Kidney Test Glossary

• A
• C
• D
• E
• G
• H
• K
• M
• N
• O
• P
• R
• S
• T
• U

A

ACR (albumin-to-creatinine ratio)

A urine test that compares the amount of albumin (a protein) with the amount of creatinine in the same sample. It is usually done on a single urine sample, ideally the first one of the morning. Labs report it in mg/mmol or mg/g. KDIGO groups results as A1 (below 3 mg/mmol, or below 30 mg/g), A2 (3 to 30 mg/mmol, or 30 to 300 mg/g) and A3 (above 30 mg/mmol, or above 300 mg/g). A raised result is usually repeated to confirm it. See urine ACR.

Acute kidney injury (AKI)

A sudden drop in kidney function over hours or days, for example during a severe illness or dehydration. It needs prompt medical assessment. It is different from chronic kidney disease, which is long term.

Albumin

The main protein in the blood. Healthy kidneys keep almost all of it in the blood and out of the urine.

Albuminuria

Albumin in the urine. It can be an early sign that the kidney's filters are damaged. It is measured with a urine ACR test. Doctors look at albuminuria and eGFR together to assess the kidneys.

C

Chronic kidney disease (CKD)

Kidney damage or reduced kidney function that has been present for more than 3 months. It is assessed using eGFR (from a blood test) and urine ACR together, and followed over time. See chronic kidney disease.

CKD stage

A way of describing CKD using two categories. The G category comes from eGFR: G1 (90 or above), G2 (60 to 89), G3a (45 to 59), G3b (30 to 44), G4 (15 to 29) and G5 (below 15), all in mL/min/1.73m². The A category comes from urine ACR: A1, A2 or A3. A person might be described as G3a A2, for example. See CKD stages.

Creatinine

A waste product made by the muscles and removed from the blood by the kidneys. The blood level depends on how well the kidneys filter, but also on muscle mass, age, sex, diet and some medicines. On its own it does not diagnose kidney disease. It is used to calculate eGFR. Reference ranges vary by lab, so use the range printed on your report. See creatinine test.

Cystatin C

A protein in the blood that can also be used to estimate kidney function. It is less affected by muscle mass than creatinine. Guidelines suggest using it together with creatinine when a more accurate estimate is needed.

D

Dialysis

A treatment that takes over some of the kidneys' filtering work when the kidneys have failed. In haemodialysis, blood is cleaned by a machine, usually at a dialysis unit several times a week. In peritoneal dialysis, fluid is placed in the abdomen through a small tube and the lining of the abdomen acts as the filter. Decisions about dialysis are made with a kidney specialist.

E

eGFR (estimated glomerular filtration rate)

An estimate of how well the kidneys are filtering the blood. It is calculated from your creatinine result (and sometimes cystatin C), your age and your sex, using a validated equation. It is reported in mL/min/1.73m². A lower number means the kidneys are filtering less. See eGFR.

Electrolytes

Minerals in the blood that carry an electrical charge, such as sodium, potassium, chloride and bicarbonate. The kidneys help keep them at the right levels.

G

GFR (glomerular filtration rate)

The amount of blood the kidneys filter each minute. Measuring it directly is complicated, so in everyday care it is estimated as eGFR.

Glomerulus

A tiny filter inside the kidney. Each nephron has one. The plural is glomeruli.

H

Haematuria

Blood in the urine. It may be visible, or seen only on a urine test. It has many possible causes, including infection, stones and conditions of the kidney or bladder, so it should be checked by a doctor.

Hypertension

High blood pressure. Many people call it presha. Over time it can damage the kidneys, and kidney disease can also raise blood pressure. See blood pressure and kidneys.

K

Kidney function tests

A group of blood tests, often creatinine, urea and electrolytes, requested together to check the kidneys. On request forms and reports in Kenya you may see them written as UECs (urea, electrolytes and creatinine). See kidney function tests.

Kidney ultrasound

A painless scan that uses sound waves to show the size and shape of the kidneys, and to look for blockage, cysts or stones. It does not use radiation. See kidney ultrasound.

M

mL/min/1.73m²

The unit used for eGFR. It means millilitres of blood filtered per minute, adjusted to a standard body size so that results can be compared between people.

N

Nephrologist

A doctor who specialises in kidney disease. Nephrologists look after chronic kidney disease, kidney function that is falling, protein or blood in the urine that needs investigation, dialysis and kidney transplant care. See what a nephrologist does.

Nephron

The basic working unit of the kidney. Each kidney contains a very large number of nephrons. Each one has a filter (the glomerulus) and a small tube that adjusts the fluid before it becomes urine.

Nephropathy

A general word for kidney disease. For example, kidney disease caused by diabetes is sometimes called diabetic nephropathy.

O

Oedema

Swelling caused by fluid building up in the body, often in the feet, ankles, legs or around the eyes. It has many causes, including heart, liver and kidney problems. See swollen feet.

P

PCR (protein-to-creatinine ratio)

A urine test similar to ACR, but it measures all types of protein, not only albumin.

Potassium

An electrolyte that nerves, muscles and the heart need to work properly. The kidneys remove extra potassium from the body. Levels that are too high or too low can affect the heart rhythm, so doctors watch potassium closely in people with kidney disease.

Proteinuria

Protein in the urine. Albumin is the protein most often measured. A urine dipstick can detect protein, and a urine ACR or PCR test measures how much. See protein in urine.

R

Reference range

The range a lab uses to compare your result with. It varies between labs and testing methods, and for some tests by age and sex. Always use the range printed on your own report.

Renal

Relating to the kidneys. For example, a renal ultrasound is a kidney scan, and a renal unit is a kidney care department.

S

Sodium

An electrolyte that helps control the balance of water in the body. The kidneys help keep sodium at the right level.

T

Transplant (kidney)

An operation to place a healthy kidney from a donor into a person whose own kidneys have failed. It is one of the treatment options a kidney specialist may discuss when kidney function is very low.

U

Urea

A waste product made when the body breaks down protein. It is removed by the kidneys. Urea levels are also affected by how much you drink, what you eat and some illnesses, so doctors read it alongside creatinine and eGFR. In some countries it is reported as blood urea nitrogen (BUN).

Urinalysis

A test of a urine sample. A dipstick checks for things such as protein, blood, sugar and signs of infection, and the sample may also be looked at under a microscope. See urinalysis.

Urine dipstick

A strip of card with small test pads that change colour when dipped in urine. It gives a quick check for protein, blood, sugar and infection. Abnormal results are usually followed up with more precise tests.

Urologist

A surgeon who specialises in the structure of the urinary tract, including the kidneys, bladder and prostate. Urologists treat problems such as kidney stones, blockages and tumours. See nephrologist or urologist.

Sources

1. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. kdigo.org
2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Kidney disease. niddk.nih.gov
3. National Kidney Foundation. kidney.org
4. NICE guideline NG203: Chronic kidney disease: assessment and management. nice.org.uk

This page explains kidney tests and terms in general. It is not a diagnosis and does not replace advice from a doctor who knows your history. Your results should be interpreted together with your symptoms, other tests and a clinical assessment. Medical disclaimer.