Chronic kidney disease (CKD) is a disease in which kidney function is declining. The kidney damage is irreversible, and uncontrolled CKD can lead to kidney failure and the need for kidney dialysis or a kidney transplant.
Humans have two fist-sized kidneys. These organs filter wastes and excess water from the blood to produce urine. The kidneys are responsible for maintaining chemical balances in the body, especially electrolytes such as sodium, calcium, potassium, and phosphate. They also produce hormones and help to control blood pressure. Damage to the kidneys causes CKD, in which the kidneys do not properly filter the blood. In addition to the buildup of waste products in the body, CKD can cause a variety of other health problems, including poor nutritional health, high blood pressure, anemia (low blood count), weakened bones, and nerve damage. CKD also increases the risk of heart and blood vessel disease. If CKD progresses to the point where the kidneys are badly damaged and stop functioning, patients develop kidney failure or end-stage renal disease (ESRD).
The major risk factors for CKD, at least in developed countries such as the United States, are diabetes, hypertension (high blood pressure), and obesity. Americans eat generally large amounts of sugar, which puts them at risk for diseases such as diabetes, hypertension, and heart disease, which are also risk factors for CKD. A family history of CKD and advanced age are risk factors. African Americans, Hispanics, Native Americans, and Asians are at higher risk for CKD.
Perfluorooctane sulfonate (PFOS) is a global persistent organic pollutant that was widely used in fabric protectors and stain repellents, It accumulates in the human body and is associated with an increased risk of CKD. It appears that, at least in developing countries, other unidentified environmental factors put people at risk for CKD. For example, agricultural workers in Sri Lanka and Central America have shown high levels of CKD. Although toxins could be the cause of some cases, researchers also believe that the workers have been subjected to repeated kidney injury from heat stress and lack of water leading to dehydration.
CKD is closely associated with diabetes, high blood pressure, and heart disease. As many as two-thirds of CKD cases are caused by diabetes and high blood pressure. High blood sugar from diabetes damages the kidneys, as well as other organs, and uncontrolled or poorly controlled hypertension also damages the kidneys. In addition to causing CKD, diabetes and obesity speed its progression. Furthermore, in addition to being caused by hypertension, CKD can cause high blood pressure. Infections and urinary blockages are other causes of CKD.
CKD is called the silent disease, because most people have no early symptoms. In fact, many people do not have any symptoms until their kidneys are about to fail. However, as CKD progresses, waste products build up in the body and act as poisons, causing symptoms of illness. These may include:
Early diagnosis of CKD is important for preventing its progression. Diagnosis usually begins with a medical history and a blood pressure test, since blood pressure above 120/80 can suggest the possibility of CKD. People with diabetes or prediabetes may be given an A1C test that measures their average blood glucose level over the past three months, since high blood sugar is a risk factor for CKD. CKD is then diagnosed by blood and urine tests that measure kidney function.
The estimated glomerular filtration rate (eGFR) is the most accurate test for CKD and also indicates the stage of CKD progression. The GFR measures how well the kidneys are filtering the blood. The eGFR is calculated from the serum level of creatinine, a waste product in the blood, and the patient's age, race, gender, and other factors. An eGFR of 60 or above is within the normal range. An eGFR below 60 for three months or longer can be a sign of kidney disease. An eGFR of 15 or below can indicate kidney failure.
Urine tests measure albumin, a protein in the blood that passes into the urine if the kidneys are damaged. Urine tests also indicate whether there is blood in the urine. Either protein or blood in the urine can be a sign of kidney disease. eGFR and urine albumin are also used to monitor CKD and assess the effectiveness of treatment.
Patients with CKD might be referred to a kidney specialist called a nephrologist. An ultrasound or computed tomography (CT) scan may be performed to visualize the kidneys and urinary tract and determine whether there is a structural problem or a kidney stone or tumor. Scans can also determine whether the kidneys are enlarged or are too small. Sometimes a kidney biopsy is performed by removing a small amount of kidney tissue for microscopic examination. A biopsy may be used to diagnose specific types of kidney disease, assess kidney damage, and help to plan a course of treatment.
The goal of CKD treatment is to prevent further reduction in the GFR. Treatment can significantly slow the progression of the disease and prevent or delay kidney failure, although it cannot reverse kidney damage. The most important treatment for slowing CKD is controlling high blood pressure. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin-II receptor blockers (ARBs) are blood pressure medicines that can slow CKD progression and delay kidney failure by lowering blood pressure. They are useful for treating CKD even in people who do not have high blood pressure. Often, two or more blood pressure medicines must be taken simultaneously. A diuretic or water pill may also be required. Medications for controlling or lowering blood sugar levels in diabetics and lowering blood cholesterol are also used to treat CKD.
Exercise and a healthy diet are essential for controlling blood sugar and blood pressure and can have a significant impact on CKD. People who smoke with CKD must quit smoking immediately, since smoking damages the kidneys, raises blood pressure, and interferes with the activities of blood pressure medications.
Patients with CKD must have regular kidney function tests and checkups to monitor for and treat other problems that can result from CKD. These include high triglyceride levels, a type of fat in the blood that is often higher in patients with kidney disease. CKD can also cause anemia, in which the blood does not have enough hemoglobin or red blood cells to efficiently carry oxygen throughout the body. Fatigue and weakness are symptoms of anemia. CKD may affect the utilization of calcium and phosphorus, resulting in weakened bones. It may be necessary for patients to avoid certain foods so that these minerals are better utilized.
Chichigalpa, a Nicaraguan city of almost 60,000 people, has stood out in the study of CKD around the world because hundreds or thousands of men have died of CKD. In all, more than 16,000 Central Americans, primarily male sugarcane workers, had died of CKD by late 2012. In El Salvador and Nicaragua, the death rate from CKD rose five-fold between 1992 and 2012. Many residents have believed CKD was caused by chemicals sprayed on sugarcane fields while the men were working or that the chemicals have seeped into the water supply. However, the sugar industry claimed that only acceptable amounts of standard fertilizers were used. The problem is considered a public health emergency, and a study of the workers revealed they were performing strenuous jobs in high heat. The men are paid by how much sugarcane they cut rather than by the hour, increasing the chance they would work through heat stress and fail to replace fluids and electrolytes essential for kidney health. Because it is the only employment available, many workers continue in the fields after being diagnosed with CKD. A 2016 study showed that these workers had high levels of uric acid and that loss of fluid volume is one cause of the high levels. The sugar industry, meanwhile, blamed the CKD epidemic on alcohol consumption among the workers or contamination of water supplies by active volcanoes.
High CKD rates have also been found in rural villages in India and among workers in Sri Lankan rice paddies. Research in Sri Lanka has indicated that chemicals may be causing the disease, specifically the heavy metals cadmium and arsenic that are present in fertilizers and pesticides. Although tested workers have shown levels of cadmium and arsenic below those that the World Health Organization officially designates as dangerous, some researchers believe that long-term exposure, most likely through the food chain, is probably responsible for the CKD epidemics. A 2018 study found no solid evidence for heat stress, although the authors said more study is needed.
Kidney damage from CKD is usually irreversible. CKD is a progressive disease that, without treatment, worsens over time, eventually leading to kidney failure that requires dialysis or a kidney transplant. For some patients, CKD progresses rapidly to kidney failure. However, with treatment, including medications, diet, and lifestyle changes, patients can survive for many years without having dialysis. Unfortunately, many people with CKD do not receive treatment. Furthermore, CKD patients may develop anemia, bone disease, heart and blood vessel disease, or other conditions.
Several studies have suggested that people who drink more fluids might have a significantly lower risk of CKD than those who drink less. Other measures for preventing CKD or slowing its progression are:
See also Arsenic ; Cadmium ; Cadmium poisoning ; Chemical poisoning .
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American Kidney Fund, 11921 Rockville Pike, Ste. 300, Rockville, MD, 20852, (800) 638-8299, http://www.kidneyfund.org .
National Institute of Diabetes and Digestive and Kidney Diseases, Office of Communications & Public Liaison, NIDDK, NIH Bldg. 31, Rm. 9A06, 31 Center Dr., MSC 2560, Bethesda, MD, 20892-2560, (800) 860-8747, http://www2.niddk.nih.gov .
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National Kidney Foundation, 30 E. 33rd St., New York, NY, 10016, (800) 622-9010, Fax: (212) 689-9261, http://www.kidney.org .
Margaret Alic, PhD
Revised by Teresa Odle, BA, ELS