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Mild, moderate or severe haemophilia: what your factor level means | CION Cancer Clinics
Haemophilia severity depends on how much working clotting factor your blood makes. Under 1% of normal is severe, 1% to 5% is moderate, and above 5% up to about 40% is mild. The lower the level, the more easily bleeds start, sometimes with no injury at all. This page explains what each level usually means, how it is measured, and what the label alone cannot tell you. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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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 do mild, moderate and severe haemophilia mean?
- How does bleeding usually differ at each level?
- How is the factor level measured and confirmed?
- What do the words on a factor report mean?
- Why do two people with the same level bleed differently?
- What do families often get wrong about severity?
- What can the severity label not tell you?
- Common questions about haemophilia severity
The short answer
What do mild, moderate and severe haemophilia mean?
Severity is set by one number: how much working clotting factor your blood makes, compared with a healthy person. Under 1% is severe, from 1% to 5% is moderate, and above 5% up to about 40% is mild.
What the percentage is measuring
Clotting factors are proteins that help blood form a firm clot. In haemophilia A the missing one is factor VIII. In haemophilia B it is factor IX. The laboratory measures how well your factor works, then gives it as a share of normal. Most healthy people sit somewhere between 50% and 150%.
Why the level matters so much
The lower the level, the less it takes to start a bleed. With a very low level, bleeds can begin inside a joint or muscle with no injury you can remember. With a higher level, bleeding usually follows a cut, a fall, a tooth removal or an operation, and may simply last longer than it should.
The level usually stays the same for life
Haemophilia is passed down in the genes, so the factor level you are born with rarely changes on its own. Your severity label is therefore usually settled once and carried through childhood into adult life.
Reference ranges differ between laboratories. Your result is read alongside your bleeding history and a repeat test, never on its own.Level by level
How does bleeding usually differ at each level?
These are typical patterns, not rules. Your own bleeding history counts as much as the number on the report.
Severe: under 1%
Often found in the first year or two of life, when a baby starts crawling and bruises appear easily. Bleeds into joints and muscles can happen without any clear injury.
Often seen
- Swollen, warm, painful knees, ankles or elbows
- Large bruises from small knocks
- Long bleeding after a tooth comes out
Moderate: 1% to 5%
Bleeds usually follow a minor injury rather than coming on by themselves, though some people at the lower end behave more like severe haemophilia.
Often seen
- Joint bleeds after a twist or fall
- Heavy bleeding after surgery or dental work
Mild: above 5%
Many people go years without knowing. It is often found only when bleeding after an operation, a circumcision or a tooth removal will not settle.
Mild does not mean harmless. A serious injury or surgery can still cause dangerous bleeding.Not sure whether this applies to you?
Ask an oncologistGetting the number
How is the factor level measured and confirmed?
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A bleeding history
The haematologist asks about bruising, joint swelling, bleeding after injections or teeth, and whether any male relatives on the mother's side had similar problems.
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A basic clotting screen
A blood test checks how long your blood takes to clot. In haemophilia one of these clotting times is often longer than normal, but in mild cases it can look normal.
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A factor assay
A specific test measures factor VIII or factor IX activity. This is the test that gives the percentage and the severity label.
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A repeat test
Stress, illness, pregnancy and a difficult blood draw can change the result. A borderline level is usually checked again before the label is confirmed.
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A gene test, where available
This finds the exact change in the gene. It helps with carrier testing for sisters, daughters and mothers, and sometimes hints at the risk of inhibitors.
On your report
What do the words on a factor report mean?
- Factor VIII:C or FVIII activity
- How well your factor VIII works, given as a percentage of normal or in IU/dL. The two numbers mean the same thing.
- Factor IX activity
- The same measurement for haemophilia B.
- aPTT
- A general clotting time. A long aPTT points towards a factor problem but does not say which one.
- One-stage and chromogenic assay
- Two laboratory methods for measuring factor. They can give slightly different results, so a change of laboratory can change the number.
- Inhibitor
- An antibody that blocks the factor given as treatment. It is tested for separately and is not part of the severity label.
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Beyond the label
Why do two people with the same level bleed differently?
The factor level predicts bleeding well, but not perfectly. Two brothers with the same result can have quite different lives, and your treatment plan is built on how you actually bleed, not on the label alone.
Joints that have bled before bleed more easily
A joint that has had repeated bleeds becomes inflamed and fragile. It can then bleed with less and less trigger. Someone with moderate haemophilia and a damaged knee may bleed as often as someone with severe haemophilia.
Activity, age and other genes play a part
Sport, heavy physical work, body weight and other inherited clotting traits all shift the pattern. Children often bleed differently as they grow and become more active.
Who the label does not describe well
Girls and women who carry the gene are a common blind spot. Some have factor levels in the mild range and real bleeding problems, especially heavy periods and bleeding after childbirth, yet are told they are only carriers.
Commonly believed
What do families often get wrong about severity?
"He has mild haemophilia, so we do not need to tell the dentist."
Mild haemophilia is often first discovered because a tooth removal or small operation bled for far too long. Every dentist and surgeon should know before they start, and the haematology team should plan the procedure with them.
"Girls cannot have haemophilia, only carry it."
Many carriers have lower factor levels than expected, and some fall in the mild haemophilia range. A woman with heavy periods or unusual bleeding in a family with haemophilia should have her own factor level checked.
"Severe haemophilia will get milder as he grows up."
The factor level is set by the gene and does not rise with age. What can change is how well bleeds are prevented and treated, which shapes how healthy the joints stay.
"One test result settles it for good."
A single result can be affected by illness, stress or how the sample was handled. A borderline or surprising number is usually repeated before it changes anything.
Being straight with you
What can the severity label not tell you?
The label tells you how much factor your blood makes. It does not tell you which treatment you need, how your joints will be in later life, or whether you will develop an inhibitor. Those depend on how bleeds are prevented and treated over the years.
It does not decide the treatment on its own
People with severe haemophilia are usually offered regular preventive treatment. People with moderate or mild haemophilia may be treated only when a bleed happens, or before surgery. Your haematologist weighs the label against how often you bleed and how active you are.
What to bring to the appointment
Bring every factor report you have, any record of bleeds, and the family history on the mother's side. At CION, Dr. Basudev Pokhrel and the haematology team review these together and help you plan treatment and access to factor through the right centre and scheme.
Any head injury, severe headache, or bleeding that will not stop in a person with haemophilia needs the nearest emergency department now, whatever the severity. Call 108 if you need to.Questions we are asked
Common questions about haemophilia severity
My son's report says factor VIII is under 1%. What does that mean?
It means his blood makes almost no working factor VIII, which is called severe haemophilia A. Bleeds into joints and muscles can happen without an injury you notice. It is a serious result, but it is well understood. A haematologist will confirm it and talk to you about regular preventive treatment.
Can the severity change over time?
The level itself is set by the gene and rarely changes. Results can look different between tests because of illness, stress, pregnancy or a change of laboratory method. How someone bleeds can change too, especially once a joint has been damaged. That is why the history matters as much as the number.
Is mild haemophilia something we can ignore?
No. Day to day it may cause few problems, but a serious injury, an operation or a tooth removal can still bleed dangerously. Carry a card or letter that states the diagnosis and level, and make sure every doctor and dentist knows before any procedure.
Why is my daughter being tested if she is only a carrier?
Some carriers have low factor levels and bleed more than expected, particularly with periods, after childbirth or after surgery. Knowing her own level lets the team plan safely for those events. It also helps her understand the chance of passing the gene on, if she wants that information.
Does severe haemophilia always mean joint damage?
Not always. Joint damage builds up from repeated bleeds. When bleeds are prevented or treated quickly, joints can stay in much better shape. The earlier a regular treatment plan starts and the more steadily it is followed, the better the joints usually do over the years.
Are the percentage and IU/dL the same thing?
Yes. The factor level can be reported either way and the numbers match. A result written as a percentage of normal and a result in IU/dL describe the same activity. If two reports from different laboratories disagree, ask your haematologist which method each one used.
Does severity tell us if he will get an inhibitor?
Not on its own. Inhibitors are more common in severe haemophilia A, and the exact gene change also affects the risk, but many people with severe haemophilia never develop one. Inhibitors are checked with a separate blood test, usually during the early treatment period and whenever treatment seems to stop working.
What should we do if he hits his head?
Treat any head injury as an emergency, whatever his severity and even if he seems fine. Go to the nearest emergency department or call 108, say he has haemophilia, and carry his factor card or report. Bleeding inside the head can start slowly, so do not wait for symptoms.
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Sources
- National Heart, Lung, and Blood Institute — Hemophilia
- NHS — Haemophilia
- American Society of Hematology — Hemophilia
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
Haemophilia Explained: A and BStart here if the diagnosis is newFactor Replacement Therapy ExplainedHow the missing factor is given backRegular Treatment vs Treating Bleeds as They HappenWhich approach suits each severityCarrier Testing and Family Planning in HaemophiliaWhy sisters and daughters may need their own level checkedBleeding Disorders and HaemophiliaThe full guide to bleeding disorders
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Tell us what has been found so far. CION's haematology team will read the report with you and explain the next step. One helpline serves every CION centre.