Hemolysis is Not Associated with an Elevation of Serum Myoglobin
The answer is B. Hemolysis is not associated with an elevation of serum myoglobin.
Understanding Myoglobin and Its Elevations
Myoglobin is an oxygen-binding protein synthesized exclusively in striated and cardiac muscle. It is released into circulation when muscle damage occurs, making it a useful early marker for muscle injury. According to the evidence, myoglobin has the following characteristics:
- Low molecular weight (17 kD) 1
- First detectable in serum 1-2 hours after muscle injury 1
- Reaches 100% sensitivity at 4-8 hours 1
- Returns to normal within 24 hours 1
Conditions Associated with Elevated Myoglobin
Electrocution (A)
- Causes direct muscle damage and necrosis
- Results in release of myoglobin from damaged skeletal and cardiac muscle
Muscular Dystrophy (C)
- Patients with progressive muscular dystrophy show markedly elevated myoglobin levels (40-1700 ng/ml) 2
- Particularly high in Duchenne muscular dystrophy
- Reflects ongoing muscle breakdown characteristic of the disease
Acute Myocardial Infarction (D)
Why Hemolysis Does Not Elevate Myoglobin
Hemolysis involves the breakdown of red blood cells, not muscle cells. Since myoglobin is only found in cardiac and skeletal muscle tissue, not in erythrocytes, hemolysis does not cause myoglobin elevation. This is in contrast to other markers that may be affected by hemolysis:
- Red blood cells do not contain myoglobin
- Hemolysis releases hemoglobin, not myoglobin
- Radioimmunoassay studies have confirmed that hemolysis does not affect myoglobin measurements 3, 2
Clinical Significance of Myoglobin Testing
Myoglobin has several important characteristics as a cardiac marker:
- High sensitivity for early detection of MI 1
- Rapid release kinetics make it useful for monitoring reperfusion 1
- Very low specificity in settings of skeletal muscle injury 1
- Rapid return to normal range limits sensitivity for later presentations 1
Comparison with Other Cardiac Markers
| Marker | First Detectable (h) | 100% Sensitivity (h) | Duration (d) | Specificity |
|---|---|---|---|---|
| Myoglobin | 1-2 | 4-8 | 0.5-1.0 | Low |
| Troponin I | 2-4 | 10-24 | 5-10 | High |
| Troponin T | 3-4 | 8-12 | 5-14 | High |
| CK-MB | 3-4 | 10-24 | 2-4 | Moderate |
Common Pitfalls in Interpreting Myoglobin Elevations
- False positives: Any skeletal muscle injury can cause myoglobin elevation
- Timing: Myoglobin levels return to normal quickly, so late presentations may have normal levels despite MI
- Renal dysfunction: Reduced clearance can cause elevated myoglobin without new muscle injury
- Exercise: Strenuous exercise can cause transient myoglobin elevation
In summary, while myoglobin is elevated in conditions involving muscle damage (electrocution, muscular dystrophy, and AMI), it is not elevated in hemolysis since red blood cells do not contain myoglobin.