Kidney Disease Glossary

Medical terminology can be intimidating. This glossary defines over 60 common kidney disease terms in plain language — so you can understand what your doctor is saying, read your lab reports with confidence, and feel less overwhelmed by the vocabulary of kidney care.

A

ACE Inhibitor: A type of blood pressure medication (e.g., lisinopril, enalapril) that also protects the kidneys by reducing pressure inside the glomeruli. Often prescribed for CKD patients, especially those with diabetes or proteinuria.
Acute Kidney Injury (AKI): A sudden loss of kidney function, usually occurring over hours or days. Unlike CKD, AKI is often reversible with prompt treatment. Causes include severe dehydration, infections, and certain medications.
Albumin: A protein made by the liver that circulates in the blood. When found in urine (albuminuria), it is an early sign of kidney damage. Healthy kidneys do not let albumin pass into urine.
Albuminuria: The presence of albumin (protein) in the urine. A key marker for kidney damage and a sign that the kidney's filtering system is leaking. Measured by the uACR test. Learn more →
Albuminuria Categories (A1–A3): A classification system for the severity of albuminuria. A1 (normal, below 30 mg/g) means minimal protein leak. A2 (moderately increased, 30–300 mg/g) signals early kidney damage. A3 (severely increased, above 300 mg/g) indicates significant damage. Used alongside G stages to classify CKD. Learn more →
Anaemia (Anemia): A condition where you do not have enough red blood cells to carry adequate oxygen to your tissues. Common in CKD because the kidneys produce less erythropoietin (EPO), the hormone that stimulates red blood cell production.
ARB: Angiotensin II Receptor Blocker — a blood pressure medication (e.g., losartan, valsartan) with kidney-protective effects similar to ACE inhibitors. Used when ACE inhibitors cause side effects like cough.
Arteriovenous Fistula (AV Fistula): A surgically created connection between an artery and a vein, usually in the arm, used for haemodialysis access. Considered the best long-term access option. Needs 2–6 months to mature before use. Learn more →

B

Bicarbonate: A substance that helps keep your blood at a healthy pH level (not too acidic). The kidneys normally produce bicarbonate. In advanced CKD, bicarbonate levels drop, leading to metabolic acidosis. Often supplemented with sodium bicarbonate tablets.
BUN (Blood Urea Nitrogen): A blood test that measures the amount of urea nitrogen in your blood. Urea is a waste product from protein metabolism. Elevated BUN can indicate reduced kidney function, but it is also affected by diet and hydration. Learn more →

C

Calcium: A mineral essential for bones, muscles, and nerves. In CKD, calcium levels can become abnormal because the kidneys can no longer activate vitamin D properly. Low calcium can lead to bone weakness and is part of the CKD-MBD picture.
Catheter (Dialysis): A flexible tube inserted into a large vein (usually in the neck or chest) to provide temporary access for haemodialysis. Used when a fistula or graft is not yet ready. Learn more →
CGA Staging: The complete CKD classification system that combines three factors: Cause of kidney disease (C), GFR category G1–G5 (G), and Albuminuria category A1–A3 (A). This gives your care team a full picture of your kidney health, not just one number. Learn more →
CKD (Chronic Kidney Disease): A progressive condition in which the kidneys gradually lose their ability to filter waste and excess fluid from the blood. Defined as kidney damage or GFR below 60 for three months or more. Classified in 5 stages based on GFR. Learn more →
CKD-MBD (Mineral and Bone Disorder): A group of problems with calcium, phosphorus, PTH, and vitamin D that develop as kidney function declines. CKD-MBD weakens bones, causes itching, and can damage blood vessels. Managed through diet, phosphate binders, and vitamin D.
CKD Staging (G1–G5): CKD is classified into five stages based on GFR: G1 (≥90, normal GFR with other signs of damage), G2 (60–89, mildly decreased), G3a (45–59, mild-to-moderate), G3b (30–44, moderate-to-severe), G4 (15–29, severely decreased), G5 (<15, kidney failure). Each stage guides treatment decisions. Learn more →
Creatinine: A waste product produced by your muscles that is filtered by the kidneys. Blood creatinine levels are used to estimate GFR. Higher creatinine generally means lower kidney function, though muscle mass and other factors affect the number. Learn more →

D

Deceased Donor: A person who has died and whose kidneys are donated for transplantation. Deceased donor kidneys last an average of 10–15 years. The waiting list for a deceased donor kidney can be 3–7 years depending on blood type and location. Learn more →
Diabetes Mellitus: A condition where the body cannot properly regulate blood sugar. Type 1 and Type 2 diabetes are the leading cause of CKD worldwide. High blood sugar damages the tiny blood vessels in the kidneys over time (diabetic nephropathy). Learn more →
Dialysis: A medical treatment that performs the functions of the kidneys when they can no longer work adequately. The two main types are haemodialysis (filtering blood through a machine) and peritoneal dialysis (using the lining of the abdomen). Learn more →
Dialysis Adequacy: A measure of whether dialysis is removing enough waste from your body. Assessed using Kt/V or URR (urea reduction ratio). Your care team monitors this regularly to ensure your treatments are effective.

E

Edema (Oedema): Swelling caused by excess fluid trapped in your body's tissues. In kidney disease, oedema commonly affects the ankles, feet, legs, hands, and face. It occurs when the kidneys cannot remove enough fluid. Learn more →
eGFR (Estimated Glomerular Filtration Rate): A calculated estimate of how well your kidneys filter blood, derived from your blood creatinine level, age, and sex. The most important number for staging CKD. Normal is above 90 mL/min. Learn more →
Electrolytes: Minerals in your blood that carry an electric charge, including potassium, sodium, calcium, and phosphorus. The kidneys help maintain electrolyte balance. Imbalances are common in CKD and can be dangerous. Learn more →
EPO (Erythropoietin): A hormone produced by the kidneys that stimulates the bone marrow to produce red blood cells. Declining EPO production in CKD leads to anaemia. Synthetic EPO (epoetin alfa, darbepoetin) can be given as treatment.
ESKD (End-Stage Kidney Disease): The final stage of chronic kidney disease (stage 5, also called ESRD) where kidney function has declined to the point that dialysis or a transplant is needed to sustain life. GFR is typically below 15 mL/min. Learn more →

F

Finerenone: A newer medication (non-steroidal mineralocorticoid receptor antagonist) approved for slowing the progression of kidney disease in patients with type 2 diabetes and CKD. Used alongside ACE/ARBs and SGLT2 inhibitors.
Fluid Restriction: A limit on how much liquid you drink each day. May be necessary in advanced CKD or on dialysis when the kidneys can no longer remove enough fluid. Your care team sets a daily limit based on urine output, weight gain, and blood pressure.

G

G3a and G3b: Sub-stages of CKD stage 3. G3a (GFR 45–59) is mild-to-moderately decreased kidney function. G3b (GFR 30–44) is moderate-to-severely decreased. The split matters because G3b patients have a significantly higher risk of progressing to kidney failure and are typically monitored more closely. Learn more →
GFR (Glomerular Filtration Rate): The rate at which your kidneys filter blood, measured in milliliters per minute. The gold standard for assessing kidney function. Usually estimated from blood tests (eGFR) rather than measured directly. Learn more →
Glomerulus: A tiny cluster of blood vessels inside each nephron that acts as the kidney's primary filter. Each kidney contains about 1 million glomeruli. Damage to the glomeruli is a primary mechanism in many forms of kidney disease.
Graft (Dialysis): A synthetic tube connecting an artery to a vein, used as an alternative to a fistula for haemodialysis access. Grafts can be used sooner than fistulas (within 2–4 weeks) but have a higher rate of complications. Learn more →

H

Haematuria: The presence of blood in the urine. Visible haematuria (you can see it) makes urine look pink, red, or brown. Microscopic haematuria (invisible to the eye) is detected only by lab tests. Can indicate kidney disease, infection, or other urological conditions.
Haemodialysis: A type of dialysis where blood is pumped through an external machine (dialyser) that filters waste and excess fluid. Typically performed 3 times per week at a dialysis centre, each session lasting 3–5 hours. Learn more →
Hyperkalaemia (Hyperkalemia): Abnormally high potassium levels in the blood (above 5.0 mEq/L). A potentially dangerous condition in kidney disease because high potassium can cause irregular heartbeat or cardiac arrest. Learn more →
Hypertension: High blood pressure — a leading cause and consequence of CKD. The target for most CKD patients is below 130/80 mmHg. Managing blood pressure is one of the most effective ways to slow kidney disease progression. Learn more →

I

Immunosuppression: Medications that suppress the immune system to prevent it from attacking a transplanted kidney. Required for life after kidney transplant. Common drugs include tacrolimus, mycophenolate, and prednisone. Learn more →

K

KDIGO: Kidney Disease: Improving Global Outcomes — an international organisation that develops clinical practice guidelines for kidney disease. KDIGO guidelines are the global standard for CKD classification and treatment.
Kidney Biopsy: A procedure where a small sample of kidney tissue is removed with a needle and examined under a microscope. Used to diagnose the specific cause of kidney disease and guide treatment decisions.
Kidney Failure: When the kidneys can no longer function well enough to sustain health — also called ESKD or stage 5 CKD. GFR is below 15 mL/min. Treatment (dialysis or transplant) is needed. Many people live full lives with kidney failure when properly treated. Learn more →
Kidney Transplant: A surgery in which a healthy kidney from a living or deceased donor is placed into a patient with kidney failure. Offers the best long-term outcomes for most patients and eliminates the need for dialysis. Learn more →

L

Living Donor: A person who donates one of their kidneys while alive, usually to a family member, friend, or through a paired exchange programme. Living donor kidneys last an average of 15–20 years — longer than deceased donor kidneys. Learn more →
Low Potassium Diet: A dietary approach that limits potassium intake, typically to 2,000–3,000 mg per day. Not all CKD patients need this restriction — it depends on blood potassium levels. Focuses on choosing lower-potassium fruits, vegetables, and proteins. Learn more →

M

Metabolic Acidosis: A condition where the blood becomes too acidic because the kidneys can no longer remove enough acid or produce enough bicarbonate. Common in CKD stages 4–5. Symptoms include rapid breathing and fatigue. Treated with sodium bicarbonate supplements.

N

Nephron: The basic functional unit of the kidney. Each kidney contains about 1 million nephrons, each consisting of a glomerulus (filter) and a tubule (tube). Nephrons filter blood, reabsorb useful substances, and produce urine.
Nephrologist: A doctor who specialises in kidney disease. Nephrologists manage CKD, perform kidney biopsies, oversee dialysis, and coordinate transplant evaluations. Most CKD patients are referred to a nephrologist by stage 3–4. Learn more →
Nephropathy: A general term for kidney disease or damage. Diabetic nephropathy is kidney damage caused by diabetes — the leading cause of kidney failure worldwide. Learn more →
Nocturia: The need to wake up during the night to urinate. Common in CKD because damaged kidneys lose the ability to concentrate urine, producing more dilute urine throughout the day and night.

P

Peritoneal Dialysis (PD): A type of dialysis performed at home, using the lining of your abdomen (peritoneum) as a natural filter. A special fluid is introduced through a catheter and absorbs waste before being drained. Usually performed daily. Learn more →
Phosphate Binder: A medication taken with meals to prevent your body from absorbing too much phosphorus from food. Necessary when the kidneys can no longer remove enough phosphorus. Common binders include sevelamer and calcium acetate.
Phosphorus: A mineral found in many foods (dairy, meat, processed foods) that can build up in the blood when kidneys fail. High phosphorus causes itching, weakens bones, and damages blood vessels. Learn more →
PKD (Polycystic Kidney Disease): An inherited condition where clusters of fluid-filled cysts develop in the kidneys, gradually enlarging them and reducing function. The most common inherited cause of kidney failure.
Potassium: An essential mineral that helps regulate heartbeat, muscle function, and nerve signals. In CKD, the kidneys may not remove enough potassium, leading to dangerous buildup (hyperkalaemia). Learn more →
Proteinuria: The presence of excess protein in the urine. A sign of kidney damage. Protein in the urine (especially albumin) indicates that the kidney's filters are leaking and is a risk factor for faster kidney disease progression. Learn more →
PTH (Parathyroid Hormone): A hormone produced by the parathyroid glands that regulates calcium and phosphorus. In CKD, PTH levels rise because the kidneys cannot maintain normal calcium and phosphorus balance. High PTH weakens bones and is part of CKD-MBD.

R

Renal: Relating to the kidneys. 'Renal function' means kidney function. 'Renal diet' means a diet designed for kidney patients. 'Renal failure' means kidney failure.
Renal Diet: A way of eating designed to reduce the workload on damaged kidneys. Depending on your CKD stage, it may involve managing potassium, phosphorus, sodium, protein, and fluid intake. A renal dietitian creates a personalised plan based on your lab results. Learn more →
Renal Dietitian: A registered dietitian who specialises in nutrition for kidney disease patients. They create personalised meal plans that manage potassium, phosphorus, sodium, protein, and fluid based on your CKD stage and lab results. Learn more →
Renal Osteodystrophy: A bone disease that develops in CKD due to imbalances in calcium, phosphorus, PTH, and vitamin D. Bones become weak, thin, or misshapen. Part of the broader CKD-MBD syndrome. Managed with phosphate binders, vitamin D, and sometimes calcimimetics.

S

SGLT2 Inhibitor: A class of medications (e.g., dapagliflozin, empagliflozin) originally developed for diabetes that have shown remarkable kidney-protective effects. They slow CKD progression by 30–40% and are now recommended for most CKD patients. Learn more →
Sodium: A mineral found in salt and many processed foods. In CKD, excess sodium causes fluid retention, raises blood pressure, and makes the kidneys work harder. Most CKD patients are advised to limit sodium to under 2,000 mg per day. Learn more →

U

uACR (Urine Albumin-to-Creatinine Ratio): A urine test that measures the ratio of albumin (protein) to creatinine. Used to detect early kidney damage. A result above 30 mg/g is considered abnormal. One of the most important screening tests for diabetic kidney disease. Learn more →
Ultrasound (Renal): A painless imaging test that uses sound waves to create pictures of your kidneys. Shows kidney size, shape, and structure. Used to check for cysts, stones, blockages, or other abnormalities. Often one of the first tests in a kidney disease workup.
Urea: A waste product created when the body breaks down protein. Healthy kidneys filter urea from the blood into urine. When kidney function declines, urea builds up — measured by the BUN (blood urea nitrogen) test. Learn more →
Uraemia (Uremia): The buildup of waste products (urea and other toxins) in the blood when the kidneys can no longer filter them adequately. Symptoms include fatigue, nausea, mental fogginess, and itching. Treatment is dialysis or transplant. Learn more →

V

Vascular Access: The site on your body where blood is removed and returned during haemodialysis. The three types are fistula, graft, and catheter. A well-functioning access is essential for effective dialysis. Learn more →

W

Waiting List: The national registry of patients approved for a deceased donor kidney transplant. Time on the list depends on blood type, antibodies, location, and other medical factors. Average wait is 3–7 years. You can be listed while still on dialysis or even before starting. Learn more →

Educational information only. This glossary provides simplified definitions for general understanding. Discuss your results and treatment with your clinician. Read our editorial policy.