A myoglobin blood test may be used to detect muscle damage. Myoglobin is a small, oxygen-binding protein found in heart and skeletal muscle. When heart or skeletal muscle is injured, myoglobin is released into the blood. Blood levels of myoglobin can rise very quickly with severe muscle damage and can be measured within a few hours following an injury.

Myoglobin is filtered from the blood by the kidneys and is released into the urine. Sometimes, a urine test is ordered to evaluate myoglobin levels in people who have had extensive damage to their skeletal muscles (rhabdomyolysis). Urine myoglobin levels reflect the degree of muscle injury and, since myoglobin is toxic to the kidneys, reflect the risk of kidney damage.

Sometimes, a myoglobin blood test may be used along with a troponin test as a cardiac biomarker to help detect a heart attack early.

The level of myoglobin in the blood starts to rise within 2-3 hours of a heart attack or other muscle injury, reaches its highest levels within 8-12 hours, and generally falls back to normal within one day. An increase in myoglobin is detectable sooner than troponin, but it is not as specific for heart damage and it will not stay elevated as long as troponin.

Although a negative myoglobin result effectively rules out a heart attack, a positive result must be confirmed by testing for troponin.

An increase in blood myoglobin means that there has been very recent injury to muscle tissue. Increased levels can occur, for example, in people who have had:

• Accidents that result in muscle trauma 

• Seizures

• Surgery

• Any muscle disease, such as muscular dystrophy

• Inflammation of skeletal muscles (myositis)

• Heart attack

Increased myoglobin levels can occur after muscle injections or strenuous exercise. Because the kidneys remove myoglobin from the blood, the myoglobin level may be high in people whose kidneys are failing. Heavy alcohol consumption and certain drugs can also cause muscle injury and increase myoglobin in the blood.

A urine dipstick test for hemoglobin can also be positive in the presence of myoglobin. If the urine dipstick test is positive and myoglobin is suspected to be the cause, it should be followed up with more specific testing for myoglobin.