Serum myoglobin test
A serum myoglobin test is used to measure the level of myoglobin in blood. Myoglobin is a protein that’s typically found in heart and skeletal muscle tissues. 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. When detected through a blood test, the presence of myoglobin is clinically significant.
Why is serum myoglobin test ordered?
Your doctor may order this test if they think you’re having a heart attack. Most of the time, heart attacks are obvious, based on symptoms and family history. There are times, however, when a heart attack is not outwardly clear. Serum myoglobin levels may be elevated in cases of inflammatory and degenerative muscle diseases and following muscle injury. This can help your healthcare provider make a diagnosis.
A serum myoglobin test may also be ordered if you have symptoms of kidney disease or kidney failure.
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 0 to 85 nanogram per milliliter (ng/mL). Normal results will allow your doctor to rule out a heart attack.
Abnormal (above 85 ng/mL) results can also be seen in:
- muscular inflammation (myositis),
- muscular dystrophy (hereditary disorders that cause muscle wasting and weakness),
- rhabdomyolysis (breakdown of muscle tissue from prolonged coma, certain drugs, inflammation, prolonged seizures, and alcohol or cocaine use).
A doctor may suggest additional tests to reach a diagnosis if your results are outside of the normal range.
Serum troponin test
The serum myoglobin test has, for the most part, been replaced by the serum troponin level test. The troponin level test can provide a positive diagnosis of a heart attack. This is because troponin levels are more specific to heart damage than myoglobin levels. Troponin levels will also stay higher than myoglobin levels for longer time periods, when there’s a heart attack.
A serum troponin test measures the level of troponin proteins (specifically Troponin I or T) in your blood. Troponin normally resides in heart muscle cells, so detecting it in the blood indicates heart muscle damage. It is the primary blood test used to quickly diagnose heart attacks.-
- Diagnosing Heart Attacks: It helps confirm if chest pain or other symptoms are due to a heart attack.
- Evaluating Heart Damage: Higher troponin levels correlate with the extent of damage to the heart muscle.
- Monitoring: Doctors frequently repeat the test over 6 to 24 hours to track if heart injury is ongoing or resolving.
- Other Conditions: Elevated troponin can also indicate other cardiac issues such as heart failure, myocarditis, or kidney disease.
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- Normal/Healthy Level: Typically, less than 0.04 ng/mL.
- Probable Heart Injury/Heart Attack: Levels significantly above 0.04 ng/mL (often around 0.40 ng/mL or higher) indicate probable myocardial infarction.
- Procedure: A healthcare professional will draw a standard blood sample, usually from a vein in your arm.
- Timing: Because troponin takes a few hours to leak into the bloodstream after a heart injury, the test is often performed upon arrival at the hospital and repeated later.
- Next Steps: Troponin results are almost always interpreted alongside an electrocardiogram (ECG) and a physical examination.
Cardiac biomarkers
Cardiac biomarkers are substances released into the bloodstream when damage to the heart takes place.
A cardiac biomarker test is a blood test that measures specific proteins and enzymes released into the bloodstream when the heart muscle is damaged or stressed. It is primarily used in emergency settings to diagnose heart attacks (myocardial infarction) or evaluate acute coronary syndrome (ACS).
What it Measures
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- Troponin (cTnI and cTnT): The gold standard and most sensitive biomarker. Levels rise within a few hours of heart damage and can remain elevated for up to two weeks.
- Creatine Kinase-MB (CK-MB): An enzyme found primarily in heart muscle. Levels typically rise within 4 to 6 hours after an attack and return to normal in about 2 days.
- Myoglobin: A protein that stores oxygen. It is the first to elevate (within 1 to 2 hours) but is less specific to the heart than troponin.
- BNP (B-type Natriuretic Peptide): Used primarily to evaluate and monitor heart failure rather than heart attacks.
- hs-CRP (High-sensitivity C-reactive protein): An indicator of inflammation used to assess the long-term risk of cardiovascular disease.
Why the Test is Ordered
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- Symptom Evaluation: Ordered if you experience chest pain or pressure, shortness of breath, or pain in the jaw, neck, or arm.
- Monitoring: Used to track how well your heart is recovering after a heart attack or a cardiac procedure (like coronary bypass surgery or angioplasty).
What the Results Mean
Negative results can be used to rule out a heart attack. Positive results don’t confirm that a heart attack has happened, though. In order to definitively diagnose a heart attack, a doctor will look at your troponin levels and have you undergo an electrocardiogram (EKG). An EKG is a test that measures the electrical activity of your heart.
How is the test administered?
The test is typically given in an emergency healthcare setting when a person experiences symptoms of a heart attack. Those admitted to the emergency room with symptoms of a heart attack will likely have the test administered immediately.
The test requires a blood sample. 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 8 to 12 hours. Myoglobin levels typically return to normal within 24 hours. This allows us to compare changes in myoglobin levels, if necessary.
Because the test is often given in emergency situations, it’s unlikely that you’ll be able to prepare for it.
People who have recently experienced an angina attack may have increased myoglobin levels. Additionally, people who have undergone cardioversion (a procedure for restoring heart rhythm back to normal) may also have increased levels of the protein. People who have kidney disease should report this medical issue, because kidney disease will result in high levels of myoglobin in the bloodstream.
Patient should also inform the doctors about any drug and alcohol use. Heavy alcohol consumption and the use of certain drugs can cause muscle injury, which also increases myoglobin levels.