Azotemia is a condition of the blood characterized by elevated levels of nitrogen-containing compounds. Among the compounds that are at abnormally high levels in azotemia are urea, creatinine, and various waste products of bodily processes.

Causes And Indications

Azotemia is a sign of kidney dysfunction, in that it is usually the result of inadequate blood filtering by the kidneys. As a key result of kidney disease, the condition is useful in diagnosis and also represents the primary danger inherent in kidney disorders and renal failure. As noted below, azotemia can result from various causes and although it always shows a failure of the kidneys and ureters to process and eliminate wastes properly, it is not always a sign of kidney disease.

Diagnosis And Symptoms

The primary test for azotemia is a blood chemistry analysis for the prevalence of nitrogen-containing compounds in the blood. There are three main types of azotemia: prerenal azotemia, primary renal azotemia, and postrenal azotemia. None of these types of azotemia typically produces severe overt symptoms; however that’s largely due to semantics, as when azotemia progresses to the point where major overt  symptoms appear it’s usually called “uremia” instead. It’s the same condition, just worse. Uremia is a sign that the problems with the kidneys have become very serious indeed and something had better be treated quickly.

All three types of azotemia are characterized by a decrease in the blood filtration rate of the kidneys, but they are caused by different things. A BUN-to-creatinine ratio blood test can help to distinguish one type of azotemia from another.

Types

Prerenal azotemia is caused by a reduced blood flow from the kidneys. This can result from various causes, including blood loss, shock, trauma, congestive heart failure, and blockage of the renal artery. Prerenal azotemia is not a sign of kidney disease as such.

Prerenal azotemia results in a BUN-to-creatinine ratio above 20. It’s a fairly common condition among people who are hospitalized and undergoing surgery or in emergency rooms for trauma.

Primary renal azotemia or renal azotemia is associated with renal failure. It often progresses to uremia, which is basically a more severe form of azotemia –– thus, this is another way of saying that when azotemia is due to acute renal failure, it’s likely to get worse. Primary renal  azotemia is characterized by a BUN:creatinine ratio of less than 15.

Postrenal azotemia is caused by a blockage of urine flow below the kidneys. This has various causes, the most common of which are probably kidney stones and pregnancy; however, the ureters can be compressed by cancer, prostatic hyperplasia, or bladder stones, and there are various congenital conditions that can also cause it. In postrenal azotemia the BUN:creatinine ratio is above 15 but less than 20.

Although azotemia is usually free of overt symptoms, it can result in decreased urine flow, fatigue, thirst, rapid pulse, dry mouth, and occasionally swelling and uremic frost.

Prevention And Treatment

Prevention and treatment of azotemia depends on the type of azotemia and the underlying cause. Very different treatments will be called for in the case of blood loss than kidney stones or acute renal failure, obviously. For prerenal azotemia, the goal is to restore blood flow to the kidneys before serious damage occurs. That can mean intravenous restoration of blood fluids and of course treatment of the injuries causing the problem. The possibility of azotemia as a complication of trauma is always important to consider in treating injuries.

Symptomatic treatment of azotemia itself can take the form of rehydration, maintenance of blood chemistry balance, or in severe cases dialysis to replace kidney function (normally the last is only prescribed in cases of acute renal failure). Acute renal failure is treated by hospitalization and intensive care. It’s a rapid-onset disease and is potentially fatal, but is not to be confused with chronic kidney disease even though the late stages of the latter can produce similar levels of kidney failure. Acute renal failure is often reversible. It can result from the same things that cause prerenal azotemia (such as trauma and loss of blood flow to the kidneys), and also from trauma to the kidneys themselves and from various bacterial and viral infections (including step throat). Hospital care, dialysis, pain management, and symptomatic treatment allows the kidneys to repair themselves and restore kidney function in cases of acute renal failure most of the time.

When azotemia results from chronic kidney disease, damage to the kidneys may be permanent and, in the late stage of the disease, the only permanent treatment is a kidney transplant. Dialysis can be used to replace kidney function on an ongoing basis.

Prevention of azotemia is a matter of taking care of kidney function through diet, weight management, exercise, and early detection of  problems.