What are the kidneys and what do they do?
The two kidneys are bean-shaped organs located just below the rib cage, one on each side of the spine. Every day, the two kidneys filter about 120 to 150 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra fluid.
Blood enters the kidneys through arteries that branch inside the kidneys into tiny clusters of looping blood vessels. Each cluster is called a glomerulus, which comes from the Greek word meaning filter. The plural form of the word is glomeruli. There are approximately 1 million glomeruli, or filters, in each kidney. The glomerulus is attached to the opening of a small fluid-collecting tube called a tubule. Blood is filtered in the glomerulus, and extra fluid and wastes pass into the tubule and become urine. Eventually, the urine drains from the kidneys into the bladder through larger tubes called ureters.
How do glomerular diseases interfere with kidney function?
Glomerular diseases damage the glomeruli, letting protein and sometimes red blood cells leak into the urine. Sometimes a glomerular disease also interferes with the clearance of waste products by the kidney, so they begin to build up in the blood. Furthermore, loss of blood proteins like albumin in the urine can result in a fall in their level in the bloodstream. In normal blood, albumin acts like a sponge, drawing extra fluid from the body into the bloodstream, where it remains until the kidneys remove it. But when albumin leaks into the urine, the blood loses its capacity to absorb extra fluid from the body. Fluid can accumulate outside the circulatory system in the face, hands, feet, or ankles and cause swelling.
How is glomerular disease diagnosed?
Patients with glomerular disease have significant amounts of protein in the urine, which may be referred to as “nephrotic range” if levels are very high. Red blood cells in the urine are a frequent finding as well, particularly in some forms of glomerular disease. Urinalysis provides information about kidney damage by indicating levels of protein and red blood cells in the urine. Blood tests measure the levels of waste products such as creatinine and urea nitrogen to determine whether the filtering capacity of the kidneys is impaired. If these lab tests indicate kidney damage, the doctor may recommend ultrasound or an x-ray to see whether the shape or size of the kidneys is abnormal. These tests are called renal imaging. But since glomerular disease causes problems at the cellular level, the doctor will probably also recommend a kidney biopsy—a procedure in which a needle is used to extract small pieces of tissue for examination with different types of microscopes, each of which shows a different aspect of the tissue. A biopsy may be helpful in confirming glomerular disease and identifying the cause.
What causes glomerular disease?
A number of different diseases can result in glomerular disease. It may be the direct result of an infection or a drug toxic to the kidneys, or it may result from a disease that affects the entire body, like diabetes or lupus. Many different kinds of diseases can cause swelling or scarring of the nephron or glomerulus. Sometimes glomerular disease is idiopathic, meaning that it occurs without an apparent associated disease.
The categories presented below can overlap: that is, a disease might belong to two or more of the categories. For example, diabetic nephropathy is a form of glomerular disease that can be placed in two categories: systemic diseases, since diabetes itself is a systemic disease, and sclerotic diseases, because the specific damage done to the kidneys is associated with scarring.
Autoimmune Diseases
When the body’s immune system functions properly, it creates protein-like substances called antibodies and immunoglobulins to protect the body against invading organisms. In an autoimmune disease, the immune system creates autoantibodies, which are antibodies or immunoglobulins that attack the body itself. Autoimmune diseases may be systemic and affect many parts of the body, or they may affect only specific organs or regions.
Hereditary Nephritis—Alport Syndrome
The primary indicator of Alport syndrome is a family history of chronic glomerular disease, although it may also involve hearing or vision impairment. This syndrome affects both men and women, but men are more likely to experience chronic kidney disease and sensory loss. Men with Alport syndrome usually first show evidence of renal insufficiency while in their twenties and reach total kidney failure by age 40. Women rarely have significant renal impairment, and hearing loss may be so slight that it can be detected only through testing with special equipment. Usually men can pass the disease only to their daughters. Women can transmit the disease to either their sons or their daughters. Treatment focuses on controlling blood pressure to maintain kidney function.
Sclerotic Diseases
Glomerulosclerosis is scarring (sclerosis) of the glomeruli. In several sclerotic conditions, a systemic disease like lupus or diabetes is responsible. Glomerulosclerosis is caused by the activation of glomerular cells to produce scar material. This may be stimulated by molecules called growth factors, which may be made by glomerular cells themselves or may be brought to the glomerulus by the circulating blood that enters the glomerular filter.
Diabetic nephropathy is the leading cause of glomerular disease and of total kidney failure in the United States. Kidney disease is one of several problems caused by elevated levels of blood glucose, the central feature of diabetes. In addition to scarring the kidney, elevated glucose levels appear to increase the speed of blood flow into the kidney, putting a strain on the filtering glomeruli and raising blood pressure.
Chronic Kidney Disease
Most forms of glomerular disease develop gradually, often causing no symptoms for many years. Chronic kidney disease (CKD) is the slow, gradual loss of kidney function. Some forms of CKD can be controlled or slowed down. For example, diabetic nephropathy can be delayed by tightly controlling blood glucose levels and using ACE inhibitors and ARBs to reduce proteinuria and control blood pressure. But CKD cannot be cured. Partial loss of renal function means that some portion of the patient’s nephrons have been scarred, and scarred nephrons cannot be repaired. In many cases, CKD leads to kidney failure.
What are kidney failure and end-stage renal disease?
Kidney failure is the acute or chronic loss of 85 percent or more kidney function. End-stage renal disease (ESRD), is kidney failure that is treated by dialysis or kidney transplant. Depending on the form of glomerular disease, kidney function may be lost in a matter of days or weeks or may deteriorate slowly and gradually over the course of decades.
Acute Renal Failure
A few forms of glomerular disease cause very rapid deterioration of kidney function. For example, PSGN can cause severe symptoms (hematuria, proteinuria, edema) within 2 to 3 weeks after a sore throat or skin infection develops. The patient may temporarily require dialysis to replace renal function. This rapid loss of kidney function is called acute renal failure (ARF). Although ARF can be life-threatening while it lasts, kidney function usually returns after the cause of the kidney failure has been treated. In many patients, ARF is not associated with any permanent damage. However, some patients may recover from ARF and subsequently develop CKD.
Kidney Failure
To stay alive, a patient with kidney failure must go on dialysis—hemodialysis or peritoneal dialysis—or receive a new kidney through transplantation. Patients with CKD who are approaching kidney failure should learn as much about their treatment options as possible so they can make an informed decision when the time comes. With the help of dialysis or transplantation, many people continue to lead full, productive lives with kidney failure.