The kidneys are a pair of organs located in the back of the abdomen. Each kidney is about 4 or 5 inches long -- about the size of a fist.
The kidneys' function are to filter the blood. All the blood in our bodies passes through the kidneys several times a day. The kidneys remove wastes, control the body's fluid balance, and regulate the balance of electrolytes. As the kidneys filter blood, they create urine, which collects in the kidneys' pelvis -- funnel-shaped structures that drain down tubes called ureters to the bladder.
Each kidney contains around a million units called nephrons, each of which is a microscopic filter for blood. It's possible to lose as much as 90% of kidney function without experiencing any symptoms or problems.
- Pyelonephritis (infection of kidney pelvis): Bacteria may infect the kidney, usually causing back pain and fever. A spread of bacteria from an untreated bladder infection is the most common cause of pyelonephritis.
- Glomerulonephritis: An overactive immune system may attack the kidney, causing inflammation and some damage. Blood in the urine and kidney failure are common symptoms of glomerulonephritis.
- Kidney stones (nephrolithiasis): Minerals in urine form crystals (stones), which may grow large enough to block urine flow. It's considered one of the most painful conditions. Most kidney stones pass on their own but some are too large and need to be treated.
- Nephrotic syndrome: Damage to the kidneys causes them to spill large amounts of protein into the urine. Leg swelling (edema) may be a symptom.
- Polycystic kidney disease: A genetic condition resulting in large cysts in both kidneys that impair their function.
- Acute renal failure (kidney failure): A sudden worsening in kidney function. Dehydration, a blockage in the urinary tract, or kidney damage can cause acute renal failure, which is usually reversible.
- Chronic renal failure: A permanent partial loss of kidney function. Diabetes and high blood pressure are the most common causes.
- End stage renal disease (ESRD): Complete loss of kidney function, usually due to progressive chronic kidney disease. People with ESRD require regular dialysis for survival.
- Papillary necrosis: Severe damage to the kidneys can cause chunks of kidney tissue to break off internally and clog the kidneys. If untreated, the resulting damage can lead to total kidney failure.
- Diabetic nephropathy: High blood sugar from diabetes progressively damages the kidneys, eventually causing chronic kidney disease. Protein in the urine (nephrotic syndrome) may also result.
- Hypertensive nephropathy: Kidney damage caused by high blood pressure. Chronic renal failure may eventually result.
- Kidney cancer: Renal cell carcinoma is the most common cancer affecting the kidney. Smoking is the most common cause of kidney cancer.
- Interstitial nephritis: Inflammation of the connective tissue inside the kidney, often causing acute renal failure. Allergic reactions and drug side effects are the usual causes.
- Minimal change disease: A form of nephrotic syndrome in which kidney cells look almost normal under the microscope. Steroids are used to treat minimal change disease, which can cause significant leg swelling (edema).
- Nephrogenic diabetes insipidus: The kidneys lose the ability to concentrate the urine, usually due to a drug reaction. Although it's rarely dangerous, diabetes insipidus causes constant thirst and frequent urination.
- Renal cyst: A benign hollowed-out space in the kidney. Isolated kidney cysts occur in many normal people and almost never impair kidney function.
- Urinalysis: A routine test of the urine by a machine and often by a person looking through a microscope. Urinalysis can help detect infections, inflammation, microscopic bleeding, and kidney damage.
- Kidney ultrasound: A probe placed on the skin reflects sound waves off the kidneys, creating images on a screen. Ultrasound can reveal blockages in urine flow, stones, cysts, or suspicious masses in the kidneys.
- Computed tomography ( CT scan): A CT scanner takes a series of X-rays and a computer creates detailed images of the kidneys.
- Magnetic resonance imaging ( MRI scan): A scanner uses radio waves in a magnetic field to make high-resolution images of the kidneys.
- Urine and blood cultures: If an infection is suspected, cultures of the blood and urine may identify the bacteria responsible. This can help target antibiotic therapy.
- Ureteroscopy: An endoscope (flexible tube with a camera on its end) is passed through the urethra into the bladder and ureters. Ureteroscopy generally cannot reach the kidneys themselves, but can help treat conditions that also affect the ureters.
- Kidney biopsy: Using a needle inserted into the back, a small piece of kidney tissue is removed. Examining the kidney tissue under a microscope may help diagnose a kidney problem.
- Antibiotics: Kidney infections caused by bacteria are treated with antibiotics. Often, cultures of the blood or urine can help guide the choice of antibiotic therapy.
- Nephrostomy: A tube (catheter) is placed through the skin into the kidney. Urine then drains directly from the kidney, bypassing any blockages in urine flow.
- Lithotripsy: Some kidney stones may be shattered into small pieces that can pass in the urine. Most often, lithotripsy is done by a machine that projects ultrasound shock waves through the body.
- Nephrectomy: Surgery to remove a kidney. Nephrectomy is performed for kidney cancer or severe kidney damage.
- Dialysis: Artificial filtering of the blood to replace the lost function of damaged kidneys. Hemodialysis is the most common method of dialysis in the U.S.
- Hemodialysis: A person with complete kidney failure is connected to a dialysis machine, which filters the blood and returns it to the body. Hemodialysis is typically done three days per week in people with ESRD.
- Peritoneal dialysis: Placing large amounts of a special fluid in the abdomen through a catheter, allows the body to filter the blood using the natural membrane lining the abdomen. After a while the fluid with the waste is drained and discarded.
- Kidney transplant: Transplanting a kidney into a person with ESRD can restore kidney function. A kidney may be transplanted from a living donor, or a recently deceased organ donor.