Unit Converter
Myoglobin
(Early Marker of Muscle Injury - Rapidly Rising Cardiac Biomarker for MI & Rhabdomyolysis)
Synonyms
- Myoglobin
- Mb
- Muscle hemoprotein
- Oxygen-binding muscle protein
- Cardiac & skeletal myoglobin
Units of Measurement
- nmol/L
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- ng/L
- µg/L
Molecular Weight
17,000 Da (17 kDa)
Key Unit Conversions
Mass ↔ Mass Equivalents
1\ \text{ng/mL} = 1\ \text{µg/L} = 1\ \text{ng%} = 1\ \text{ng/100 mL} 1 ng/mL=100 ng/dL1\ \text{ng/mL} = 100\ \text{ng/dL}1 ng/mL=100 ng/dL 1 ng/L=0.001 ng/mL1\ \text{ng/L} = 0.001\ \text{ng/mL}1 ng/L=0.001 ng/mL
Molar ↔ Mass
nmol/L=ng/mL17\text{nmol/L} = \frac{\text{ng/mL}}{17}nmol/L=17ng/mL ng/mL=nmol/L×17\text{ng/mL} = \text{nmol/L} \times 17ng/mL=nmol/L×17
Example:
- 100 ng/mL ≈ 5.88 nmol/L
Description
Myoglobin is a hemoprotein found in cardiac and skeletal muscle.
It rapidly leaks into the bloodstream after muscle injury.
Properties:
- Very early marker for myocardial infarction (MI)
- Rises 2–3 hours after cardiac injury
- Peaks at 6–9 hours
- Returns to normal within 24–36 hours
However:
- Not cardiac-specific
- Elevated in any skeletal muscle damage
Therefore, myoglobin is used in combination with troponin.
Physiological Role
- Stores oxygen in muscle
- Facilitates oxygen diffusion during muscle contraction
- Helps sustain energy during hypoxia
- Released into circulation when muscle cell membranes are damaged
Clinical Significance
HIGH Myoglobin
1. Myocardial Infarction
Very early biomarker:
- Rises in 2–3 hours
- Peak: 6–9 hours
- Normal by 24 hours
Useful to rule out MI when normal at 4–6 hours.
2. Rhabdomyolysis
- Trauma
- Crush injury
- Seizures
- Prolonged immobilization
- Statin toxicity
- Snake bites
- Alcohol/drug intoxication
- Heat stroke
Risk of:
- Acute kidney injury (AKI) due to myoglobinuria
3. Trauma / Muscle Injury
- Burns
- Electric shock
- Vigorous exercise
- Surgery (particularly ortho/vascular)
4. Renal Failure
Myoglobin is cleared by the kidneys - impaired clearance → high serum levels.
5. Inflammatory Myopathies
- Polymyositis
- Dermatomyositis
- Muscular dystrophies
LOW Myoglobin
- Not clinically significant
- Seen rarely in muscle atrophy or chronic muscle wasting
Reference Intervals
(Tietz 8E + Mayo + ARUP + Cardiology guidelines)
Adults
- Males: 19 – 92 ng/mL
- Females: 12 – 76 ng/mL
(Equivalent: 19–92 µg/L, ~1.1–5.4 nmol/L)
Critical Levels
- > 100 ng/mL → Consider cardiac or skeletal injury
- > 300–500 ng/mL → Possible rhabdomyolysis
- > 5000 ng/mL → High risk of acute kidney injury
Diagnostic Uses
1. Early Rule-Out of Myocardial Infarction
- Very sensitive early
- Low specificity
- Used with troponin & CK-MB
2. Rhabdomyolysis Diagnosis
Myoglobin is one of the major markers along with:
- CK
- LDH
- Serum/urine myoglobin
- Potassium, phosphate (electrolyte abnormalities)
3. Acute Kidney Injury Risk Assessment
High serum myoglobin correlates with risk of:
- Pigment nephropathy
- AKI requiring dialysis
4. Trauma, Burns, Crush Injuries
Used to monitor muscle damage.
5. Drug & Toxin Monitoring
Elevated in:
- Alcohol intoxication
- Cocaine
- Statins
- Neuroleptics (NMS – neuroleptic malignant syndrome)
Analytical Notes
- Assay: immunoassay (chemiluminescent, ELISA)
- Interferences: hemolysis, lipemia
- Very short half-life (~2 hours)
- Renal impairment → falsely prolonged elevation
- Always interpret with troponin for cardiac evaluation
Clinical Pearls
- Normal myoglobin at 4 hours = MI very unlikely.
- Myoglobinuria → dark red/brown urine; dipstick positive for blood with no RBCs.
- Extremely high levels (>10,000 ng/mL) strongly predict acute kidney injury.
- Troponin has replaced myoglobin for diagnosis of MI, but myoglobin remains useful for early exclusion.
- Myoglobin rises faster than CK or troponin in trauma, seizures, and statin myopathy.
Interesting Fact
Myoglobin was the first protein whose 3D structure was solved (by John Kendrew, Nobel Prize 1962), making it a landmark molecule in modern biochemistry.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Muscle & Cardiac Markers
- AHA/ACC Guidelines - Cardiac Biomarkers
- Mayo Clinic Laboratories - Myoglobin
- ARUP Consult - Rhabdomyolysis & Cardiac Biomarkers
- Goldfrank’s Toxicologic Emergencies - Rhabdomyolysis
- MedlinePlus / NIH - Myoglobin Test