IgAN Glossary

The Foundation for IgA Nephropathy

IgAN Glossary

This section is not yet complete, but is being added to regularly. Thank you for your patience. Many common terms and abbreviations can already be found below. Please note that the glossary definitions are intended for IgAN patients.

Additionally, an excellent kidney disease glossary is available on the website of the Royal Infirmary of Edinburgh Renal Unit (in the U.K.). Go to Kidney Diseases and Words.

Common abbreviations you may encounter:

BX - biopsy

DX - diagnosis

TX - transplant

K - potassium

Na - sodium

s cr - serum creatinine

cr cl - creatinine clearance

BUN - blood urea nitrogen

Common biopsy report and renal disease terms:

Creatinine clearance: Creatinine is a natural by-product of muscle function. When muscles are used, they produce creatinine which enters your bloodstream. Creatinine just happens to be freely-filtered by the kidneys and not reabsorbed by them. Because of this, it can be used to estimate kidney function. The less kidney function a person has, the more creatinine builds up to higher levels in the blood. After a patient collects all urine for 24 hours, the lab measures and compares the amount of creatinine in your urine collection with the amount of creatinine in your blood sample which is drawn after the 24 hours when you bring the urine container into the lab. Creatinine clearance is roughly equal to glomerular filtration rate, and so, with this number, kidney function can be estimated pretty accurately. Your nephrologist interprets this appropriately, because, a certain amount of creatinine is eliminated by the renal tubules rather than filtered by the glomeruli, and so this can throw off the number somewhat, especially as GFR gets closer to 20%.

Crescents: A moon-shaped fibrous tissue proliferation in the glomerulus which fills all or part of Bowman's space. Crescents indicate severe damage to the glomerular basement membrane, and the presence of crescents is often an ominous risk factor for quick progression to end-stage renal disease.

Diffuse: All or most (greater than 75-80%) of the glomeruli in a tissue section are diseased. It's the opposite of focal. IgAN can be focal or diffuse.

Echogenicity: This term is often found in the report from a kidney ultrasound, usually stated as "increased cortical echogenicity". This finding results from the replacement of irreversibly damaged nephrons with fibrous scar tissue. To assess the amount of damage, it is necessary to order a kidney biopsy.

End-stage renal disease (esrd): Whatever kidney disease got the person there, this is what it is called when the person finally no longer has enough kidney function left to stay alive without permanent renal replacement therapy (dialysis or kidney transplant). More about esrd is explained elsewhere on this website.

Fibrosis: Dense type I collagen deposited in the glomeruli and/or interstitium and/or blood vessels.

Fistula: An arterio-veinous, or AV fistula is a surgical connection between an artery and a vein, usually in the upper or lower non-dominant arm. After the surgery, the vein so-connected enlarges due to being under a higher pressure than veins normally are. It takes at least a few weeks, and more usually a few months for the fistula vein to "mature" or enlarge enough for use. Once ready, the fistula can be used as the needling site for hemodialysis. This is considered the best type of long-term access for hemodialysis. Because of the time needed for maturing before it can be used, surgery to emplace an AV fistula should ideally be done approximately 6 months to a year before the time dialysis is expected to be needed. Health professionals frequently refer to a fistula as a shunt, presumably because the first practical dialysis access was in fact called a shunt. A fistula uses absolutely nothing artificial. It is simply a vein near the surface that is connected to an artery (arteries are much deeper than veins). A dialysis access roughly similar to an AV fistula is a graft. A graft is usually a piece of gortex "tubing" which serves the same purpose as a fistula vein. It is used in people who do not have veins adequate for an AV fistula.

Flare-up: In the context of IgA nephropathy, the term "flare-up" is used by patients and nephrologists alike to mean an episode when the disease suddenly becomes more active in the form of micro-hematuria (microscopic blood in the urine) or no hematuria which suddenly becomes macro-hematuria (visible blood in the urine). It may or may not be accompanied by a jump in proteinuria. A flare-up is a temporary, usually self-limiting condition. It often happens at the same time the patient has an upper respiratory infection, and it has been reported with abdominal infections. The sudden appearance of blood in the urine, which makes the urine tea or cola-colored, can be frightening, but it is usually not a serious event. While heavy proteinuria can be treated, there is no specific treatment for a flare-up of macro-hematuria. It usually resolves on its own as the upper respiratory infection which provoked it resolves. Sometimes, a flare-up may seem to happen for no particular reason. A flare-up does not represent a loss of kidney function and, as dramatic as it seems, it is rarely a problem by itself. As already stated, a flare-up of macro-hematuria usually makes the urine look like tea or cola. Red urine usually signifies that the blood is coming from somewhere else in the urinary tract.

Focal: Some glomeruli in a section are diseased (less than 75-80%). It's the opposite of diffuse. IgAN can be focal or diffuse.

Focal Segmental Glomerulosclerosis: portions of many glomeruli are destroyed. Focal Segmental Glomerulosclerosis (FSGS) may be a disease on its own, or it may simply be a physical description of what is seen in the biopsy sample. Some IgA nephropathy patients may see this term in their biopsy report.

Global: This is when the process affects the entire glomerulus, not just parts of it. Global diseases are usually also diffuse. Global is the opposite of segmental. More simply stated, global means that if a glomerulus is involved, all portions of it are involved.

Glomerular filtration rate (GFR): This is the rate at which your kidneys filter. Basically, it is what we patients refer to as "kidney function". GFR is estimated using a mathematical formula (of which there are a number, but a common one is the MDRD formula). For example, if a GFR formula or calculator gives you a result of 10 ml/min/1.73 m2 , this means you have about 10% kidney function, and it's time to start you on dialysis. GFR can also be estimated by using creatinine clearance from a 24 hour urine collection. For more information, see GFR in the Tests section.

Glomerulonecrosis: Injury to the nephrons characterized by small and shrunken glomeruli with collapse of capillary loops which do not receive enough blood flow (due to hypertrophy of the smooth muscle layer and narrowing of the lumen in preglomerular arterioles). This kind of damage is often caused by hypertension (hypertension by itself can lead to kidney failure, and as many of us with IgAN know, IgAN can cause significant hypertension). Slightly different than glomerulosclerosis, which is caused by a proliferative disease process such as IgAN, where proliferation of cells fills in and leads to collapse or blockage of the capillary loops. Don't worry too much about the technical terminology. I'm not a renal pathologist, but the differences seem pretty subtle to me, as hypertension can also lead to glomerulosclerosis. The end result is the same: non-functional glomeruli and therefore loss of kidney function.

Glomerulonephritis: As this term is commonly used, this means that the glomeruli are inflamed enough to cause at least some of them to lose blood into the renal tubule and then into the urine.

Glomerulosclerosis: "Scarring" of a glomerulus due to any chronic disease process. Scarring means that the lumen (ie. the inside open part of the little blood vessels in the glomeruli) are blocked or squeezed shut due to increase of the basement membrane and/or expansion of the mesangial matrix. Such scarring usually represents permanent, irreversible damage to the glomeruli.

Hyaline casts: People will often see they have this on their urinalysis report. It's meaningless. Everybody has hyaline casts.

Interstitial nephritis: Inflammation of the kidney which affects the interstitial spaces but not the glomeruli. Of course, the glomeruli may be affected separately by whatever kidney disease is present.

MDRD formula: This is short for the Modification of Diet in Renal Disease study. It's of interest to kidney patients mainly as the MDRD formula for calculating GFR (see glomerular filtration rate). There are a number of equations or formulae available for estimating GFR, but the MDRD one is the most recent ones, and it has been proposed as the standard by which nephrologists should estimate kidney function. It's a very accurate formula, but don't bother using it if you have close to 100% kidney function or very mild IgAN, because the formula is known to significantly underestimate kidney function in healthy persons and people with kidney disease who have preserved kidney function (no use scaring yourself for no reason). It may also NOT be as accurate in the elderly and in African-Americans, as these groups were under-represented in the study. The MDRD formula should not be used for pediatric cases. You can find an MDRD GFR calculator at nephron.com. Always consult with your nephrologist about kidney function. Do not interpret on your own, as any formula may be inaccurate by up to 30%.

Membrano-proliferative: see membranous and proliferative.

Membranous: A process which affects mainly the glomerular basement membrane of the glomeruli. Membranoproliferative means membranous thickening and cellular proliferation.

Mesangial: Pertaining to the mesangium, which is a part of the glomerulus. IgAN is usually a mesangial proliferative disease. Other mesangial pattern diseases are IgM mesangial proliferative nephropathy, membranoproliferative glomerulonephritis type I, and lupus nephritis.

Mesangio-proliferative: see mesangial and proliferative.

Nephritic vs nephrotic: basically, nephritic means inflammation causing blood leaking into the urine, and nephrotic means inflammation causing protein leakage into the urine. Of course, a person with kidney disease could be both nephritic and nephrotic. IgAN is really more of a nephritic disease, but it's also nephrotic in the sense that one symptom is proteinuria. Proteinuria is usually mild or moderate, but it can in some cases be heavy.

Nephritis: Used by itself, this is simply short for "glomerulonephritis".

Nephropathy: Anything wrong with the kidney - glomeruli, tubules, or vessels. The word glomerulopathy is also often used to mean a nephropathy which affects primarily the glomeruli.

Nephrotic range proteinuria: This is a term people who have heavy proteinuria may encounter. All it means is that the proteinuria is in the range where symptoms of nephrotic syndrome are expected to start developing. It is generally-accepted to mean proteinuria which is greater than 3.5 grams per day.

Nephrotic syndrome: This describes a group of symptoms that eventually develop when there is heavy proteinuria (protein leakage at the glomerular capillaries and eventually into the urine). This usually indicates acute inflammation of the glomeruli. Heavy proteinuria is usually defined as greater than 3.5 grams per day of protein in the urine, but some people my start showing symptoms of nephrotic syndrome earlier, or later. The symptoms are mainly swelling of tissues everywhere (abdomen is common), high cholesterol, low level of protein in the blood. A person can sometimes be diagnosed with nephrotic syndrome as the primary disease, if no other cause can be found. People with nephrotic syndrome may be more susceptible to infections.

Proliferative: More cells than normal in the glomerulus. In the case of IgAN, it's usually mesangial proliferation, which is a proliferation of the cells in the mesangium of the glomeruli (hence, IgAN is one of the mesangio-proliferative kidney diseases).

Red blood cell casts: These are characteristic clumps of red blood cells found in the urine that have been formed into the shape of casts more or less the shape of the renal tubules (small cylinders of red blood cells). Red blood cells in the form of casts are not always present in the urine of people with kidney disease who have blood in their urine, but when they are, it is almost always a sign of some kind of kidney disease, since the blood must have come through the renal tubules to be shaped like this.

Segmental: Only some parts of an individual glomerulus are affected. Segmental diseases are usually also focal. Segmental is the opposite of global.

Waxy casts: These large casts are a sign of kidney disease. They are caused by a low flow through the renal tubules.

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