What is kidney disease?
Kidney disease occurs when the kidneys are damaged and cannot function properly. Numerous conditions and diseases can result in damage to the kidneys, thus affecting their ability to filter waste from the blood while reabsorbing important substances. Generally, kidney disease may present or develop in a few different ways:
- Acute kidney injury (AKI) is the rapid loss of kidney function. It may be recognized when a person suddenly produces urine much less frequently and/or has a dramatic increase in the level of waste products in the blood that the kidneys normally filter out. AKI is often the result of trauma, illness, or a medication that damages the kidneys. It is most common in people who are already hospitalized, such as those who are critically ill and in the intensive care unit. If the damage caused by AKI persists, it can eventually progress to chronic kidney disease.
- Chronic kidney disease (CKD) occurs over time and is usually defined as lasting over 3 months. The most common causes are diabetes and high blood pressure (hypertension). According to the National Kidney Foundation, 26 million American adults have CKD and many more are at risk. However, in some cases, it is preventable or, if detected early enough, treatable to prevent or delay progression to kidney failure.
- Nephrotic syndrome is characterized by the loss of too much protein in the urine. It is caused by damage to the glomeruli and can be a primary disorder of the kidney or secondary to an illness or other condition, such as cancer or lupus. Along with a high amount of protein in the urine, signs and symptoms of nephrotic syndrome include a low amount of albumin in the blood, higher than normal lipid levels in the blood, and swelling (edema) in the legs, feet, and ankles. The condition may be acute or chronic, and the outcome can vary.
- Kidney failure, also called end-stage renal disease or ESRD, is the total or near total loss of kidney function and is permanent. Treatment with hemodialysis or kidney transplant is the only option at this stage of kidney disease to sustain life.
Various factors can cause different patterns of injury to the kidneys and can affect kidney function. Some factors affect the blood-filtering units, the nephrons, or parts of the nephrons, such as the glomeruli or the tubules. Some factors affect the passage of urine from the kidney while others cause damage to the kidney(s) as a whole.
The most common causes of and main risk factors for kidney disease are:
- Diabetes: a sustained high level of blood glucose from uncontrolled diabetes can over time damage the nephrons in the kidneys. This can be avoided by maintaining good glucose control.
- High blood pressure (hypertension): can damage blood vessels within the kidneys, preventing them from filtering wastes from the blood as they should. Hypertension can therefore cause CKD, but having CKD can cause high blood pressure as well.
- Family history of kidney disease: for example, polycystic kidney disease (PKD) is an inherited disorder in which cysts grow in the kidneys, reducing kidney function over time and eventually leading to kidney failure.
Some other examples of factors affecting the kidneys or patterns of kidney disease include:
- Glomerulonephritis (also called chronic nephritis or nephritic syndrome): a group of diseases that cause inflammation and damage to the blood filtering units of the kidneys (glomeruli) and the third most common type of kidney disease. As blood filtering becomes impaired, urine output decreases, water and waste products accumulate in the blood, and blood appears in the urine. Because the blood cells break down, urine often becomes brown instead of red. Certain body tissues swell with the excess water (a condition called edema). Outcomes can vary: the condition may go away in a few weeks, permanently reduce kidney function, or progress to end-stage renal disease.
- Obstruction: the urinary tract can become blocked, or obstructed, from such things as a kidney stone or tumor. The blockage can lead to infection and injury of the kidney.
- Autoimmune disease: sometimes an autoimmune disorder such as systemic lupus erythematosus or Goodpasture syndrome can lead to glomerular disease and affect the kidneys. In autoimmune diseases, the body's immune system mistakenly attacks and damages its own tissue and organs, including the kidneys.
- Infections: certain bacteria and viruses can infect the kidneys and cause damage. Repeated urinary tract infections (UTIs) that spread to the kidneys is an example.
- Immune response: infections in other parts of the body can stimulate an immune response that has an adverse effect on the kidneys. Examples include strep infection of the throat or skin, the skin infection impetigo, an infection inside the heart (endocarditis), or a viral infection such as HIV, hepatitis B, or hepatitis C.
- Congenital defects: defects present at birth, such as those that impede the normal flow of urine.
- Injury: trauma to the kidneys can cause AKI that can lead to chronic kidney disease.
- Toxins: some contrast dyes used for imaging procedures and certain medications can have toxic effects on the kidneys.
- Drugs: use and/or overuse of non-steroidal anti-inflammatory drugs (NSAIDS), such as over-the-counter ibuprofen, and various prescription drugs can damage the kidneys. Use of analgesics (pain killers) has been associated with two different forms of kidney damage: acute renal failure and a type of chronic kidney disease called analgesic nephropathy. Certain antibiotics can be directly toxic to the kidneys if their levels are too high. Other drugs may trigger an immune response by the body that subsequently causes kidney damage.
- Pre-renal azotemia: any situation in which there is severe blood loss or reduced blood flow may prevent the kidneys from working properly, such as a blood clot, severe burn, severe dehydration, or septic shock.
- Interstitial nephritis: a kidney disorder in which the spaces between the kidney tubules become inflamed and swollen. It may be acute or chronic. Causes include side effects of certain medications, certain autoimmune disorders, and having a low blood potassium level or a high blood level of calcium or uric acid. It is associated with decreased urine output, blood in the urine, and edema. Usually, this is a short-term condition.
- Acute tubular necrosis (ATN): a kidney disorder involving damage to the tubules in the kidneys. It is one of the most common causes of kidney failure in hospitalized patients. It is caused by a lack of oxygen to the kidney tissues or from damage to the kidneys by toxic substances such as contrast dyes used for x-ray studies and certain medications. In most cases, ATN is reversible.