Myoglobin (MB) Lab Values

Hey everyone. Abby with nursing.com. In this lesson, we’re going to talk about myoglobin. We’ll talk about why we draw this lab, its normal values, and times when we might see it increased or decreased. Are you ready? Let’s get started! 

Myoglobin, abbreviated MB, measures in the blood to detect muscle damage or injury. Myoglobin is interesting. Doesn’t it sound a lot like hemoglobin? Well, they have some really similar properties. It’s an oxygen binding protein and it’s found in striated muscle like this, that you can see here. It enters the bloodstream only as a result of muscle damage. It’s measured by the blood or the urine to evaluate for that muscle damage. However, it’s non-specific to the location of injury. There are other lab values that are more specific. 

Some clinical indications for why we might draw this mild globe lab value, are in times of trauma. Also, if there are disorders or conditions that deal with muscularity like muscular dystrophy. Also, in times of really scary, bad muscle damage like rhabdomyolysis. It can also be indicated for kidney failure. If we start to see the myoglobin in the urine, we get that kind of coffee or tea-colored urine. And formerly, it was used a lot in the diagnosis or detection of STEMI, or myocardial infarction. It’s no longer standard practice, it’s far more reliable as a lab when used for skeletal muscle damage. 

Normal therapeutic values are between 25 and 72 nanograms per deciliter. It can be obtained either in a plain red tube or a serum separator tube like you can see here. When lab values are increased, that of course means we’ve got some muscular damage. So, the myoglobin is actually leaking out of the muscle and into the bloodstream. Now, it could be from trauma, excessive physical activity, to the point where someone gets injured, or in burns. We talked a little bit about rhabdo, that’s really scary muscle lysis, right? And so, of course the myoglobin is going to leak out into the vasculature. It can also be seen in seizures, post-surgery, and in conditions or diseases like muscular dystrophy, or inflammatory states like myositis. And then, another time that we see it, and when it’s particularly valuable, is to evaluate for muscle ischemia, like compartment syndrome, or if there are blood clots that lead to ischemia in the muscle. Low myoglobin when it’s measured, doesn’t really have a very significant indication of disease or disorder. What it means when the myoglobin is low in the bloodstream, is that the myoglobin is exactly where it belongs, in the muscles binding oxygen and providing more oxygen for these muscles that are doing so much work. 

Linchpins for this lesson are that myoglobin is a protein that binds oxygen in striated muscle, and it’s measured in the event of muscle damage, or to evaluate for ischemia. Normal values are between 25 and 72 nanograms per deciliter. We’ll see values increased when there’s muscle damage and when it’s decreased, there’s likely no clinical significance. Remember that myoglobin is in the muscle exactly where it belongs, providing oxygen to the tissue. 

This wraps up our lesson on myoglobin. You all did great. Remember, we love you guys, now go out, be your best self today and as always, happy nursing.

References:

• https://my.clevelandclinic.org/health/diagnostics/22142-myoglobin#:~:text=Myoglobin%20Test,location%20of%20the%20muscle%20damage.
• https://www.ucsfhealth.org/medical-tests/myoglobin-blood-test
• https://pathologytestsexplained.org.au/learning/test-index/myoglobin
• https://www.uptodate.com/contents/biomarkers-of-myocardial-injury-other-than-troponin?search=myoglobin%20lab&sectionRank=1&usage_type=default&anchor=H2&source=machineLearning&selectedTitle=1~111&display_rank=1#H2
• https://www.uptodate.com/contents/laboratory-test-reference-ranges-in-adults?search=myoglobin%20lab&sectionRank=1&usage_type=default&anchor=H4206420720&source=machineLearning&selectedTitle=4~111&display_rank=4#H4206420720