Myoglobin is a small protein found in heart & skeletal muscles that binds oxygen. It traps oxygen within muscle cells, allowing the cells to produce the energy required for muscles to contract. Diving mammals such as seals, whales are able to remain submerged for long periods because they have greater amounts of myoglobin in their muscles than other animals.
When heart or skeletal muscle is injured, myoglobin is released into the blood. So, myoglobin test is used to measure the level of myoglobin in your blood. Myoglobin increases in blood 2 to 3 hours after the first symptoms of muscle damage, including heart muscles. So, it’s considered as an early marker of myocardial infarction (MI). Serial sampling every 1-2 hours can increase the sensitivity & specificity; a rise of 25-40% over 1-2 hours is strongly suggestive of acute MI. Most important cardiac biomarkers are myoglobin, troponin & creatine kinase.
About 70% of iron is found in the red blood cells of your blood called hemoglobin & in muscle cells called myoglobin. Hemoglobin is essential for transferring oxygen in your blood from the lungs to the tissues. Myoglobin, in muscle cells, accepts, stores, transports & releases oxygen. Myoglobin helps muscles stay oxygenated by releasing stored oxygen into the muscle fibres. This also helps the muscles contract & relax. It also acts like an enzyme when it helps break down nitric acid & turn it into nitrate. By doing so, myoglobin helps the mitochondria inside cells, to have full access to oxygen for contractions.
Myoglobin may appear in urine when skeletal muscles have been damaged, in accidents or surgery. Drug use, alcohol use, seizures, prolonged vigorous exercise, & low phosphate levels can also damage skeletal muscles.
Normal range is upto 50 ng/mL. Rhabdomyolysis, severe muscle injury, malignant hyperthermia, muscle weakness, (dystrophy), myositis (disorder with inflammation in the skeletal muscle) also causes myoglobin increase in blood. High amounts of myoglobin in blood could even harm your kidneys, leading to kidney disease.
In severe/critical COVID-19 patients, myoglobin & troponin were predictors of mortality & the probability of conversion to critical illness, & myoglobin may be superior to troponin for predictive value.