Understanding Kidney Disease

It is estimated that kidney disease affects 31 million people in the United States alone, and globally 1 in 10 people have some form of kidney disease. Also called renal disease, kidney disease is the general term for damage that reduces function of the kidney.  Chronic kidney disease (CKD) occurs when kidneys are no longer able to clean toxins and waste product from the blood and perform their functions to full capacity. This can happen all of a sudden or over time.¹ Chronic kidney disease (CKD) has five distinct stages.

Every day, our two kidneys filter about 120 to 150 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra fluid.² Healthy kidneys help regulate blood pressure, remove waste and water, signal your body to make red blood cells, and help regulate growth in children.

In addition to the different phases of chronic kidney disease, or CKD (listed below), there are different types of kidney disease, with different causes and requiring different treatments. NKI and this website provide detailed information about the diseases that cause Nephrotic Syndrome (NS) and Focal Segmental Glomerulosclerosis (FSGS).

Five Stages of Kidney Disease

The National Kidney Foundation (NKF) created a guideline to help doctors identify each level of kidney disease. The NKF divided kidney disease (CKD) into five stages. Identifying the stage of kidney disease a person is in helps health care practitioners provide the best care, since each stage requires different treatment.

To understand each stage, we must first understand how kidney function is measured. The universally accepted measure of kidney function is the Glomerular Filtration Rate (GFR). Kidney function is measured by how effectively your kidneys clean your blood. The main way of estimating GFR is a blood test to determine the level of Creatinine in the blood, or serum creatinine. As kidney function declines, the levels of creatinine increase.

An equation is used to determine GFR. In addition to serum creatinine, factors such as age, race, and gender are included in the equation. Additional factors that may be included are weight, blood urea nitrogen (BUN), and serum albumin.

The five stages of kidney disease, or CKD, and the GFR for each stage, is shown below:

• Stage 1 with normal or high GFR (GFR > 90 mL/min)
• Stage 2 Mild CKD (GFR = 60-89 mL/min)
• Stage 3A Moderate CKD (GFR = 45-59 mL/min)
• Stage 3B Moderate CKD (GFR = 30-44 mL/min
• Stage 4 Severe CKD (GFR = 15-29 mL/min)
• Stage 5 End Stage CKD (GFR <15 mL/min)

What is the Function of Our Kidneys?

The kidneys are a very important organ in the body. They are two bean-shaped organs, each about the size of a fist, located just below the rib cage, one on each side of your spine. The kidneys are responsible for getting rid of waste products, drugs, and toxins through our urine.

Your kidneys also:

• Regulate electrolyte (salt) concentrations
• Regulate amount of fluid within the body
• Help regulate blood pressure
• Help maintain acid-base balance
• Produce hormones that affect blood and bones
• A kidney is composed of tiny units called nephrons
• Nephrons consist of glomeruli and tubules
• Glomeruli are small blood vessels that filter wastes and excess fluids
• Tubules collect the waste to form urine

What Causes Sudden Kidney Injury?

The sudden loss of kidney function is called acute kidney injury (AKI).

AKI can occur following:

• A traumatic injury with blood loss
• The sudden reduction of blood flow to the kidneys
• Damage to the kidneys during a severe infection or virus
• Obstruction of urine flow
• Damage from certain drugs or toxins
• Pregnancy complications, such as eclampsia and pre-eclampsia, or related HELLP Syndrome

What is Chronic Kidney Disease?

Kidney damage and decreased function that lasts longer than 3 months is called chronic kidney disease (CKD). Chronic kidney disease is particularly dangerous because you may not have any symptoms until considerable, often irreparable, kidney damage has occurred. Diabetes (types 1 and 2) and high blood pressure are the most common causes of CKD.

Other causes are:

• Immune system conditions such as lupus and chronic viral illnesses such as HIV/AIDS, hepatitis B, and hepatitis C.
• Urinary tract infections within the kidneys themselves, called pyelonephritis, can lead to scarring as the infection heals. Multiple episodes can lead to kidney damage.
• Inflammation in the tiny filters (glomeruli) within the kidneys; this can happen after strep infection and other conditions of unknown cause. (Glomerular Disease)
• Polycystic kidney disease, in which fluid-filled cysts form in the kidneys over time. This is the most common form of inherited kidney disease.
• Congenital defects, present at birth, are often the result of a urinary tract obstruction or malformation that affects the kidneys. One of the most common involves a valve-like mechanism between the bladder and urethra.
• Drugs and toxins, including long-term exposure to some medications and chemicals, such as NSAIDs (nonsteroidal anti-inflammatory drugs), like ibuprofen and naproxen, and use of intravenous “street” drugs.
• For a comprehensive guide to all types of kidney disease and related topics, visit http://www.kidney.org/atoz/.

To learn more about specific types of rare, protein-spilling kidney diseases, visit our pages focused on Nephrotic Syndrome (NS), Focal Segmental Glomerulosclerosis (FSGS), and Minimal Change Disease (MCD).

Additional Resources

• Davita Chronic Kidney Disease Resources