Rare Renal Glossary


Acute Kidney Injury (AKI) - a sudden reduction in kidney function. AKI can occur due to stress on the kidneys as a result of illnesses or infection. It might be due to severe dehydration or it could be the result of the side effects of some drugs. Sometimes it’s due to a combination of factors. Acute kidney injury can get better in a few days or weeks, but sometimes it causes ongoing problems. Although called acute kidney injury it is not caused as a result of a physical blow to the body. Nor is it caused by excessive intake of alcohol, yet it should be remembered that too much alcohol can damage your other organs, and cause you to be dehydrated.


Amino Acid - Many amino acids occur in nature. Only 22 are used as the building blocks of proteins. Nine of these are "essential" amino acids, meaning that we need to get them from our food as we cannot make them ourselves. They link to each other to create chains of amino acids (peptides) that are folded or joined to other peptides to make proteins.

The body's ability to line up amino acids in the right order to make a protein is governed by genes, and the process of making a peptide from a gene is called translation. This is why a fault in a gene can lead to the production of a faulty protein. This in turn gives rise to a structural or functional change in the body, sometimes a disease.

Some amino acids are not used in protein production but have biological effects of their own. This includes transmitting messages between nerve cells, for example.

An amino acid is defined by its make up with an amine (-NH2) and a carboxylic acid (-COOH) structure linked to a carbon side chain.


Amniotic fluid - Fluid that surrounds an unborn baby during pregnancy. It contains protein and carbohydrates which help the baby to grow. The fluid allows the baby to move about in the womb and protects it from injury by cushioning sudden movements. The amount of fluid in the womb increases as the baby grows. A lack of amniotic fluid can cause breathing difficulties when the baby is born as the lungs are not fully developed.


Anaemia - A shortage of red blood cells. Anaemia can result in reduced energy, breathlessness and a feeling of weakness. Iron tablets are often used as treatment.


Angiotensin Converting Enzyme (ACE) inhibitor - A medication originally designed to reduce blood pressure. ACE inhibitors also reduce the scarring process in the glomeruli, slowing the progression of kidney disease. It is normally prescribed as a pill to be taken once a day. Brand names include Ramipril and Enalapril. A blood test is usually performed before starting treatment to record the level of kidney function. Side effects of the treatment are uncommon but may include persistent irritating cough.


Angiotensin Receptor Blocker (ARB) - Similar to ACE inhibitors, this is another form of medication designed to reduce blood pressure. It is often prescribed if ACE inhibitors have caused side effects such as a persistent cough. Brand names often end in -sartan such as Losartan and Irbesartan. As with ACE inhibitors a blood test is usually performed before starting treatment. ARB medication is used like ACE inhibitors to slow the progression of certain types of kidney disease.


Audiogram - A test to measure the range of an individual’s hearing. Sounds are presented through a set of headphones and the individual is required to indicate when they hear a sound. Usually they are asked to press a button the moment they hear the sound. The sounds vary in volume and frequency (high pitch to low pitch) to represent the full range of human hearing.


Bile - A greenish-brown liquid produced by the liver. It transports waste products from the liver and aids digestion by breaking down fats in the small intestine.


Bile ducts - Tiny tubes used to transport bile from the liver.


Chromosome - Thread-like structures found in the cell. Chromosomes contain genetic information in the form of genes which control all activity in the body. Each human cell will normally contain 46 chromosomes grouped into 23 pairs. 22 of these pairs are the same in both sexes. The remaining pair are the sex chromosomes. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). One X chromosome comes from the mother’s egg while the other chromosome (X for females; Y for males) comes from the father’s sperm.


Chronic Kidney Disease (CKD) - a common long-term condition, usually affecting the older generation. A diagnosis of CKD means your kidneys are not working as effectively as they used to. The older you are the more likely you will have a degree of CKD.


Collagen fibres - Strong proteins found in bones and connective tissue. Collagen is very tough and helps support the structure of the body’s organs.


Cysts - Fluid-filled sacs that can vary in size and may occur anywhere in the body. Often they do not cause any problems and can be left untreated. Problems can develop if the cysts grow very large or when multiple cysts develop in the same organ such as the kidneys, stopping them from working properly.


Dialysis - When the kidneys stop working properly, machines are used to take over some of their function. There are two different kinds of dialysis, both widely used in the UK - haemodialysis and peritoneal dialysis. Both systems control the amount of water and salt in the body and help to remove some of the waste products that our bodies produce. Dialysis can take over the function of the kidneys but does not make them better. It is usually used while a patient is waiting for a transplant.


Enzymes - Substances which cause chemical changes to take place in the body.


Erythropoietin (EPO) - a hormone that is made mostly in the kidneys. The cells that make it are found in the lining of the capillary blood vessels. These capillaries form a network around the renal tubules in the cortex (outer part) of the kidney. EPO is released into the blood stream and is picked up by the developing red blood cells (red corpuscles). These immature  red cells produce a receptor for EPO at a specific stage in their maturation. Once EPO binds onto  the receptor, the next stage of red cell development can continue. Without this step, red cell production stops. This way EPO controls the production of red cells and therefore the red cell composition of blood.

Red blood cells carry oxygen from the lungs to the rest of the body. The cortex of the kidneys receives a very high flow of oxygenated blood. Therefore it makes sense that the kidney has a central role in 'sensing' oxygen delivery and regulating red cell production accordingly.

In chronic kidney disease the ability of the kidneys to produce EPO falls, and this leads to anaemia.


Erythropoiesis Stimulating Agents (ESA) - synthetic molecules that mimic the way EPO stimulates the production of red cells. They have been available as treatment to replace natural EPO and correct anaemia the since the 1980s.


Glomerular Basement Membrane - A mesh of proteins which forms the boundary between the blood and urine. Water and other small molecules are filtered across this membrane from the blood to pass out of the body in the urine.


Glomerular filtration rate (GFR) - A measure of how fast the kidneys are cleaning the blood. Measured in millilitres per minute, a healthy kidney will have a GFR of 90 ml/min or more.


Glomeruli (plural) Glomerulus (singular) - Tiny filters found in the outer part of the kidneys which are responsible for filtering the blood stream. Glomeruli are actually tiny arteries folded up into a ball, and tucked inside a capsule which collects the filtered fluid. These microscopic blood vessels are thin walled and very permeable to water and small molecules. They are commonly known as glomerular capillaries. Each capillary is a tiny tube with blood flowing inside it. The wall of the tube has a perforated lining like a colander. This is surrounded by a strong membrane called the Glomerular Basement Membrane.


Glyoxylate - A chemical produced in the liver which controls the production of oxalate inside the body.


Gout - Gout is a form of arthritis, where the inflammation in the joint is caused by excess uric acid. Uric acid is a normal waste product of metabolism. At abnormally high concentrations, uric acid tends to get deposited in certain parts of the body as microscopic crystals. These cause local inflammation, redness, swelling and pain. In gout, certain joints are particularly likely to be affected such as the fingers and toes.

Gout is a common condition and affects men more than women, and the elderly more than the young. The predisposing factors for the development of gout are genetic, with a small contribution related to diet. There are rare genetic conditions that cause excess uric acid, gout and kidney disease.


Haemodialysis - A way of treating the blood by passing it through an artificial filtering system. A small tube called a fistula is inserted in the arm, usually under a local anaesthetic. This is then connected to the dialysis machine so that the blood can be pumped through the filter and cleaned before being returned to the body. Most patients require at least three sessions of haemodialysis a week, with each session lasting around four hours. Treatment usually takes place in hospital but can be set-up at home.


Kidney Biopsy - A small sample of kidney tissue is taken from the body for microscopic examination to provide a diagnosis.

This is a routine medical test for a wide number of kidney conditions. It is usually done using local anaesthetic, although in younger children sedation or general anaesthesia is often preferred. Mostly is can be done as a day case. The sample is taken through a tubular needle, slightly bigger than the kind of needle used for a blood test. Inside the needle is a retractable blade. Using an imaging technique, usually an ultrasound scan, the doctor steers the needle through the back muscles to the position of one of the kidneys. The blade is activated and a thin core of the kidney is captured and held inside the tubular needle. The needle is then withdrawn and the sample processed for microscopic examination.


Kidney Stones - Hard masses of chemicals that can form in the kidney or bladder. They can range in size from microscopic crystals to the size of potatoes. Stones are formed when chemicals that are normally transported out of the body in the urine are left behind and build-up to form solid crystals. Some stones do not cause any symptoms at all while others result in extreme stomach pain, nausea and difficulty passing urine.


Nephrotic Syndrome - the key feature of nephrotic syndrome is that extra fluid is retained in the body and causes swelling. This is usually first noticed as swollen eyelids or a puffy face that is worse first thing in the morning. Later in the day, after being upright, the fluid collects in the legs and appears as swollen ankles. The swelling is soft and if you press on it for a moment you leave a dent. After a few minutes the dent fills back in. The term for this swelling is oedema. Sometimes the extra fluid collects in the abdomen and patients feel distended. This is called ascites.

Nephrotic syndrome is not a diagnosis in itself. There are several kidney conditions that can cause it.  However, it is important to recognise it because it describes the way in which fluid is retained. That is often an important clue as to what is happening in the kidneys.

In brief, the watery fluid of the blood stream (plasma), is rich in proteins, especially albumin. If you know that an egg white is chicken albumin dissolved in water, you get the picture of plasma containing human albumin. When the kidneys filter the plasma they normal keep the albumin and other proteins  and don’t let them cross over into the urine. In nephrotic syndrome this fails to happen so albumin pours into the urine and is lost.  The body tries to make more albumin and other proteins but it is never enough, and the level of albumin in the blood falls.

Albumin in the blood stream is important in drawing fluid from the tissues back into the circulating blood. Without the albumin more water moves out into the tissues of the body than gets returned. Because of this, extra fluid builds up in the tissues. Soft tissues like the fat layer under our skin has the most room to expand and that is why the swelling is more obvious in certain places.

The kidneys control the amount of water in the body. The loss of albumin cause them to re-set where they "think" the right amount of fluid should be. They retain more than is normal. This adds to the problem.

Nephrotic syndrome is easily recognised by clinicians. A simple bed-side stick test of the urine will show huge amounts of protein.  A blood test will confirm that the level of albumin in plasma is low.

The medical significance of this is that the problem can be pin-pointed to the filters of the kidney, the glomeruli.


Oxalate - A salt-like chemical formed by the breakdown of proteins and vitamin C during digestion. Its production is controlled by enzymes found in the liver. Oxalate is normally absorbed into the small intestine and leaves the body in the urine. If too much oxalate is allowed to build-up inside the body it can combine with calcium to form kidney stones.


Peritoneal dialysis - A way of treating the blood inside the body by passing dialysis fluid into the abdomen through a catheter and removing the waste products. The catheter is inserted under a general anaesthetic and dialysis must take place daily in order to be effective. This can take place at home either automatically during the night or manually four times a day following training.


Photophobia - discomfort of the eyes in bright light.


Proteins - Substances produced by the body which control how cells and organs work. They are the main building material for muscles, blood, skin and organs.


Renal colic - Pain when passing a kidney stone. The pain starts in the back or side of the tummy and moves down towards the groin area. It may last for minutes or hours, with intervals in between when there is no pain. Sometimes it is associated with nausea (feeling sick), and there may also be blood in the urine, although this is not often visible to the naked eye. The blood in the urine is usually caused by the stone scratching the ureter, part of the urinary tract.


Slit Lamp - a thin strip of light shone into the eye.


Stages of chronic kidney disease - Kidney disease is described in stages based on how quickly the kidneys are cleaning the blood. This is known as the glomerular filtration rate (GFR) and is measured in millilitres per minute. The five stages of kidney disease are detailed in the table below along with their associated GFR level.

Stage of Chronic Kidney Disease


GFR Level


Kidney function remains normal but urine findings suggest kidney disease

90 ml/min or more


Slightly reduced kidney function with urine findings suggesting kidney disease

60 to 89 ml/min


Moderately reduced kidney function

30 to 59 ml/min


Severely reduced kidney function

15 to 29 ml/min


Very severe or end-stage kidney failure

Less than 15 ml/min or on dialysis


Systemic Oxalosis - A build-up of oxalate following kidney failure.


Syndrome - Certain patterns of illness that tend to occur together. Doctors have to recognise these patterns in order make a diagnosis. A syndrome may therefore be the equivalent of a diagnosis. However, modern medicine demands increasing detail and accuracy in the definition of a disease. Relying on a syndrome description may not be enough. A particular syndrome may have different causes, and require different treatments. Patients given a diagnosis of a "syndrome" should ask their doctor whether this gives the best definition and detail of their illness.


Transplant - Replacing a damaged organ with a new, healthy one. Most transplants come from people who have died in hospital on life support machines. They can also come from living people like a close relative or friend. Transplanted organs are carefully chosen to give the best possible change of success. It can take months or even years for a right match to become available.


Tubules - Miniature tubes inside the kidneys. They are connected to the glomeruli, the kidney's filtering system, and receive the watery fluid coming out of the filter. The tubules reabsorb water and salt back into the bloodstream. Any fluid left over at the end is urine. The tubules can selectively excrete watse products into the urine or recover valuable compounds back into the body. Each glomerulus has its own tubule and together these are called a nephron.


Urinary Tract - the kidney’s drainage system. It is made up of the kidneys, ureters, bladder and urethra. The ureters are narrow muscular tubes which connect the kidney to the bladder. The bladder stores urine until you are ready to go to the toilet, and the urethra is a pipe through which the urine passes out of the body.


Uric Acid - A chemical compound found in the blood. It is created when the body breaks down substances found in certain types of food and drink, including meat, eggs, alcohol and caffeine. Uric acid normally dissolves in the blood and leaves the body in the urine. When too much uric acid is produced for the body to process, gout may develop.


Glossary version 3 updated August 2016

Written by the Rarerenal.org operational management board



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