Myoglobin may be ordered as a cardiac biomarker, along with troponin, to help diagnose or rule out a heart attack. Levels of myoglobin start to rise within 2-3 hours of a heart attack or other muscle injury, reach their highest levels within 8-12 hours, and generally fall 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.
Sometimes, a urine test is ordered to evaluate myoglobin concentrations in those who have had extensive damage to their skeletal muscles (rhabdomyolysis). Blood levels of myoglobin can rise very quickly with severe muscle injury. Urine myoglobin concentrations reflect the degree of muscle injury and, since myoglobin is toxic to the kidneys, reflect the risk of kidney damage.
Myoglobin is not widely used for diagnosing heart attacks because it has largely been replaced by troponin, which is much more specific. If the myoglobin test is available, it may be ordered to assess persons with chest pain who are suspected of having a heart attack. Blood samples are drawn on admission and every 2-3 hours for up to 12 hours in those who come to the emergency room with a possible heart attack.
Urine myoglobin may be ordered when there has been extensive injury to skeletal muscle, resulting in the rapid breakdown of muscle, and damage to the kidneys is suspected.
An increase in blood myoglobin means that there has been very recent injury to the heart or skeletal muscle tissue. Additional tests, such as troponin, are necessary to determine where the damage has occurred. Because myoglobin is also found in skeletal muscles, increased levels can occur in people who have accidents, seizures, surgery, or any muscle disease, such as muscular dystrophy.
If myoglobin does not increase within 12 hours following the onset of chest pain, a heart attack is very unlikely.
Myoglobin levels are normally very low or not detectable in the urine. High levels of urine myoglobin indicate an increased risk for kidney damage and failure. Additional tests, such as BUN, creatinine, and urinalysis, are done to monitor kidney function in these patients.
Increased myoglobin levels can occur after muscle injections or strenuous exercise. Because the kidneys remove myoglobin from the blood, myoglobin levels may be high in people whose kidneys are failing. Heavy alcohol consumption and certain drugs can also cause muscle injury and increase myoglobin in 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.
This article was last reviewed on November 16, 2011. | This article was last modified on January 30, 2012.
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