Azotemia is a build up of nitrogen waste products in the blood.
It is usually the result of problems in the kidney that prevent it from filtering the blood correctly.
The kidneys and the renal system usually filter waste products out of the blood. They also make urine to help eliminate those wastes, along with extra water, from the body.
If the kidneys are damaged or not working properly, they are not able to remove the waste products from the blood.
There are three types of azotemia:
- Prerenal azotemia: Prerenal azotemia occurs when something that is affecting the blood circulation affects how well the kidneys function. When blood pressure to the kidney is low, the kidney is not able to properly filter out waste products or make urine.
- Intrarenal azotemia: Intrarenal azotemia, also known as acute renal failure (ARF) or acute kidney injury (AKI), is attributed to problems with the kidney itself.
- Postrenal azotemia: Postrenal azotemia occurs when there is a blockage in the urinary system after the urine has left the kidney.
Some people with azotemia experience no symptoms. Others may have symptoms of dehydration, which can include:
The cause of azotemia depends on the type.
Prerenal azotemia is most common in people who are in the hospital for a different condition. Any condition that causes reduced blood flow to the kidney can cause this condition.
Conditions may include:
- long-term vomiting or diarrhea
- heat exposure
- heart failure
- blockage of the artery that supplies the kidney with blood
There are many different causes of intrarenal azotemia. They include:
- Medications and drugs: Nephrotoxins may damage the kidneys. Common nephrotoxins include cocaine, cyclosporine, certain antibiotics, angiotensin-converting enzyme (ACE) inhibitors, and nonsteroidal anti-inflammatory drugs (NSAIDs).
- Infection: Kidney infections can damage the tubules within the kidney that filter the blood.
- Vascular disease: Damage to the small blood vessels in the kidney can cause blockages and damage to the tissues. Blood clots in the kidney or narrowing of the arteries are the most common vascular causes of intrarenal azotemia.
Postrenal azotemia occurs when there is a blockage in the tubes that leave the kidney. Common causes of these blockages include:
- urinary catheter
- urinary crystals
- enlarged prostate
Additional risk factors
There are several risk factors for developing azotemia, including:
- diabetes mellitus
- renal insufficiency
- heart failure
- advanced age
- taking a nephrotoxic drug
Before doing any diagnostic testing, a doctor will take a thorough medical history, including recent medications, infections, and other symptoms. Next, the doctor will perform a physical exam to look for potential causes or medical problems.
Diagnosing azotemia is usually done with a simple blood or urine test. The doctor will test the blood for markers of kidney function, including blood creatinine and blood urea nitrogen (BUN).
These are both substances that the kidney filters out. If there are high levels of either or both of these substances in the blood, it indicates that the kidneys are not working well.
Urine tests for osmolality, specific gravity, sodium, and creatinine can also provide information about how hydrated a person is, which is another indication of kidney function.
Sometimes, a doctor will order an ultrasound or additional tests, depending on the results of the physical exam and any blood or urine testing already performed.
Many factors go into determining a treatment plan for a person with azotemia.
If a doctor has identified the cause, it is important to address it first. For example:
- Someone with postrenal azotemia that is due to a tumor needs to have the tumor removed and receive treatment for kidney function.
- Someone who is taking a nephrotoxic drug may need to switch to an alternative medication that does not affect the kidneys.
- Surgery may be required to relieve an obstruction that is causing urine to back up into the renal system.
People with intrarenal azotemia are also at higher risk for developing electrolyte or fluid imbalances. Treatment for this may include taking oral or intravenous (IV) medications.
In most cases, this means that hospitalization is necessary until kidney function and electrolyte imbalances are corrected and stabilized. Intravenous fluids can also be used to increase the blood volume.
Medications are often used to help the heart pump more efficiently or raise the blood pressure. This course of treatment helps to improve blood flow and pressure through the kidney.
In some cases, a person with intrarenal azotemia may need kidney dialysis. Dialysis is a procedure where the blood is removed from the body through an intravenous (IV) line, filtered in a dialysis machine, and then replaced back into the body through a second line.
Kidney dialysis must be performed 3 to 4 times per week and requires several hours for each session.
In addition to treating the cause, it is important for doctors to try to prevent renal failure from occurring whenever possible.
A person who has risk factors for azotemia should not be prescribed a nephrotoxic drug and should avoid diagnostic testing that requires the use of contrast dye.
Postrenal azotemia is easily treated and can even be reversed once the cause has been identified and addressed.
Prerenal azotemia can also be reversed if the cause is identified and treated very early within the disease process. If not, serious damage to the kidneys can occur.
Intrarenal azotemia is a serious condition that can be fatal if not treated. The outlook depends on several factors, including the severity of the damage and underlying cause.
For example, an otherwise healthy person with ARF may have a better outlook than a hospitalized patient with multiple medical problems.
It is important for anyone with risk factors or symptoms of azotemia to be under the care of a doctor. Following the prescribed treatment plan is essential to prevent more severe kidney damage or loss of life.