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Why Is My Dog's Free Blood Myoglobin Level Increased?

Why Is My Cat's Free Blood Myoglobin Level Increased?

To see what normal blood and urine values are for your pet, go here

For an explanation of causes of most abnormal blood and urine tests go here

To see how tests are often grouped, go here

Ron Hines DVM PhD

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Myoglobin In The Blood (myoglobinemia)

Myoglobin In The Urine (myoglobinuria)

Myoglobin belongs in your pet's muscle cells - not free in its blood stream or urine.

Your dog or cat stores oxygen in two slightly different molecules. One is the hemoglobin that makes up ~94% of the dry weight of your pets red blood cells. Hemoglobin's job is to transport oxygen throughout its body.

The other is myoglobin, a smaller but similar molecule that stores oxygen within its muscle and heart cells. Both contain heme and the heme enzymes (heme-dependent peroxidases,"peroxidase-like" activity) that give a positive reaction on the blood detection square on standard urine dipsticks that your veterinarian uses to detect blood in your pet’s urine.  In those tests, the reaction of one is the same as the reaction of the other.

So on rare occasions, a blood or hemoglobin "positive” urine sample is actually a myoglobin positive sample.

When hemoglobin is detected in your pet’s urine (hematuria), it is usually due to red blood cells leaking into the urine. But it can also be due to spill-over of free hemoglobin circulating in your pet’s blood after some event that destroyed red blood cells while they were in the circulation (hemolytic anemia).

When the positive reaction is actually detecting myoglobin (myoglobinuria), it is because muscle cells have been injured somewhere in your pet’s body.

Urine that contains myoglobin is often visibly dark or brownish. On microscopic exam, there will be no red blood cells present (other than in the very unlikely situation of having two health issues occurring simultaneously).

Your veterinarian is unlikely to attempt any tests that distinguish between myoglobin and hemoglobin (immunoassays exist but are rarely used).

What the vet will do is size up the pet’s history. Was the animal hit by a car ? Did it experienced other trauma ? Was it under extreme exertion ? Are muscles painful, stiff and swollen? If so, the vet will look at your dog or cat ‘s CK (and probably AST) levels. If both of them are high, muscle injury and myoglobin probably account for the positive urine results.

Muscle damage and free myoglobin in the blood or urine is a rare event. (myoglobinemia/myoglobinuria). It is seen most frequently in working greyhounds – because of their lifestyle. When it occurs, the condition is called rhabdomyolysis.

Theoretically, any severe muscle trauma, crushing, struggling, exertion or  prolonged restraint to any pet could cause rhabdomyolysis. I have not run into it in dogs or cats. I do see it frequently in wildlife where it is called “capture myopathy”. In those animals, it often result in kidney failure. 
Complementary tests :

CBC/WBC and blood chemistry panel, with particular attention to CK and ALT levels , muscle biopsy

.................... DxMe