All of the following are TRUE regarding myoglobinuria, EXCEPT:
Correct Answer: The serum is deep red in color
Description: The red pigment myoglobin, responsible for much of the color of muscle, is an iron-protein compound present in the sarcoplasm of striated skeletal and cardiac fibers. Destruction of striated muscle, regardless of the cause liberates myoglobin, and because of its relatively small size, the molecule filters through the glomeruli and appears in the urine, impaing to it a burgundy-red color. Because of the low renal threshold for myoglobin, excretion of the pigment is so rapid that the serum remains uncolored. It is estimated that 200 g of muscle must be destroyed to color the urine visibly. As with hemoglobinuria, the guaiac and benzidine tests performed on urine are positive if myoglobin is present. Myoglobinuria should thus be suspected when the urine is deep red and the serum is normal in color. Ref: Ropper A.H., Samuels M.A. (2009). Chapter 45. Electrophysiologic and Laboratory Aids in the Diagnosis of Neuromuscular Disease. In A.H. Ropper, M.A. Samuels (Eds), Adams and Victor's Principles of Neurology, 9e.
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