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Reading your BCR-ABL report and the IS scale | CION Cancer Clinics
The IS percentage on a BCR-ABL report shows how much of the CML gene is left in your blood compared with a standard untreated level of 100%. Lower is better. 1% means about a hundredfold fall, and 0.1% or lower is called major molecular response. One result is read as part of a trend, never on its own. Here is how to read each line. At CION Cancer Clinics, every leukaemia, MDS and MPN case is reviewed by our haematologist and discussed at a tumour board before a plan is agreed.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- What does the IS percentage on a BCR-ABL report mean?
- How do you read the report, line by line?
- Which terms on the report need a plain meaning?
- Why can your number go up or down between tests?
- What does each IS level usually correspond to?
- What do people often misread on a BCR-ABL report?
- What can one BCR-ABL result not tell you?
- Common questions about BCR-ABL reports
The short answer
What does the IS percentage on a BCR-ABL report mean?
The IS percentage shows how much BCR-ABL, the gene that drives CML, is left in your blood compared with a standard untreated level. Lower is better: 0.1% or less is called a major molecular response, and it is a key target of treatment.
What IS stands for
IS means International Scale. Different laboratories use different machines and methods. The International Scale adjusts each lab's raw result so that a number from one accredited lab can be compared with a number from another. Think of it as converting every result into one shared currency.
Why a smaller number is the goal
On the International Scale, 100% stands for the typical amount of BCR-ABL in people with untreated CML. As the tablet works, the amount falls. A result of 1% means about a hundredth of that starting level is left. A result of 0.1% means about a thousandth is left.
Why one result is never read alone
The test is extremely sensitive, so small ups and downs are normal. Your haematologist looks at the trend across several reports, the time since you started treatment, and whether you have been taking the tablet every day.
If your report shows a percentage without the letters IS, ask the laboratory whether it is on the International Scale. A non-IS number cannot be compared with the targets below.Line by line
How do you read the report, line by line?
Test name and method
Look for words like quantitative RT-PCR or qPCR for BCR-ABL1. This is the monitoring test. A qualitative test only says positive or negative, and is used mainly at diagnosis.
Transcript type
Most reports name e13a2 or e14a2, the two common forms of the joined gene. A rarer type may need a different test, so note which you have.
The IS result
This is the headline number, shown as a percentage. Some reports add the molecular response level, such as MR3 or MR4, beside it.
Control gene and comment
The control gene count shows the sample was good enough to trust. Read the lab comment too. It may say the sample was poor or the result is near the limit.
Not sure whether this applies to you?
Ask an oncologistOn your report
Which terms on the report need a plain meaning?
- BCR-ABL1
- The joined gene that drives CML. The test counts how much of its message is in your blood.
- Log reduction
- Each log is a tenfold drop from the standard starting level. A 3-log reduction is a thousandfold drop.
- MMR or MR3
- Major molecular response. The result is 0.1% IS or lower.
- MR4 and MR4.5
- Deeper responses, at 0.01% and 0.0032% IS or lower. Often called deep molecular response.
- Undetectable
- No BCR-ABL was found in this sample. It does not mean CML has gone, only that it is below what the test can see.
- ABL1 or GUSB copies
- The control gene. Too few copies means the sample may not be reliable.
Before you worry
Why can your number go up or down between tests?
A change is worth discussing. It is not always a sign that treatment is failing.
Normal test wobble
At very low levels, the test is counting a tiny number of copies. A small rise, such as from 0.02% to 0.04%, can simply be the test being imprecise.
A different laboratory
Even on the International Scale, labs are not identical. Moving between labs can shift results a little. Staying with one accredited lab keeps your trend easier to read.
Missed or late doses
Missing tablets is one of the commonest reasons for a rise. Be honest with your team about gaps. They are there to help, not to judge.
Also check
- New medicines or herbal products
- Changes in how you take the tablet
A real change in the disease
Sometimes a rise is genuine, for example from a gene mutation that makes the tablet work less well. A repeat test usually comes first, then further tests if the rise is confirmed.
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At a glance
What does each IS level usually correspond to?
IS result
What it is usually called
10% or lower
About a tenfold fall. An early sign the tablet is working
1% or lower
About a hundredfold fall. Close to what older tests called complete cytogenetic response
0.1% or lower
Major molecular response, also written MMR or MR3
0.01% and 0.0032% or lower
Deep molecular response, written MR4 and MR4.5
Commonly believed
What do people often misread on a BCR-ABL report?
"The percentage is how much of my blood is cancer."
It is not. The number compares the gene message in your sample with a standard untreated level. A result of 1% does not mean one in a hundred of your blood cells is leukaemia.
"It went from 0.01% to 0.02%, so the CML has doubled."
At such low levels, the test can easily move this much by chance. Your team looks for a rise that is repeated and meaningful, not a single small step.
"Undetectable means I can stop the tablet."
Some people do stop under a planned programme, but only after deep responses held for years, with frequent testing. Stopping on your own risks the disease coming back.
"Any lab result is as good as another."
A result without the International Scale, or from a lab with few control copies, can mislead. Ask your team which lab they trust, and try to stay with it.
Being straight with you
What can one BCR-ABL result not tell you?
A single result cannot tell you whether treatment is failing, or how long you will do well. It is a snapshot. Its meaning depends on how long you have been on treatment and on the results before it.
The same number means different things at different times
A result of 1% can be good news early in treatment and a reason to look closer much later. That is why haematologists set time-based milestones in the first year, and why this page does not judge your result for you.
Who the IS scale does not suit
People with a rare transcript type may not get a reliable IS result from the standard test. Their team may use a different method, and the usual milestones may not apply in the same way.
What to bring to your review
Bring every BCR-ABL report in date order, with the lab name. CION's haematology team will read them as a trend and explain what they show. The test itself is done by accredited laboratories.
Questions we are asked
Common questions about BCR-ABL reports
My BCR-ABL is 0.1% IS. Is that good?
It is the level called major molecular response, which is a key treatment target. Whether it is good for you depends on when it was reached and whether it holds on repeat tests. Your haematologist reads it alongside your earlier results and how long you have been taking the tablet.
Why is my result given as a ratio or copies, not a percentage?
Some labs report the raw ratio of BCR-ABL to the control gene, then convert it to IS. If only a ratio appears, ask whether the lab reports on the International Scale. Without that, the number cannot be compared to standard targets.
How often is the BCR-ABL test done?
More often in the first year, and at regular intervals after that once results are stable. The exact gap is set by your haematologist. It may be shortened if a result rises or if you change tablets. Keep to the schedule even when you feel well.
Can I test at any lab near my home?
It is better to use one lab that reports on the International Scale and that your team trusts. Changing labs often makes small shifts hard to interpret. If travel is difficult, ask your team whether a sample can be sent from a collection centre near you.
My result went up slightly. What happens now?
Usually a repeat test first, sometimes sooner than planned. Your team will ask about missed doses, new medicines and side effects. If the rise is confirmed and significant, they may check for gene mutations. Keep taking your tablet as prescribed unless your team tells you otherwise.
Does undetectable mean my CML has gone?
Not quite. It means the level is below what that test can measure in that sample. Leukaemia cells can still be present. It is a very good result, and it is one of the steps toward a possible planned stop in the future.
Do I need to fast before a BCR-ABL test?
Usually not. It is a blood sample in a special tube. What matters more is that the sample reaches the lab quickly, because the gene message breaks down over time. Ask the collection centre how and when it will be sent.
Is the BCR-ABL test covered by schemes?
Often, as part of an approved CML treatment plan. Aarogyasri, CGHS, ECHS, EHS, PM-JAY and cashless insurance may cover monitoring tests, depending on current rules. Entitlements change, so check yours. Call the helpline and we will help you find out.
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Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- Leukemia & Lymphoma Society — Chronic Myeloid Leukemia
- National Cancer Institute — Chronic Myelogenous Leukemia Treatment (PDQ) - Patient Version
- Cancer.Net — Leukemia - Chronic Myeloid - CML
- Cancer Research UK — Chronic myeloid leukaemia (CML)
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
Major Molecular Response ExplainedWhat reaching 0.1% means for youCML Treatment Milestones at 3, 6 and 12 MonthsThe targets your result is compared againstBCR-ABL Mutation Testing After TKI FailureThe next test if your level keeps risingCML Explained: A Cancer Managed Like a Chronic IllnessThe basics of CML in plain words
Talk to us
Have a BCR-ABL report you are unsure about?
Send us your reports in date order. Our haematology team will read them as a trend and explain what they show. One helpline serves every CION centre.