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Why two labs can classify the same variant differently | CION Cancer Clinics
Two laboratories can look at the same change in the same gene and reach different conclusions. It happens because classifying a variant is a judgement built from evidence, and laboratories see different evidence at different times. This page explains why disagreements happen, which ones actually change care, and what to do if your family has been given two different answers. 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
- Why would two labs classify the same variant differently?
- Four reasons two reports can disagree
- What should you do if two reports say different things?
- The words you will meet, in plain language
- Which disagreements matter, and which rarely do
- What this page cannot tell you
- Four things families believe when labs disagree
- Common questions about labs that disagree
The short answer
Why would two labs classify the same variant differently?
Because classifying a variant is a judgement, not a measurement. Each laboratory weighs the same kinds of evidence using shared international rules. They do not always hold the same evidence, and they do not always weigh it the same way. The result can be two honest answers that do not match.
The rules are shared, the evidence is not
Most laboratories follow a common framework published by the American College of Medical Genetics and Genomics, with five labels running from benign to pathogenic, meaning disease-causing. The framework says which kinds of evidence count. It cannot give every laboratory the same patient records, the same family studies or the same unpublished data.
Most disagreements are small
When laboratories disagree, it is usually by one step, such as likely pathogenic against pathogenic. Those differences rarely change care. The disagreements that matter cross the line between uncertain and harmful, because only a harmful label changes screening, surgery decisions and the testing of relatives.
A disagreement between laboratories is not proof that either one made a mistake.Where the difference comes from
Four reasons two reports can disagree
When families compare reports, the gap usually traces back to one of these.
Different evidence
One laboratory may have tested many families with the same variant and seen it travel with cancer. Another may never have seen it before. Private case data like this is often unpublished, so the second laboratory cannot use it.
Different dates
Evidence grows every year. A report issued several years ago reflects what was known then. A newer report on the same variant may draw on studies that did not exist when the first was written.
Different judgement on the same facts
The shared rules leave room for interpretation. Two careful experts can read the same study and weigh it differently.
Common points of difference
- How much to trust a computer prediction
- Whether one small study is enough
- How to read results from laboratory experiments
Different people in the data
Much of the world's genetic data comes from people of European ancestry. A variant that is common and harmless in Indian families can look rare, and so more suspicious, to a laboratory with little Indian data.
This is one reason Indian reference data matters so much.Not sure whether this applies to you?
Ask an oncologistIf your reports disagree
What should you do if two reports say different things?
Do not act on either report alone
Hold off on major decisions, such as preventive surgery or telling relatives they carry a fault, until a specialist has looked at the difference.
Put both reports side by side
Check that both name the same gene, the same version of the gene, called the transcript, and the same variant. Sometimes an apparent disagreement is really two different changes.
Note the date on each
A newer report may simply reflect newer evidence. Ask whether the older laboratory has reviewed the variant since it wrote its report.
Ask your counsellor to contact both laboratories
Laboratories can share evidence with each other and often resolve differences this way. Your counsellor can make that request on your behalf.
Check whether an expert panel has reviewed it
For some well-studied genes, specialist groups publish an agreed classification in public databases such as ClinVar. Where one exists, it usually carries the most weight.
On your report
The words you will meet, in plain language
- Variant classification
- The label a laboratory gives a change in a gene, running from benign, through uncertain, to pathogenic.
- ACMG criteria
- The shared rules most laboratories use to decide that label. They list the kinds of evidence that count for and against harm.
- ClinVar
- A free public database where laboratories post their classifications. It shows at a glance when laboratories disagree.
- Conflicting interpretations
- The phrase ClinVar uses when laboratories have given the same variant different labels.
- Expert panel review
- A classification agreed by specialists in one gene after reviewing all the shared evidence. It outweighs a single laboratory's view.
- Reclassification
- A change to a variant's label after new evidence. It is the usual way a disagreement is eventually settled.
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Side by side
Which disagreements matter, and which rarely do
Rarely changes care
Needs a specialist to look again
Pathogenic against likely pathogenic
Likely pathogenic against uncertain
Benign against likely benign
Uncertain against likely benign, when relatives are waiting
The same label in different wording
Two variant names that may describe the same change
An older report replaced by the same laboratory
Any disagreement before a decision on preventive surgery
Being straight with you
What this page cannot tell you
It cannot tell you which laboratory is right about your variant. That needs someone who can read both reports, see the evidence each one used and check what has been published since. What your specific variant means is a question for the counsellor who ordered the test.
It cannot settle a disagreement for you
Searching for your variant online will often turn up the disagreement itself, listed in a public database, without the reasoning behind it. That can be more worrying than helpful. A counsellor can see why each laboratory reached its view, and can ask them to compare notes.
Who this does not apply to
If you have a single report and nobody in the family has been tested elsewhere, there is nothing to reconcile. This page also does not cover tumour testing, which classifies changes for a different purpose and is covered on our targeted therapy pages.
If relatives were tested at different laboratories, keep copies of every report together. It makes a disagreement far easier to spot and to sort out.Commonly believed
Four things families believe when labs disagree
"One of the laboratories must have made a mistake."
Usually neither did. Each read the evidence in front of it using the same rules. The difference usually comes from what evidence each laboratory had, or when it looked.
"The more expensive test must be the right one."
Price reflects the size of the panel and the service, not the quality of one classification. A laboratory with strong data on a particular gene can be more reliable for that gene than a larger one without it.
"The worse label is the safe one to follow."
Acting on a harmful label that turns out to be wrong can lead to surgery nobody needed, and to relatives being told they carry a fault. Caution means getting the classification right, not assuming the worst.
"If the labs disagree, the variant will never be understood."
Most disagreements settle with time. As more families are tested and laboratories share data, classifications tend to move towards agreement. Your counsellor can tell you if yours does.
Questions we are asked
Common questions about labs that disagree
How common are disagreements between laboratories?
Common enough that public databases track them. Most involve small steps, such as pathogenic against likely pathogenic, which rarely change care. Disagreements across the line between uncertain and harmful are less common, and those are the ones worth a specialist's attention.
Which report should I believe?
Neither on its own. A newer report, one backed by an expert panel, or one from a laboratory with a long record on that gene may carry more weight. Your counsellor can weigh these for your specific variant and tell you which view the evidence supports.
Can I ask a laboratory to review its classification?
Yes, usually through the doctor or counsellor who ordered the test. Laboratories will often look again when shown new evidence, such as another report, a published study, or information about how the variant travels in your family.
Can my family history help settle the question?
It can. If the variant is found in several relatives who developed cancer, and is missing in those who did not, that pattern is evidence a laboratory can use. Your counsellor may ask whether relatives are willing to be tested for this reason.
Should I delay surgery until the labs agree?
If a preventive operation is being considered because of a disputed variant, it is reasonable to ask for the disagreement to be reviewed first. A decision like this should rest on a classification the specialists are confident in. Discuss the timing with your surgeon and counsellor together.
My relative's report says pathogenic and mine says uncertain. What now?
First check that both reports describe exactly the same variant. If they do, your counsellor can contact both laboratories. Until it is resolved, most specialists plan care from the evidence and your family history rather than from either label alone.
Are disagreements more likely because we are Indian?
They can be. Global databases hold far less data from Indian families, so some variants that are common and harmless here look rare elsewhere. Laboratories with Indian data help, and the gap is slowly narrowing as more families here are tested.
Who can help me make sense of two different reports?
A genetic counsellor or clinical geneticist, who can read both reports and talk to both laboratories. Bring both full documents, not a summary. Call the CION helpline if you are not sure who to approach, and someone will point you to the right clinic.
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)
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Sources
- American College of Medical Genetics and Genomics — Standards and guidelines for the interpretation of sequence variants
- ClinVar (NCBI) — ClinVar: public archive of variant classifications
- ClinGen — ClinGen: Clinical Genome Resource
- MedlinePlus Genetics — What do the results of genetic tests mean?
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
The five variant classifications explainedThe labels laboratories are disagreeing aboutVariant reclassification: when a result changes years laterHow most disagreements are eventually settledClinVar and looking up your own variantWhere conflicting labels show up in publicHaving a report reinterpreted elsewhereWhen a second opinion on the variant makes sense
Talk to us
Two reports, two different answers?
Bring both reports and tell us who in the family was tested where. We will help you reach a counsellor who can compare them properly. One helpline serves every CION centre.