There are a number of blood tests your doctor may choose. The following is a list of some of these. Unless otherwise noted, all of these tests require taking a sample of blood by using a needle. Only a small amount of discomfort and bruising should occur.
Aldolase is a substance found especially in the muscles. When muscles are damaged, the muscle cells break open and spill their contents (including aldolase) into the blood. Therefore, the amount of aldolase in the blood shows the extent of muscle damage. As the muscle damage becomes worse, the amount of aldolase in the muscle decreases over time.
Since muscle weakness can be due to a neurological or a muscular problem, this test finds which is causing the weakness. Aldolase will not change when weakness is caused by neurological problems.
To prepare for this blood test, you should stay away from heavy exercising and have nothing to eat or drink (besides water) for about 8 hours leading up to the test. Follow all of your doctor's orders regarding preparing for the test.
The normal range of results depends on the method used to measure the aldolase level. If you are unsure what the results of this test mean for you, check with your doctor.
Antinuclear Antibodies Test
(Also known as ANA Test)
Antibodies are an important part of our immune system. They fight infections, viruses and other "invaders." Antinuclear antibodies (ANA) are found in the blood of those patients whose immune systems are more likely to fight their bodies' own tissues, or those with autoimmune diseases.
For an ANA test, the lab technician will take a blood sample. The patterns of the ANAs in the blood don't prove the patient has a particular autoimmune disease. Specific patterns may be more common in one disease over another, but more tests would confirm this.
Creatine Phosphokinase Test
(Also known as CPK, Creatine Kinase, or CK Test)
CPK, also known as creatine kinase, or CK, is a type of protein called an enzyme. It helps a reaction to occur. The normal function of CPK in our cells is to turn creatine into phosphate, which is burned as a quick source of energy by our cells.
When muscle is damaged, muscle cells break open and spill their contents into the bloodstream. Because most of the CPK in the body normally exists in muscle, a rise in the amount of CPK in the blood indicates that muscle damage has occurred, or is occurring. The type of CPK found in the blood determines what has been damaged (i.e. heart, brain, muscle).
CPK tests are used to evaluate suspected myositis when other symptoms are not present, to tell whether you have myositis or another neuromuscular disorder, or to check the progress of your disease after treatment.
For this test, a blood sample is taken, a procedure that may be repeated over a period of time for more accurate results. For this reason, if you're scheduled to have blood drawn for a CPK test, you should limit your exercise to normal activities before the test. Certain medicines may also affect the results of the test, so be sure to check with your doctor if you are taking any type of medications at all, including aspirin.
In a healthy adult, the CPK level in the blood serum varies with a number of factors (gender, race and activity), but normal range is 22 to 198 U/L (units per liter). Higher amounts of serum CPK can indicate muscle damage from chronic disease or acute muscle injury.
If the CPK test indicates muscle damage, more tests will be needed to find exactly where the muscle damage occurred.
Myositis patients often question why they may feel better or worse than their CPK levels indicate. The reason for that is the levels may lag behind the improvement or worsening of the disease. Please discuss any questions you have about blood tests with your doctor.
(Also called ESR, or erythrocyte sedimentation rate)
The sed rate, or erythrocyte sedimentation rate, is another method for measuring swelling and inflammation of the muscles. Doctors use the sed rate to watch the progress of the muscle inflammation. This test is not specific to a particular disease but to the presence of the inflammation.
For this test, the technicians mix red blood cells from the blood sample in a prepared test tube. They measure the length of time it takes these cells to settle to the bottom of the tube. For males, the normal rate falls between 0 and 15 millimeters per hour; females, 0 to 20 millimeters per hour. The sed rate will be higher with more inflammation. (The sed rate may be slightly higher if you are older or if you are pregnant.)
Other Blood Tests
- Alanine aminotransferase (ALT, also called serum glutamate pyruvate transaminase [SGPT]) is an enzyme found in many tissues, including muscle. Normal ranges vary by age, gender, and other factors.
- Aspartate aminotransferase (AST, also called serum glutamic-oxaloacetic transaminase [SGOT]) is a protein found in muscle and liver tissue.
- Factor VIII-related antigen (also called von Willebrand factor VIII-related antigen) shows damage to the lining of the blood vessels and helps doctors check the level of the problem, especially in juvenile myositis (JM), to decide the right treatment plan.
- Flow cytometry looks at a specific group of white blood cells and is used to learn more about the extent and severity of juvenile myositis (JM).
- Lactate dehydrogenase is an enzyme found in skeletal muscle tissue. Normal values vary, but typical values range from 105 to 333 IU/L (international units per liter).
Updated February 2014