Plain-language kidney glossary
47 medical terms translated into words a patient actually understands.
Albumin
A protein your blood needs to carry nutrients and keep fluid in the right places. When your kidneys are damaged, albumin leaks into urine — a sign called proteinuria.
Clinically, a serum albumin below 3.5 g/dL in dialysis patients is associated with higher mortality and inflammation; it is monitored monthly.
Anemia of CKD
Low red blood cell count caused by failing kidneys that no longer make enough EPO (a hormone that tells bone marrow to produce red cells). You feel exhausted and short of breath.
Treated with erythropoiesis-stimulating agents (ESAs) and iron; target hemoglobin is typically 10–11 g/dL per KDIGO guidelines for dialysis patients.
Arteriovenous (AV) FistulaAV Fistula
A surgically created connection between an artery and a vein — usually in your forearm. It makes one vein stronger and larger so needles can be inserted for dialysis. Considered the gold standard of access.
Requires 6–12 weeks to mature before use; a "thrill" (buzzing sensation) and "bruit" (whooshing sound) confirm it is functioning.
Blood Pressure (renal context)
Kidney disease and high blood pressure form a dangerous cycle — damaged kidneys raise blood pressure, and high blood pressure damages kidneys further. Control is critical at every CKD stage.
Target BP for most CKD patients is below 130/80 mmHg per KDIGO 2021 guidelines; volume removal during dialysis is a primary tool for BP management.
BUNBlood Urea Nitrogen
A measure of waste product (urea) in your blood. When kidneys fail, they stop filtering urea out, so BUN climbs. High BUN means your kidneys are not cleaning your blood well.
Normal BUN is 7–20 mg/dL; pre-dialysis levels are expected to be higher; the ratio of pre- to post-dialysis BUN helps calculate Kt/V adequacy.
Calcium
A mineral that keeps your bones strong and your heart rhythm steady. CKD disrupts how your body absorbs calcium, often causing levels to drop too low — which weakens bones over time.
Dialysis patients are monitored for hypocalcemia and hypercalcemia; calcium-based phosphate binders can raise calcium, requiring careful dosing with serum levels typically targeted at 8.4–9.5 mg/dL.
Catheter (Tunneled / Temporary)
A tube inserted into a large neck or chest vein to allow dialysis when a fistula or graft is not ready. Temporary catheters go in fast but carry higher infection risk. Tunneled catheters sit under the skin and last longer.
Catheters have the highest rates of bacteremia among dialysis access types; transition to fistula or graft is prioritized due to the "Fistula First, Catheter Last" initiative.
CKDChronic Kidney Disease
Long-term kidney damage that does not go away. Kidneys gradually lose their ability to filter waste, balance fluids, and regulate blood pressure. Classified in 5 stages based on how well the kidneys still work.
Defined as kidney damage or eGFR below 60 mL/min/1.73 m² for 3 or more months; staging guides treatment intensity and transplant eligibility discussions.
Creatinine
A waste product your muscles make constantly. Healthy kidneys filter it out; damaged kidneys let it pile up. A rising creatinine level is often the first sign that kidney function is declining.
Serum creatinine is used alongside age, sex, and race to calculate eGFR; it can be falsely elevated by high muscle mass or protein intake, so clinical context matters.
Dialysate
The special cleaning fluid used during hemodialysis. It flows on one side of a membrane while your blood flows on the other. Waste products move from the blood into the dialysate and are flushed away.
Dialysate composition — particularly potassium (1–4 mEq/L) and bicarbonate (35–40 mEq/L) — is individualized based on a patient's labs and acid-base status.
Dialysis
A treatment that does what your kidneys can no longer do — filter waste and extra fluid from your blood. Two main types: hemodialysis (using a machine and a filter) and peritoneal dialysis (using your belly lining as the filter).
Initiated when eGFR typically falls to 5–10 mL/min/1.73 m² or earlier if uremic symptoms, volume overload, or hyperkalemia are unmanageable.
Dry Weight
Your ideal body weight with no extra fluid — what you should weigh if your kidneys worked normally. During dialysis, the machine removes fluid until you reach your dry weight. Going below causes cramps; staying above causes swelling and heart strain.
Dry weight is reassessed regularly; clinical signs of over-hydration (edema, hypertension) or under-hydration (hypotension, cramps) guide monthly adjustments.
eGFREstimated Glomerular Filtration Rate
The most important number for measuring kidney function. It estimates how much blood your kidneys filter per minute. A score of 100 is normal; below 15 typically means kidney failure and the need for dialysis or a transplant.
Calculated from serum creatinine, age, and sex using the CKD-EPI 2021 equation; the five CKD stages are defined by eGFR thresholds: G1 (≥90), G2 (60–89), G3a (45–59), G3b (30–44), G4 (15–29), G5 (<15).
EPOErythropoietin
A hormone your kidneys normally make that signals bone marrow to produce red blood cells. CKD kidneys stop making enough EPO, which causes anemia. Dialysis patients often receive synthetic EPO as an injection.
ESAs (erythropoiesis-stimulating agents like epoetin alfa or darbepoetin) require adequate iron stores to be effective; KDIGO guidelines cite a typical target hemoglobin range of 10–11.5 g/dL to minimize cardiovascular risk — actual targets vary by patient and are set by your care team.
Fistula
Short for AV Fistula. See Arteriovenous (AV) Fistula above. A surgically created connection between an artery and vein that creates a strong access point for dialysis needles.
The fistula is preferred over grafts and catheters because it has the lowest complication rate and longest usable lifespan — often many years.
Fluid Overload
Too much fluid in the body because the kidneys cannot remove it. Signs include swollen ankles, shortness of breath, and weight gain between dialysis sessions. It strains your heart and lungs.
Chronic fluid overload is a major driver of left ventricular hypertrophy and heart failure in ESKD patients; interdialytic weight gain above 5% of dry weight significantly increases cardiovascular risk.
Fluid Restriction
A daily limit on how much you can drink (and eat, since many foods contain water). Dialysis patients typically restrict fluids to 32–48 oz per day because the machine removes only so much fluid per session safely.
Restriction is based on residual urine output plus estimated insensible losses; patients with no urine output (anuria) have the strictest limits, typically under 1 liter per day.
GFRGlomerular Filtration Rate
How well your kidneys filter blood — measured in milliliters per minute. The "e" in eGFR stands for "estimated" because it is calculated from a blood test rather than a direct measurement. The lower your GFR, the less your kidneys are working.
True measured GFR using inulin clearance is the gold standard but impractical clinically; eGFR is an accepted surrogate that tracks well with actual kidney function in most populations.
Graft (AV Graft)
A synthetic tube surgically implanted to connect an artery and a vein for dialysis access. Used when veins are too small or damaged to form a natural fistula. Ready to use in 2–3 weeks but needs more maintenance than a fistula.
Grafts have higher rates of clotting and infection compared to native fistulas and often require interventions such as angioplasty or thrombectomy to maintain patency.
HDHemodialysis
The most common type of dialysis in the US. Your blood travels through a tube into a machine that passes it through a filter (dialyzer), removes waste and extra fluid, and returns the clean blood to your body. Usually 3 times a week, 3–5 hours per session.
Conventional in-center HD provides about 12 hours of treatment per week; more frequent regimens (daily or nocturnal HD) improve outcomes but require home setup or extended-hours centers.
Hematocrit
The percentage of your blood that is made up of red blood cells. CKD patients often have a low hematocrit because damaged kidneys produce less EPO — resulting in anemia and fatigue.
Target hematocrit for dialysis patients on ESA therapy is approximately 33–36%; values are typically reported alongside hemoglobin on monthly lab panels.
Hemoglobin
The protein inside red blood cells that carries oxygen throughout your body. Low hemoglobin (anemia) in CKD means your organs are not getting enough oxygen — which causes fatigue, brain fog, and shortness of breath.
KDIGO guidelines recommend targeting hemoglobin of 10–11.5 g/dL with ESA therapy; higher targets increase cardiovascular risk without added benefit.
Hyperkalemia
Dangerously high potassium in the blood. Damaged kidneys cannot remove excess potassium, which can disrupt your heart's rhythm. This is one of the most life-threatening complications of kidney failure.
Potassium above 6.0 mEq/L requires urgent management; causes include dietary intake, acidosis, and missed dialysis sessions; EKG changes (peaked T-waves) appear at critically high levels.
Hyperphosphatemia
Too much phosphorus in the blood. Failing kidneys cannot remove phosphorus, so it builds up and pulls calcium from your bones — weakening them and depositing in blood vessels. Controlling phosphorus through diet and medication is critical.
Managed with dietary phosphorus restriction (<800–1000 mg/day), phosphate binders taken with meals, and adequate dialysis; KDIGO/K-DOQI guidelines cite a typical target serum phosphorus range of 3.5–5.5 mg/dL in dialysis patients — actual targets vary by patient and are set by your care team.
Hypotension (Intradialytic)
A sudden drop in blood pressure during a dialysis session. You may feel dizzy, nauseated, or faint. It happens when fluid is removed too fast or the session removes more than your body can handle at once.
Intradialytic hypotension (IDH) affects up to 25% of sessions and is defined as a systolic drop of ≥20 mmHg or absolute systolic below 90 mmHg; causes include excessive ultrafiltration rate or incorrect dry weight.
IDWGInterdialytic Weight Gain
The amount of weight you gain in fluid between two dialysis sessions. Too much gain means your heart and lungs must work overtime. Care teams commonly aim to keep interdialytic weight gain low — ask your care team what target is right for you.
IDWG above 4–5% of dry weight is associated with higher cardiovascular mortality; patients are coached to weigh daily and limit sodium and fluid to minimize interdialytic gains.
Iron Deficiency (CKD context)
Not having enough iron to make red blood cells. CKD patients commonly have iron deficiency due to blood loss during dialysis, poor absorption, and inflammation. Without enough iron, EPO injections will not work properly.
Assessed via serum ferritin and transferrin saturation (TSAT); IV iron is preferred for dialysis patients since oral absorption is poor; KDIGO guidelines cite a typical target range of ferritin 200–500 ng/mL and TSAT 20–30% — actual targets vary by patient and are set by your care team.
K/DOQI Guidelines
Evidence-based clinical practice guidelines published by the National Kidney Foundation. These are the "rulebook" that guides how doctors and dialysis centers care for kidney patients — from lab targets to access planning.
K/DOQI (Kidney Disease Outcomes Quality Initiative) was updated by KDIGO (global standards body); both are referenced by nephrologists and dialysis centers worldwide for treatment protocols.
Kidney Disease Stages (1–5)
CKD is divided into 5 stages based on how much kidney function remains (measured by eGFR). Stage 1 is mild damage with nearly normal function; Stage 5 is kidney failure (ESKD) requiring dialysis or transplant to survive.
Stages: G1 eGFR ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15; albuminuria category (A1–A3) is combined with G stage for full risk classification under KDIGO 2012.
Kt/VDialysis Adequacy
A score that tells you how effective each dialysis session was. K = how well the dialyzer clears urea, t = treatment time, V = body fluid volume. A score of 1.2 or higher means the session did its job adequately.
Measured monthly by comparing pre- and post-dialysis BUN; KDOQI recommends a minimum spKt/V of 1.4 per session to account for rebound; inadequate Kt/V is linked to higher hospitalization rates.
Metabolic Acidosis
When your blood becomes too acidic because damaged kidneys cannot remove acid or produce enough bicarbonate (a natural buffer). It causes fatigue, muscle wasting, and bone loss, and speeds up CKD progression.
KDIGO guidelines cite a typical target serum bicarbonate range of 22–26 mEq/L for CKD and dialysis patients — actual targets vary by patient and are set by your care team; treated with sodium bicarbonate supplementation in non-dialysis CKD or corrected via the dialysate bath in hemodialysis.
Nephrologist
A doctor who specializes in kidney diseases. They manage your CKD stage, prescribe dialysis, work with your transplant team, and adjust medications that affect your kidneys. Your most important specialist if you have CKD.
Board-certified nephrologists complete a 3-year fellowship after internal medicine residency; in the dialysis setting they perform monthly patient assessments and review labs, access, and adequacy.
Nephrology
The branch of medicine that specializes in kidney diseases. If your primary care doctor refers you to a "nephrologist," you are being sent to a kidney specialist who will manage your CKD, dialysis, or transplant evaluation.
Nephrology encompasses CKD management, electrolyte disorders, hypertension, glomerular diseases, dialysis modality selection, and kidney transplant coordination.
Parathyroid HormonePTH
A hormone that regulates calcium and phosphorus in your body. In CKD, PTH levels rise dramatically as the body tries to compensate for low calcium. Chronically elevated PTH weakens bones and causes the condition called renal osteodystrophy.
Intact PTH target for dialysis patients per KDIGO is 2–9 times the upper normal limit (approximately 150–600 pg/mL); managed with active vitamin D, calcimimetics, and phosphate control.
PDPeritoneal Dialysis
A type of dialysis done at home using the lining of your own belly (peritoneum) as a natural filter. A catheter is placed in your abdomen, dialysate fluid is pumped in and out, and waste moves across the lining into the fluid which drains away.
PD can be done manually (CAPD) or with an automated cycler overnight (APD); it preserves residual kidney function longer than HD and offers schedule flexibility, but requires daily commitment and technique discipline.
Phosphorus
A mineral found in most proteins and processed foods. Healthy kidneys excrete excess phosphorus; failing kidneys cannot. Too much phosphorus weakens bones, hardens blood vessels, and causes itchy skin.
High-phosphorus foods include dairy, nuts, dark colas, and processed meats; phosphate binders (calcium-based or non-calcium-based) are prescribed to be taken with every meal and snack.
Potassium
An electrolyte your body needs for muscle and nerve function — especially your heart. CKD patients must limit potassium because damaged kidneys cannot remove the excess, which can cause a dangerous and potentially fatal heart rhythm problem.
Dialysis patients typically restrict potassium to 2,000–3,000 mg/day; high-potassium foods include bananas, tomatoes, potatoes, and oranges; leaching vegetables can reduce content by 30–50%.
Renal Diet
A specific eating plan for people with kidney disease. It limits potassium, phosphorus, sodium, and sometimes protein and fluid — depending on your CKD stage. What you eat directly affects your lab values and how you feel.
Dietary recommendations change across CKD stages; a registered renal dietitian (RD specializing in CKD) provides individualized guidance based on monthly lab results and treatment modality.
Renal Osteodystrophy
Bone disease that develops when kidney failure disrupts calcium, phosphorus, and PTH balance. Bones become weak, brittle, and painful. It can also cause calcium to deposit in arteries, raising heart attack risk.
Also called CKD-MBD (mineral and bone disorder); managed through a triad of phosphate control, vitamin D therapy, and PTH suppression with calcimimetics like cinacalcet.
Sodium
Salt. Sodium makes your body hold onto water, which raises blood pressure and causes swelling. CKD patients are typically advised to limit sodium to 1,500–2,000 mg per day. Low sodium also helps you stay within your fluid limit.
Every 1 gram of sodium consumed retains approximately 250 mL of water; reducing dietary sodium lowers both IDWG and blood pressure burden in dialysis patients.
Stage 5 CKD (ESKD)
The final stage of chronic kidney disease, also called End-Stage Kidney Disease (ESKD) or kidney failure. Your kidneys are working at less than 15% of normal capacity. Dialysis or a kidney transplant is necessary to stay alive.
ESKD management options are hemodialysis, peritoneal dialysis, preemptive kidney transplant, or conservative (palliative) management; transplant is the preferred treatment for eligible patients due to better survival and quality of life.
Symptom Management
The ongoing effort to treat the side effects of kidney disease and dialysis — including fatigue, itching, nausea, cramps, restless legs, and sleep problems. Managing symptoms is as important as managing lab values.
Symptom burden in ESKD is high and often underreported; validated tools like the Kidney Symptom Index (KSI) and ESAS-r assist clinicians in tracking and addressing patient-reported symptoms systematically.
Transplant Waitlist
The national registry managed by UNOS where kidney patients are listed when they qualify for a transplant. You stay on dialysis while waiting. Time on the list, blood type, and location affect how long the wait is.
Patients accrue waiting time from the date of listing (or earlier if they had prior dialysis); the average wait for a deceased-donor kidney varies by blood type and region, ranging from 3 to 10+ years; living donors significantly shorten wait times.
Tunneled Catheter
A longer-term dialysis catheter placed under the skin of the chest, with the tip sitting in a large vein near the heart. Unlike a temporary catheter, it is designed to stay in for weeks to months while a fistula or graft matures.
The cuff on a tunneled catheter anchors it in the subcutaneous tissue and reduces infection risk compared to uncuffed temporary catheters; exit-site care with antiseptic dressings is required at each session.
Uremia
When your blood fills up with waste products (like urea) that the kidneys should be removing. Symptoms include nausea, vomiting, brain fog, itching, and loss of appetite. Uremia is what happens when dialysis is delayed or insufficient.
Uremic syndrome encompasses both the buildup of identified solutes and less well-characterized "uremic toxins"; it is the primary indication for initiating renal replacement therapy when eGFR falls below 10 mL/min/1.73 m².
Urine Output (Anuria)
How much urine your kidneys still produce. As CKD progresses, urine output decreases. Anuria means making less than 100 mL of urine per day — essentially none. At this point, dialysis must remove all excess fluid.
Preserving residual renal function (RRF) even in dialysis patients is associated with better survival and quality of life; nephrotoxic drugs (NSAIDs, aminoglycosides) should be avoided to protect remaining function.
Vascular Access
The point on your body where dialysis machines connect to your blood. There are three types: fistula (best), graft (second choice), and catheter (last resort). Good vascular access is essential for effective dialysis and your long-term health.
The "Fistula First, Catheter Last" initiative has increased fistula prevalence to over 65% in US HD patients; vascular access problems (clotting, infection) remain the leading cause of hospitalization in the ESKD population.