Myoglobin

Myoglobin is used infrequently as a cardiac biomarker. Its historic use was as an early-onset marker since it becomes elevated first, before CK-MB and troponin. For this reason, it once was used to help rule out AMI. Troponin has now replaced myoglobin for this indication.

Myoglobin is an oxygen-binding protein in cardiac and skeletal muscle. It is released after muscle injury earlier than cardiac troponins and CK-MB and returns to normal faster than either of these other markers. It rises within 2 – 4 hours after chest pain, peaks in 6 – 12 hours, and is usually normal within 24 – 36 hours.

Myoglobin is present in all muscles, not just cardiac muscle. It is actually the reason muscle is red in color. Thus, it is a very nonspecific marker for cardiac damage. It can be elevated after exercise and in many other clinical scenarios. For these reasons, myoglobin is rarely measured. Many laboratories no longer offer myoglobin testing and emergency room physicians are no longer trained in its use. As troponin assays have become more sensitive, they have replaced myoglobin assays.

Myoglobin reference ranges for adults when an immunoassay method is used are seen in Table 4.