What is a Serum Myoglobin Test?
Serum myoglobin is a blood test that is used to measure the levels of myoglobin in the bloodstream.
Myoglobin is a protein that is commonly found in the heart and skeletal muscles. The only time that myoglobin is found in the bloodstream is when injury to a muscle has occurred. In particular, injury to the heart muscle results in the release of myoglobin. Thus, when detected through a blood test, the presence of myoglobin is clinically significant.
Why Is the Test Ordered?
This test is typically ordered when it is suspected that a patient is having a heart attack. Most of the time, heart attacks are obvious. However, in some cases, a heart attack is not outwardly clear. Serum myoglobin can be elevated in cases of inflammatory and degenerative muscle diseases and following muscle trauma.
Serum myoglobin test has, for the most part, been replaced by the troponin level test to provide a positive diagnosis of a heart attack. This is because troponin levels are more specific to heart damage than myoglobin levels. Additionally, troponin levels will stay higher than myoglobin levels for longer when there is a heart attack.
However, serum myoglobin is still used in some cases. The test is commonly ordered in conjunction with other tests for cardiac biomarkers (substances released into the bloodstream when damage to the heart takes place). These other tests include: troponin, creatine kinase (CK), and creatine kinase-MB (CK-MB). Negative results obtained from a myoglobin test can be used to rule out a heart attack. However, positive results do not confirm that a heart attack has indeed occurred. In order to diagnose a heart attack, troponin levels must also be measured.
The serum myoglobin test may also be ordered following the diagnosis of a heart attack. Once damage to the heart muscle has been confirmed, values obtained from the serum myoglobin test can help physicians estimate the amount of muscle damage that has occurred. Serum myoglobin may also be ordered if the patient has symptoms of kidney disease or kidney failure.
How Is the Test Administered?
The test is typically administered in an emergency healthcare setting when a patient experiences symptoms of a heart attack. Patients admitted to the emergency room with symptoms of a heart attack will likely have the test administered immediately. The test requires a blood sample, which is taken by a health care provider after the site of entry of the needle on the inside of the elbow or the back of the hand is cleaned with an antiseptic.
An elastic band is tied around the arm, which slows the flow of blood, allowing the veins to fill with blood. The blood is drawn into a tube that is connected to the needle and sent to the laboratory for analysis. The elastic band is then released and a cotton ball or gauze is used to apply pressure to the site of entry.
If it is to be used, this test should be performed every two to three hours for up to 12 hours following admission. Serum myoglobin levels begin to increase within two to three hours following a heart attack. These levels reach their highest values within eight to 12 hours. Myoglobin levels typically return to normal within 24 hours. Thus, use of the myoglobin-serum test allows the physician to compare changes in myoglobin levels.
Preparation for the Test
Since the test is often given in emergency situations, it is unlikely that you will be able to prepare for the test.
However, if possible, you should tell your healthcare provider about recent health issues and testing you have undergone.
Patients that have recently experienced an angina attack may have increased myoglobin levels. Additionally, patients that have undergone cardioversion—a procedure for restoring heart rhythm back to normal—may also have increased levels of the protein. Patients that have kidney disease should report this medical issue, because kidney disease will result in high levels of myoglobin in the bloodstream. Patients should also inform providers about any drug and alcohol use. Heavy alcohol consumption and the use of certain drugs can cause muscle injury, which also increases myoglobin levels.
What Are the Risks of the Test?
The serum myoglobin test carries minimal risks for the patient. The risks of the test are common to all blood tests and include the following:
- difficulty obtaining a sample, resulting in the need for multiple needle sticks
- excessive bleeding at the needle site
- fainting as a result of blood loss
- the accumulation of blood under the skin, known as a hematoma
- development of infection where the skin has been broken by the needle
What Do The Results Tell Us?
The range of normal results for the serum myoglobin test will vary slightly based on the laboratory completing the analysis. In most instances, the normal or negative range for the serum myoglobin test is zero to 85 ng/mL. Normal results will allow the physician to rule out a heart attack
Abnormal results can also be seen in:
- muscular inflammation (myositis)
- muscular dystrophy (hereditary disorders that have muscles wasting and weakness)
- rhabdomyolysis (breakdown of muscle tissue from i.e. prolonged coma, drugs, inflammation, prolonged seizures, alcohol and cocaine use)