Diagnosing Hemophilia in Children

Hemophilia is a blood disorder that prevents blood from clotting properly. Normally, blood cells known as platelets clump together to plug a hole or tear caused by a cut or other injury to the body. Platelets release chemicals that tell the body to make proteins called clotting factors, which mix with platelets to strengthen clots and stop bleeding. 

Hemophilia is caused by changes, or mutations, in one of two genes—F8 and F9—that make clotting factors. Changes in the F8 gene lead to a reduction in the amount of factor VIII, whereas mutations in the F9 gene decrease the amount of factor IX. In hemophilia type A, which is more common, people have little or no factor VIII. Those with hemophilia type B have little or no factor IX. Thousands of possible genetic mutations of the F8 and F9 genes can affect the production of these clotting factors. 

Most children with hemophilia have inherited an abnormal gene from a parent. But about one-third of people with hemophilia develop a genetic mutation spontaneously. The severity of symptoms depends on the mutation and how much clotting factor a person’s body makes.   

Hemophilia occurs mainly in boys, who can develop the condition if they have a single abnormal gene. Boys have only one X chromosome, which is where the genetic mutations that cause hemophilia occur. Girls have two X chromosomes, so if one chromosome contains an abnormal gene, the normal gene on the other chromosome can usually compensate. Girls can develop hemophilia if they have two abnormal genes, which is very rare. 

Doctors may suspect hemophilia if a newborn has excessive bleeding during medical procedures that are commonly performed after birth, such as circumcision or a blood draw to screen for other conditions. Children with hemophilia do not bleed faster than other children, but they bleed for a longer period of time.

The most common symptoms of hemophilia are pain and swelling, which are caused by bleeding into spaces within the joints or into muscles. Other symptoms include raised bruises, nosebleeds, bleeding in the mouth after tooth brushing, and blood in urine or stool. Without treatment, people with hemophilia may develop joint damage from recurrent bleeding into the joints. Others may develop bleeding in the brain, which can cause a stroke. 

Parents may first notice symptoms when a child begins crawling or walking, which can lead to large bruises, swollen joints, or refusal to use a painful arm or leg. A mouth injury or routine dental care, which usually begins during toddlerhood, may also bring symptoms to light. 

Doctors at NYU Langone can diagnose the condition while a child is in the womb, or during infancy or childhood. If you’re planning a pregnancy, you and your partner may consider genetic testing if you have a family history of hemophilia. 

Prenatal Genetic Tests

Numerous genetic mutations can cause hemophilia. However, doctors only perform prenatal tests for hemophilia, such as amniocentesis or chorionic villus sampling, after they identify a specific genetic mutation in a parent or a close relative with the condition. NYU Langone genetic counselors can help you understand the results of these tests.


In amniocentesis, the doctor inserts a hollow needle through a pregnant woman’s abdomen and into the uterus, or womb, removing a small amount of the amniotic fluid that surrounds the baby. The doctor sends the fluid sample to a specialized laboratory, where it is examined to look for the family member’s genetic mutation. Amniocentesis is usually performed early in the second trimester of pregnancy.

Chorionic Villus Sampling

Chorionic villus sampling can be performed after the 11th week of pregnancy. During this test, the doctor threads a thin tube through the vagina and cervix and into the placenta—a temporary organ that delivers oxygen and nutrients to an unborn child—to remove a small amount of tissue. The tissue sample is sent to doctors at a specialized laboratory, who look for the family member’s genetic mutation.

Physical Exam

During a physical exam, the doctor asks you for a detailed account of any symptoms you may have noticed in your child, such as nosebleeds, unusual bruises, or blood in the urine or stool. The doctor also examines your child for raised bruises or swelling around the joints, and to see how much movement your child has in the joints. 

Blood Tests

Doctors use blood tests to screen for and confirm a diagnosis of hemophilia. One preliminary blood test, called partial thromboplastin time, measures the amount of time it takes for a sample of your child’s blood to clot. Children with a longer-than-usual clotting time may not have enough clotting factors. Results of this test, which is performed in the doctor’s office, are usually available on the same day.

Another blood test measures the amount of clotting factors VIII and IX in your child’s blood. The more a child has, the better the blood is able to clot. For children who have family members with unusually heavy menstrual periods, blood tests may also be used to measure levels of von Willebrand factor, another protein involved in clotting. Doctors can confirm a diagnosis of hemophilia and determine the severity of the condition based on the levels of these factors. 

Information from these tests helps doctors understand the severity of hemophilia and develop an appropriate treatment plan.

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