Medical Oncologist
CION Cancer Clinics
What happens if the genetic test sample fails | CION Cancer Clinics
If a sample fails, the lab tells the doctor who ordered the test and asks for a new one. A failed sample says nothing about your genes. It means only that the lab could not get a reliable reading from that tube. This page explains the usual causes, what happens next, who usually pays for the repeat, and how to stop it happening a second time. 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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The short answer
What happens if my genetic test sample fails?
The lab tells the doctor who ordered the test, and a new sample is usually requested. A failed sample says nothing about your genes. It means only that the lab could not get a reliable reading from that particular tube, and the result will be delayed while a fresh one is collected.
How often it happens
It is uncommon with a fresh blood sample that reaches the lab in good time. It is more common with saliva kits that were not filled properly, with samples delayed in transit, and with old tissue blocks from a relative who has died. Knowing the common causes makes most failures avoidable.
Why a lab would rather reject than guess
An inherited result can shape decisions for the whole family. A lab that reports from a poor sample risks missing a fault or reporting one that is not there. Stopping and asking for a new sample is the careful choice, even though it is frustrating for you.
A failed sample is a delay, not a result. It does not mean anything was found.The usual causes
Why do genetic test samples fail?
Most failures come from one of four problems, and most of them happen before the sample reaches the lab.
Too little DNA
A saliva tube not filled to the line, or a cheek swab with too few cells, may not give the lab enough to work with.
DNA damaged on the way
Heat, long delays and leaking tubes all break DNA into pieces too small to read reliably.
Common in
- Samples left in a hot vehicle
- Couriers held up over a holiday
- Tubes packed without their sealed bag
Labelling problems
If the name on the tube does not match the form, the lab cannot be sure whose DNA it is. It will not test a sample it cannot trust.
Old or treated tissue
Tissue blocks stored for years, especially from a relative who has died, often hold damaged DNA. Some can still be tested. Some cannot, and there may be no second block to try.
Not sure whether this applies to you?
Ask an oncologistAfter a failure
What happens next, step by step?
The lab informs your doctor
The ordering clinician or counsellor hears first, usually with the reason the sample could not be used.
You are told and asked for a new sample
Someone from the hospital or lab calls to explain and arrange a new collection. Ask what went wrong so it is not repeated.
The repeat is arranged
A fresh blood sample is often the safest choice after a saliva failure. A new consent form may not be needed, but the labels are checked again.
The clock restarts
The waiting time usually runs from when the new sample arrives. If treatment decisions depend on the result, tell the lab so it can prioritise.
Ask who pays for the repeat
Many labs repeat free when the problem was on their side or in transit. Some charge when the sample was mishandled before collection. Ask before the new sample is taken.
On the lab's message
The words you may hear, in plain language
- Quality control failure
- The lab's own checks found the sample or the reading was not good enough to report from.
- Insufficient DNA
- Too little genetic material was recovered from the sample to run the test properly.
- Degraded sample
- The DNA was broken into small pieces, usually by heat, time or the way tissue was preserved.
- Sample mismatch
- The details on the tube and the form did not agree, so the lab could not confirm whose sample it was.
- Low coverage region
- A part of a gene the lab could not read well even though the rest of the test worked. The report should list it.
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Side by side
How to stop it happening twice
What went wrong
What helps next time
Saliva tube not filled to the line
Take your time, or ask for a blood draw instead
Sample held up in a courier
Collect early in the week, avoiding holidays
Name spelt differently on tube and form
Check both against one identity document
Old tissue block too damaged
Ask whether a living relative can be tested instead
Commonly believed
Four things families fear when a sample fails
"They are asking for another sample because they found something."
No. A repeat request means the first sample could not be read reliably. Labs do not ask for a new sample to confirm a finding without telling your doctor that is the reason.
"My DNA must be unusual if it would not work."
Failures are about the tube, not the person. Your genes do not make a sample harder to read. A fresh, well-handled sample almost always works.
"We will have to pay the full price again."
Often you will not. Many labs repeat free when the problem was not your fault. Ask what the lab's policy says before the new sample is taken.
"If Amma's tissue block fails, nobody can be tested."
Living relatives can often be tested instead, starting with those most closely related to her. A counsellor can plan the order so the family still gets an answer.
Being straight with you
What this page cannot tell you
It cannot tell you why your particular sample failed. Only the lab knows that, and it will explain the reason to the doctor who ordered the test. Ask them to pass it on in plain words.
It cannot tell you whether a partial result is enough
Sometimes most of the test works and a small part of a gene cannot be read. Whether that gap matters depends on your family history and the genes involved. What your specific report means is a question for the counsellor who ordered the test.
Who this does not apply to
Most people who give a fresh blood sample will never face a failure. This page is about inherited tests. A tumour test that fails because the biopsy was too small is a different problem, covered under targeted therapy.
If you have been told a sample failed and nobody has explained why, call and ask. You are entitled to know.Questions we are asked
Common questions about failed samples
Does a failed sample mean the test found a problem?
No. It means the lab could not get a reliable reading from that tube. It says nothing about whether you carry a fault. A new sample is needed before anyone can answer that question.
How much longer will the result take?
The waiting time usually restarts when the new sample arrives at the lab. If a surgery or treatment decision depends on the result, tell your doctor, who can ask the lab to prioritise the repeat.
Should I switch from saliva to blood after a failure?
Often that is the safest choice, because blood gives more DNA. If there is a reason to avoid a needle, a carefully collected saliva sample can still work. Ask the lab which it prefers.
Can a tissue block be tested again if the first attempt failed?
Sometimes, if another block from the same surgery exists. The hospital that did the surgery may still hold it. If not, the counsellor may suggest testing a close living relative instead.
Who pays for the repeat test?
It depends on the lab and on the reason. Many labs repeat free when the problem arose in the lab or in transit. Some charge when the sample was not collected as instructed. Ask for the policy in writing.
What does it mean if only part of the test failed?
The report should list any areas the lab could not read. Some gaps matter and some do not, depending on your family history. Your counsellor will say whether extra testing is needed to fill them.
Can a sample fail because of medicines or chemotherapy?
Ordinary medicines do not affect an inherited DNA test. A recent bone marrow transplant, or some blood cancers, can make blood and saliva unsuitable. Tell the counsellor about these before any sample is taken.
Who can help if the lab is not responding?
Start with the doctor or counsellor who ordered the test. If you tested through CION, call the helpline with your sample number, and someone will chase the lab and tell you where things stand.
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
Medical Oncologist
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Sources
- MedlinePlus Genetics — How is genetic testing done?
- MedlinePlus Genetics — What is the cost of genetic testing, and how long does it take to get the results?
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- Cancer Research UK — Genetic testing 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.
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Told your sample failed and not sure why?
Share your sample number and what you were told. We will find out what went wrong and help arrange the repeat. One helpline serves every CION centre.