What is Myoglobinuria?
Myoglobin is a protein with iron content found mainly in the sarcoplasm of skeletal and heart muscles. It has a part known as heme that helps it serve as a transporter and storage for oxygen in muscle cells in our body. Interestingly, Myoglobin can hold oxygen better than hemoglobin, which is the protein in red blood cells that carries oxygen. As a result, myoglobin can receive oxygen from hemoglobin, thus carrying it from the blood to the muscle tissues.
The condition called ‘myoglobinuria’ is when there’s an unusually high amount of myoglobin in the urine. Since myoglobin is in the muscle cells, myoglobinuria is almost always due to damage to the cell coverings of myocytes, which are muscle cells. The breakdown of these muscle cells is also called rhabdomyolysis, which results in myoglobin being released into the blood. Eventually, it’s filtered by the glomerulus, a part of the kidney’s filtration system, and ends up in the renal tubule, which forms part of the urine.
In the following article, we’ll be exploring the causes, how myoglobinuria occurs in the body, its evaluation, treatment, and potential complications.
What Causes Myoglobinuria?
Myoglobinuria is a condition which arises when myoglobin, a protein found in muscle cells, is released into the urine. This typically happens when the cell walls of muscle cells are damaged. There are many possible reasons why these muscle cells might get damaged, which can be grouped into physical and non-physical causes.
Physical causes involve direct harm to the body. Some examples are trauma, severe pressure from crushing, excessive heat or cold, severe heat-induced illness, large-scale burns, seizures, intense exercise, and being immobile for a long time.
Contrarily, non-physical causes don’t involve direct bodily harm. They include a lack of oxygen to the muscle cells, changes in the body’s normal levels of substances (like potassium, phosphate, sodium, calcium), genetic disorders, infections, and certain drugs and toxins.
For instance, lack of oxygen harm could be due to carbon monoxide poisoning, blood clots in the vessels, or inflammation of the vessels. Some examples of genetic disorders that can lead to muscle cell breakdown include disorders of carbohydrate and fat metabolism, muscular dystrophy, and specific muscle inflammation disorders.
Certain infections like those from viruses including coxsackievirus, malaria, herpes virus, influenza virus, HIV, along with bacteria like Legionella and salmonella can also cause this condition. Specific drugs and toxins such as alcohol, sleeping pills, cocaine, methadone, cholesterol-lowering drugs, and others, can lead to myoglobinuria as well.
Risk Factors and Frequency for Myoglobinuria
Myoglobinuria, which is directly connected to muscle damage, is tricky to determine its exact rate of occurrence. Nonetheless, it is mostly found in younger individuals largely due to a higher risk of infections and injuries. Athletes, for example, are more susceptible to such injuries, leading to a condition called rhabdomyolysis, which in turn triggers a higher incidence of myoglobinuria among them. Young people also tend to encounter more infections that lead to muscle inflammation, known as myositis, causing more cases of myoglobinuria among this group.
Additionally, situations like natural disasters, earthquakes, in particular, are infamous for causing widespread injuries such as rhabdomyolysis and crush syndromes. As a result, regions affected by these disasters often see a rise in instances of myoglobinuria.
Signs and Symptoms of Myoglobinuria
Myoglobinuria is a medical condition that is often a sign of a more serious problem called rhabdomyolysis. The most common symptoms are muscle weakness, muscle pain, and dark urine. However, it’s possible for someone to only have dark urine and no other symptoms. Some people might also experience general feelings of being tired or having body aches along with dark urine.
When doctors are trying to figure out what’s causing someone’s myoglobinuria, they’ll usually ask about things that could have led to the onset of rhabdomyolysis. This could include a history of physical trauma, using certain drugs, engaging in intense exercise, being in a coma, or having a muscle tissue disorder.
Physicians will also carry out a physical exam. They might find signs of muscle weakness, tenderness, or evidence of trauma. However, if the condition isn’t caused by trauma, the physical exam might not show any abnormalities. If there is muscle tenderness, it’s usually more noticeable in the muscles closer to the center of the body when the cause is inflammation.
Testing for Myoglobinuria
If your pee looks dark, it’s usually a sign that your doctor should run some tests. First, they’ll typically check a sample of your urine with a tool called a urine dipstick. If the test is positive for heme (a component of red blood cells), the next step is to look at the urine under a microscope. If there are no red blood cells found, it suggests that myoglobin is present in the urine. Now, you might wonder what is myoglobin? It’s a protein found in your muscles.
There are more exact measures available to check the levels of myoglobin in your urine, like immunohistochemistry, spectrophotometry, and radioimmunoassay tests. However, they’re not typically needed for standard care. Your doctor may also check the levels of creatine kinase, an enzyme found in the heart and muscles, in your blood. If these levels are high, it helps to confirm that muscle injury is causing the myoglobin to appear in your urine.
Your doctor might also ask for tests that look at the levels of different electrolytes in your blood or how well your kidneys are functioning. These tests are important because they can show if there’s a high amount of potassium in your blood (hyperkalemia) or any damage to your kidneys (acute kidney injury) – both of these can be side effects of the presence of myoglobin in your urine.
They also might want to check if you’re taking any medication that could cause rhabdomyolysis, a condition that occurs when a large amount of muscle tissue breaks down, releasing myoglobin into the bloodstream.
Lastly, they may conduct a few more tests to identify the actual cause of rhabdomyolysis. This could involve a urine test to check for drugs or alcohol or a blood test that checks your erythrocyte sedimentation rate (ESR), which is a way of measuring inflammation in the body. Inflammatory diseases like dermatomyositis and polymyositis are known to cause rhabdomyolysis.
Treatment Options for Myoglobinuria
The key aim of treating myoglobinuria, a condition where muscle protein is found in urine, is to prevent damage to the kidneys. The initial treatment mainly involves rehydration, which helps the kidneys to remove the myoglobin more easily. This is achieved by giving the patient fluids like normal saline or Ringer’s lactate. The amount of these fluids is adjusted according to the patient’s needs to make sure they are producing 200 to 300 mL of urine per hour.
Imbalances in the patient’s level of electrolytes like potassium are carefully addressed as part of the treatment.
Since acidic urine can lead to the formation of certain types of solid substances, some experts recommend making the urine more alkaline using sodium bicarbonate. The theory is that this might help to prevent the formation of these solids and stop uric acid from crystallizing.
The use of diuretics, drugs that increase urine production, is a point of debate in these cases. The evidence does not strongly support their use. However, medications such as mannitol and furosemide may be used in certain patients to help prevent a specific type of kidney failure where urine production doesn’t reduce significantly.
If rehydration doesn’t help, the last option is often hemodialysis. This is a procedure that functionally replaces the kidneys by eliminating harmful substances from the bloodstream and correcting imbalances in electrolytes. There is some evidence that starting hemodialysis early in patients with rhabdomyolysis, a condition where muscle tissue breaks down and releases substances into the blood, may improve kidney outcomes.
What else can Myoglobinuria be?
There are several reasons why someone’s urine might be dark red or almost black. This is a condition known as pigmenturia. It’s important to distinguish pigmenturia from another condition, called myoglobinuria.
Other things that can cause pigmenturia include:
- Acute intermittent porphyria
- Blood present in the urine (hematuria)
- Hemoglobin present in the urine (hemoglobinuria)
- Bilirubin present in the urine (bilirubinuria)
- Condition called alkaptonuria
- Consumption of beets (beeturia)
What to expect with Myoglobinuria
In general, the outlook for myoglobinuria, a condition where there’s excessive amounts of a protein called myoglobin in the urine, is good. Although it has the potential to lead to acute kidney injury (AKI), a short-term kidney damage or failure, most of the time, such damage to the kidneys is minimal and can be reversed.
Possible Complications When Diagnosed with Myoglobinuria
Acute kidney injury (AKI) is often associated with myoglobinuria and is known to be its most common complication. It’s been found in research that around half of rhabdomyolysis cases could possibly cause AKI. Interestingly, about 10 percent of AKI cases are due to rhabdomyolysis.
Another significant complication is disturbance in the body’s electrolyte balance, mainly hyperkalemia. When muscle cells get damaged, they spill their inner contents, causing this problem.
Most Common Complications:
- Acute kidney injury (AKI)
- Electrolyte disturbance, particularly hyperkalemia
Preventing Myoglobinuria
After receiving the right treatment, it’s crucial for patients to learn about what causes myoglobinuria, a condition where a protein called myoglobin is released into the urine due to muscle damage. They need to understand how to prevent this from happening again based on their unique health situations.
Patients must know that myoglobinuria can reoccur. They should be aware that symptoms like dark-colored urine or muscle pain may hint towards this condition. In such cases, they should seek medical attention promptly. Doctors can quickly detect myoglobinuria through a simple urine test.
Some people may experience myoglobinuria because of certain prescribed medications. In these cases, patients should learn about how their medicine may be contributing to the problem, and if possible, the doctor may switch to another medication.
If overdoing physical activities has resulted in myoglobinuria, patients should be guided on adjusting their exercise routines and levels of intensity. Staying well-hydrated during these activities is also crucial.
For those who have developed myoglobinuria due to recreational drug use or excessive alcohol consumption, they should receive thorough counseling. Full information about rehabilitation centers should be provided if they wish to stop using such substances. Contact details of these centers should also be made readily available.
