Clinical Information

Myoglobin is a small 17.8 kDa oxygen-binding heme protein, present in striated muscle to carry and store oxygen in muscle cells. By virtue of its small size, myoglobin is readily filtered by the glomerulus and catabolized by endocytosis and proteolysis in the proximal tubule. Healthy subjects normally have low concentrations (less than 5%) of protein appearing in the urine. Injury to skeletal or cardiac muscle results in a large release of myoglobin into systemic circulation within a few hours, which can overwhelm tubular resorption causing notable quantities of myoglobin to appear in urine giving it a red-brown appearance. The presence of myoglobin in the urine is a risk factor for developing acute kidney injury. Myoglobin concentration declines rapidly, with a serum half-life of 2 to 3 hours and has been studied for its ability to predict acute kidney injury.

High concentrations appear very rapidly in the urine in various conditions, including some metabolic diseases.

Conditions that can lead to rhabdomyolysis associated with myoglobinuria include:

-Trauma or crush injury

-Heatstroke, hypothermia, malignant hyperthermia

-Seizures, strenuous exercise, prolonged immobility

-Hypoxic injury

-Metabolic disturbances in electrolyte concentrations

-Genetic disorders that lead to muscle cell breakdown

-Infections

-Drugs or toxins

The presence of myoglobin in the urine can indicate serious muscle injury, which is a risk factor for developing acute kidney injury. Rhabdomyolysis is often confirmed and monitored by measuring serum creatine kinase, electrolytes, kidney function, and urine tests for protein and blood. Myoglobin will give a positive reaction with hemoglobin test strips, though red blood cells will be absent upon microscopic review.