainedThe starting logic behind testing the affected relative firstWhich test would your situation need?A wider guide to matching test type to situationA negative result: what it does and does not rule outWhy an uninformative negative differs from a true negativeHow to read a germline genetic test reportMaking sense of the report once testing is done
Talk to us
Not sure which of these three fits your family?
Tell us who has been diagnosed or tested so far and we will help you work out the right next step. One helpline serves every CION centre.