Test for Rhabdomyolysis

Rhabdomyolysis is a condition involving the breakdown and eventual necrosis (death) of skeletal muscle tissue. It most commonly occurs as a result of an injury, especially crush injuries, and those who abuse alcohol or take illicit drugs are at a higher risk. Symptoms of rhabdomyolysis are non-specific, so clinical testing is the best way to diagnose the condition. It is an acute condition, meaning it has a rapid onset and a short course, but it can result in severe and even life-threatening complications, so early diagnosis is the key to successful treatment.

CPK

• Creatine phosphokinase (CPK) is an enzyme that is found in skeletal tissue. As the muscles break down, they release creatine phosphokinase, resulting in an increase in CPK levels within 12 hours of the onset of rhabdomyolysis. These levels will remain high, peaking in about three days, then begin to drop between three and five days. In general, patients with rhabdomyolysis will have a peak CPK level about five times higher than normal, so a blood test specific for CPK level is a good indicator for the condition.

Myoglobin in Blood

• Myoglobin is a protein found in skeletal muscle as well as in the heart. When muscles are damaged, as in rhabdomyolysis, they release myoglobin into the blood. A blood test specific for myoglobin will be positive for those with rhabdomyolysis.

Blood Potassium Level

• One of the complications of rhabdomyolysis is hyperkalemia, which is an increased level of potassium. This occurs because as the muscle tissue breaks down, the cell membranes become leaky, allowing too much sodium in and too much potassium out. Therefore, a useful diagnostic test for rhabdomyolysis is a blood test looking at potassium levels, which will likely be very high compared with normal levels.

  Potassium is important in controlling muscle activity, including that of the heart. An increased level of potassium can result in cardiac arrhythmia or even cardiac arrest, so diagnosing the increased level is critical.

Urine Myoglobin

• One of the first clinical signs of rhabdomyolysis is tea-colored urine caused by the myoglobin released by the damaged muscle into the blood, which is then removed from the blood by the kidneys and excreted in the urine. This myoglobin can accumulate and cause an obstruction in the kidney tubes, which can lead to a life-threatening complication of kidney (renal) failure. A simple diagnostic test that may confirm the diagnosis of rhabdomyolysis is to test the urine for the presence of myoglobin using a dipstick. A positive result from this test, along with the results from the other diagnostic tests, can help to make a conclusive diagnosis.

Microscopic Urinalysis

• A microscopic urinalysis (observing a urine sample using a microscope) is another diagnostic test that can help to diagnose rhabdomyolysis. Performing a microscopic urinalysis can determine the presence of casts, which are tube-shaped particles that develop in the kidney tubules. Casts found in the urine can consist of various particles including fatty particles, red blood cells, white blood cells and kidney cells. Patients with rhabdomyolysis will have brown casts as well as uric acid crystals visible in the microscopic analysis.