Blood tests are used to help diagnose and monitor a child's JIA and can help the doctor determine the type of JIA they have. Blood tests are also used to monitor side effects. Blood tests are also referred to as blood work.
How are blood tests done?
Blood tests are done at a lab or blood work clinic. Your child will need to have blood taken with a needle at the lab or clinic.
The person who is trained to take blood is called a phlebotomist. First, they will roll up your child's sleeve. Then they will tie an elastic band around the arm, above the area where the blood will be drawn. The phlebotomist will rub alcohol on your child's skin where the needle will be inserted.
Your child's blood will be drawn into small, airtight tubes called vials. The elastic will be removed when enough blood is taken to let the blood flow normally. It won’t take very long to draw the blood. When the phlebotomist is finished drawing blood, they will take out the needle. They will put a cotton swab and pressure on the spot where the needle entered the skin. This is done to stop the bleeding. Then they will put on a bandage. The vials will be labelled and sent away for analysis.
For some blood tests, only a finger prick is needed.
How to cope with needle pain
Most people don’t enjoy getting blood samples taken, but a few people find it very difficult and stressful. If your child has trouble with needles or blood, topical anaesthetics can be placed on the skin to numb it. There are also some distraction techniques you and your child can use to take their mind off the needle.
You can also talk to your child's doctor or nurse. They can provide you and your child with ways to reduce the pain from blood work.
What are the common blood tests in JIA?
Below are some common blood tests that are done to help diagnose or monitor JIA.
Hemoglobin and blood count testing
This complete blood count (CBC) is a common blood test used to evaluate all the different types of cells in the blood. These include red blood cells (which determine the hemoglobin level), white blood cells and platelets. The test checks for how many cells there are and what the cells look like. If there is anything unusual, the test can help to diagnose many medical conditions.
Erythrocyte sedimentation rate (ESR)
This test checks how rapidly red blood cells settle to the bottom of a test tube. This rate often increases in people who have inflammation occurring anywhere in the body. However, the ESR may not be increased, even if your child has lots of inflammation.
C-reactive protein (CRP)
This test is another measure of the level of inflammation in the body.
Antinuclear antibody (ANA)
The antinuclear antibody (ANA) is a test that looks for certain autoantibodies in the blood. Antibodies are proteins in the immune system, which identify things like bacteria and viruses so the body can fight them off. An autoantibody is an antibody that recognizes parts of the body's own cells as something the body needs to fight. Sometimes, this happens as part of illnesses. The ANA test is positive in:
- About 10% of healthy children and teenagers.
- Some children and teenagers with JIA.
- Most people with certain autoimmune diseases like lupus. An autoimmune disease is when the immune system attacks the body’s own cells.
- Some people with family members who have autoimmune diseases.
The ANA test may also help predict which young people with JIA have an increased risk of eye disease.
Rheumatoid factor (RF)
Rheumatoid factor (RF) is a type of autoantibody produced in the blood in some forms of arthritis. This test is much more commonly found in adults with rheumatoid arthritis. Only about 5% of young people with JIA have a positive RF.
Human leukocyte antigen (HLA)
Human leukocyte antigen (HLA) is a protein in the body. HLA helps the body’s immune system tell the difference between its own cells and foreign substances. For this blood test, the doctor is looking for a specific HLA protein (HLA- B27) on the surface of white blood cells. This protein has been linked with some types of JIA.
Liver and kidney function tests
Testing for the function of the liver and kidney are often done as a general health screen and to get an early, baseline test in preparation for medications, if any are needed.