Common Questions About Kidney Disease
What Is Chronic Kidney Disease?
Chronic kidney disease occurs when one suffers from gradual and usually permanent loss of kidney function over time. This happens gradually, usually over months to years. Chronic kidney disease is divided into five stages of increasing severity:
Stage I: Slight damage to the kidney(s) damage
Stage II: Mild decrease in kidney function
Stage III: Moderate decrease in kidney function
Stage 4: Severe decrease in kidney function
Stage 5: Kidney failure
With loss of kidney function, there is an accumulation of water, waste, and toxic substances in the body that are normally excreted by the kidney. Loss of kidney function also causes other problems such as anemia, high blood pressure, acidosis (excessive acidity of body fluids), disorders of cholesterol and fatty acids, and bone disease.
The term "renal" refers to the kidney, so another name for kidney failure is "renal failure." Mild kidney disease is often called renal insufficiency.
Where Are the Kidneys Located? What Do They Look Like?
Normal kidneys and kidney function
The kidneys are a pair of bean-shaped organs that lie on either side of the spine in the lower middle of the back.
Each kidney weighs about 5 ounces and contains approximately one million filtering units called nephrons.
Each nephron is made of a glomerulus and a tubule. The glomerulus is a miniature filtering or sieving device while the tubule is a tiny tube like structure attached to the glomerulus.
The kidneys are connected to the urinary bladder by tubes called ureters. Urine is stored in the urinary bladder until the bladder is emptied by urinating. The bladder is connected to the outside of the body by another tube like structure called the urethra.
The main function of the kidneys is to remove waste products and excess water from the blood. The kidneys process about 200 liters of blood every day and produce about 2 liters of urine. The waste products are generated from normal metabolic processes including the breakdown of active tissues, ingested foods, and other substances. The kidneys allow consumption of a variety of foods, drugs, vitamins, dietary and herbal supplements, food additives, and excess fluids without worry that toxic by-products will build up to harmful levels. The kidney also plays a major role in regulating levels of various minerals such as calcium, sodium, and potassium in the blood.
As the first step in filtration, blood is delivered into the glomeruli by microscopic leaky blood vessels called capillaries. Here, blood is filtered of waste products and fluid while red blood cells, proteins, and large molecules are retained in the capillaries. In addition to wastes, some useful substances are also filtered out. The filtrate collects in a sac called Bowman's capsule.
The tubules are the next step in the filtration process. The tubules are lined with highly functional cells which process the filtrate, reabsorbing water and chemicals useful to the body while secreting some additional waste products into the tubule.
The kidneys also produce certain hormones that have important functions in the body, including the following:
Active form of vitamin D (calcitriol or 1,25 dihydroxy-vitamin D), which regulates absorption of calcium and phosphorus from foods, promoting formation of strong bone.Erythropoietin (EPO), which stimulates the bone marrow to produce red blood cells.
Renin, which regulates blood volume and blood pressure in association with aldosterone manufactured in the adrenal glands, located just above the kidneys.
What Tests and Procedures Diagnose Chronic Kidney Disease?
Chronic kidney disease usually causes no symptoms in its early stages. Only lab tests can detect any developing problems. Anyone at increased risk for chronic kidney disease should be routinely tested for development of this disease.Urine, blood, and imaging tests (X-rays) are used to detect kidney disease, as well as to follow its progress.All of these tests have limitations. They are often used together to develop a picture of the nature and extent of the kidney disease.In general, this testing can be performed on an outpatient basis.
Urine tests
Urinalysis: Analysis of the urine affords enormous insight into the function of the kidneys. The first step in urinalysis is doing a dipstick test. The dipstick has reagents that check the urine for the presence of various normal and abnormal constituents including protein. Then, the urine is examined under a microscope to look for red and white blood cells, and the presence of casts and crystals (solids).Only minimal quantities of albumin (protein) are present in urine normally. A positive result on a dipstick test for protein is abnormal. More sensitive than a dipstick test for protein is a laboratory estimation of the urine albumin (protein) and creatinine in the urine. The ratio of albumin (protein) and creatinine in the urine provides a good estimate of albumin (protein) excretion per day.
Twenty-four hour urine tests: This test requires the patient to collect all of their urine for 24 consecutive hours. The urine may be analyzed for protein and waste products (urea nitrogen, and creatinine). The presence of protein in the urine indicates kidney damage. The amount of creatinine and urea excreted in the urine can be used to calculate the level of kidney function and the glomerular filtration rate (GFR).
Glomerular filtration rate (GFR): The GFR is a standard means of expressing overall kidney function. As kidney disease progresses, GFR falls. The normal GFR is about 100 to 140 mL/min in men and 85 to 115 mL/min in women. It decreases in most people with age. The GFR may be calculated from the amount of waste products in the 24-hour urine or by using special markers administered intravenously. An estimation of the GFR (eGFR) can be calculated from the patient's routine blood tests. It is not as accurate in patients younger than 18, pregnant patients, and those who are very muscular or who are very overweight. Patients are divided into five stages of chronic kidney disease based on their GFR (see Table 1 above).
Blood tests
Creatinine and urea (BUN) in the blood: Blood urea nitrogen and serum creatinine are the most commonly used blood tests to screen for and monitor renal disease. Creatinine is a product of normal muscle breakdown. Urea is the waste product of breakdown of protein. The level of these substances rises in the blood as kidney function worsens.
Estimated GFR (eGFR): The laboratory or physician may calculate an estimated GFR using the information from a patient's blood work. It is not as accurate in patients younger than 18, pregnant patients, and those who are very muscular and those who are very overweight. It is important to be aware of one's estimated GFR and stage of chronic kidney disease. The physician uses the patient's stage of kidney disease to recommend additional testing and provide suggestions on management.
Electrolyte levels and acid-base balance: Kidney dysfunction causes imbalances in electrolytes, especially potassium, phosphorus, and calcium. High potassium (hyperkalemia) is a particular concern. The acid-base balance of the blood is usually disrupted as well.Decreased production of the active form of vitamin D can cause low levels of calcium in the blood. Inability of failing kidneys to excrete phosphorus causes its levels in the blood to rise. Testicular or ovarian hormone levels may also be abnormal.
Blood cell counts: Because kidney disease disrupts blood cell production and shortens the survival of red cells, the red blood cell count and hemoglobin may be low (anemia). Some patients may also have iron deficiency due to blood loss in their gastrointestinal system. Other nutritional deficiencies may also impair the production of red cells.
Other tests
Ultrasound: Ultrasound is often used in the diagnosis of kidney disease. An ultrasound is a noninvasive type of imaging test. In general, kidneys are shrunken in size in chronic kidney disease, although they may be normal or even large in size in cases caused by adult polycystic kidney disease, diabetic nephropathy, and amyloidosis. Ultrasound may also be used to diagnose the presence of urinary obstruction, kidney stonesand also to assess the blood flow into the kidneys.
Biopsy: A sample of the kidney tissue (biopsy) is sometimes required in cases in which the cause of the kidney disease is unclear. Usually, a biopsy can be collected with local anesthesia by introducing a needle through the skin into the kidney. This is usually done as an outpatient procedure, though some institutions may require an overnight hospital stay.
Can Chronic Kidney Disease be Prevented?
Chronic kidney disease cannot be prevented in most situations. The patient may be able to protect their kidneys from damage, or slow the progression of the disease by controlling their underlying conditions such as diabetes mellitus and high blood pressure.
Kidney disease is usually advanced by the time symptoms appear. If a patient is at high risk of developing chronic kidney disease, they should see their doctor as recommended for screening tests.
If a patient has a chronic condition such as diabetes, high blood pressure, or high cholesterol, they should follow the treatment recommendations of their health care practitioner. The patient should see their health care practitioner regularly for monitoring. Aggressive treatment of these diseases is essential.
The patient should avoid exposure to drugs especially NSAIDs (nonsteroidal anti-inflammatory drugs), chemicals, and other toxic substances as much as possible.