What is Chronic Kidney Disease?

In chronic kidney disease, the kidneys get damaged over time and increasingly lose their function of filtering the blood.

Healthy kidneys filter about 200 liters (just over 52 gallons) of blood daily, and make about 2 liters (a little over half a gallon) of urine containing excess water and waste products.

Important functions of the kidneys include:

• Filtering out excess water and waste products
• Helping maintain blood pressure
• Helping maintain red blood cell production
• Helping balance minerals in the blood

In chronic kidney disease, the kidneys get increasingly damaged and the filtering capacity is lost over time.

The disease is diagnosed by checking the blood and analyzing how well it is being filtered. One measure of that is the estimated glomerular filtration rate (eGFR) test. The number of the eGFR value corresponds to the percentage of kidney function. At eGFR of 100 mL/min/1.73 m², the patient has about 100% kidney function. At eGFR of 30 mL/min/1.73 m², the patient has about 30% kidney function. An eGFR of less than 60 mL/min/1.73 m² indicating less than 60% kidney function persisting for 3 months or longer indicates kidney disease.

Other markers for kidney disease include blood or protein in the urine. The patient may also be tested for diabetes and high blood pressure, which are major causes of kidney disease.

Prevalence

The CDC estimates that 1 in 7 US adults (35.5 million people) have chronic kidney disease. However, 90% of US adults who have the disease are unaware of it. One in three adults with severe chronic kidney disease is also unaware of it.
The disease is more likely in adults over 65. It is the most common in non-Hispanic Black adults (20%) followed by non-Hispanic Asian adults and Hispanic adults (13.7% each), and non-Hispanic White adults (11.7%).

Stages of chronic kidney disease

Chronic kidney disease has been divided into 5 stages. Stage 1 has the least kidney damage and stage 5 has the most kidney damage where kidneys have already failed or are close to failing. The stages are based on the EGFR values measured in units of mL/min/1.73 m².

Stage 1. Mild kidney disease; EGFR ≥ 90.

Stage 2. More signs of mild kidney disease; EGFR is 60-89.

Stage 3a. Mild to moderate kidney disease, symptoms first start showing; EGFR is 45-59.

Stage 3b. Moderate kidney disease; EGFR is 30-44.

Stage 4. Severe kidney disease; EGFR is 15-29.

Stage 5. Severely damaged kidneys that have failed or are close to failing; EGFR is 15-29.

Symptoms of chronic kidney disease

Early and mild kidney disease would not typically cause symptoms. It can take a long time for enough waste products to build up in the blood for specific symptoms to present. As kidney disease gets worse, the patient may experience one or more of these symptoms:

1. Edema. Edema is the swelling in the legs, feet, ankles, hands, or face due to the failure of kidneys to remove excess fluid and salt.
2. Chronic kidney disease-associated pruritus (CKD-aP). CKD-aP is very itchy skin that occurs because of high levels of waste products in the blood such as parathyroid hormone, calcium, phosphorus, magnesium, or aluminum. It can also be due to high levels of histamines, shrinking sweat glands, and nerve damage caused by chronic kidney disease. The intensity of itchiness and how often it is experienced varies from patient to patient. This symptom can sometimes be experienced even in early kidney disease.
3. Chest pain. In late-stage kidney disease, fluid can build up around the heart causing chest pain.
4. Weakness, exhaustion, trouble sleeping and concentrating. These symptoms are caused by the buildup of toxins in the blood.
5. Headaches. The buildup of toxins, oxidative stress, and fluctuations in blood pressure can cause headaches.
6. More or less urine production than normal. Daily urine production can increase when the kidneys cannot filter water out of urine effectively. Due to dehydration and kidney damage, urine production may also decrease.
7. Loss of appetite. The reduced efficiency of the kidneys creates an imbalance of hormones and other metabolites that pass into the brain and generate signals of hunger. This leads to anorexia and unhealthy weight loss. Patients may need an increased frequency of dialysis and appetite-stimulant medications.
8. Pain. Musculoskeletal pain (pain in muscles, tendons, ligaments, joints, or bones) originating from tissue damage may be experienced in advanced kidney disease. According to one report, 60-70% of patients with advanced kidney disease and 100% of patients who were hospitalized for advanced kidney disease experienced musculoskeletal pain. Constant pain can also cause secondary problems such as depression and anxiety.
9. Nausea and vomiting. 30-43% of patients with advanced kidney disease experience nausea and vomiting possibly due to metabolic or gastrointestinal disturbances or as a side effect of medications.
10. Shortness of breath. Patients may experience shortness of breath due to fluid buildup in the lungs or an imbalance of nutrients and metabolites in the blood.

What are the causes of chronic kidney disease?

Uncontrolled diabetes and high blood pressure are the main causes of chronic kidney disease. Other causes include polycystic kidney disease, autoimmune diseases such as lupus, infections, and ingestion of drugs or toxins that harm the kidneys.

Management of chronic kidney disease

Managing chronic kidney disease with your medical team can prevent the disease from getting worse.

Disease management includes controlling hypertension and diabetes, and staying on top of the prescribed medications. Speak to your doctor about any foods or over-the-counter medications you should avoid to protect your kidneys.