Glomerulonephritis (GN) is a term used to refer to several kidney diseases (usually affecting both kidneys). Many of the diseases are characterised by inflammation either of the glomeruli or of the small blood vessels in the kidneys, hence the name, but not all diseases necessarily have an inflammatory component. As it is not strictly a single disease, its presentation depends on the specific disease entity: it may present with isolated hematuria and/or proteinuria (blood or protein in the urine); or as a nephrotic syndrome, a nephritic syndrome, acute kidney injury, or chronic kidney disease. They are categorized into several different pathological patterns, which are broadly grouped into non-proliferative or proliferative types. Diagnosing the pattern of GN is important because the outcome and treatment differ in different types. Primary causes are intrinsic to the kidney. Secondary causes are associated with certain infections (bacterial, viral or parasitic pathogens), drugs, systemic disorders (SLE, vasculitis), or diabetes. Signs and symptoms
Glomerulonephritis refers to an inflammation of the glomerulus, which is the unit involved in filtration in the kidney. This inflammation typically results in one or both of the nephrotic or nephritic syndromes. : 500

Nephrotic syndrome
The nephrotic syndrome is characterised by the finding of edema in a person with increased protein in the urine and decreased protein in the blood, with increased fat in the blood. Inflammation that affects the cells surrounding the glomerulus, podocytes, increases the permeability to proteins, resulting in an increase in excreted proteins.
When the amount of proteins excreted in the urine exceeds the livers ability to compensate, fewer proteins are detected in the blood – in particular albumin, which makes up the majority of circulating proteins. With decreased proteins in the blood, there is a decrease in the oncotic pressure of the blood. This results in edema, as the oncotic pressure in tissue remains the same. Although decreased intravascular oncotic (i.e. osmotic) pressure partially explains the patients edema, more recent studies have shown that extensive sodium retention in the distal nephron (collecting duct) is the predominant cause of water retention and edema in the nephrotic syndrome. This is worsened by the secretion of the hormone aldosterone by the adrenal gland, which is secreted in response to the decrease in circulating blood and causes sodium and water retention. Hyperlipidemia is thought to be a result of the increased activity of the liver. : 549

Nephritic syndrome
The nephritic syndrome is characterised by blood in the urine (especially Red blood cell casts with dysmorphic red blood cells) and a decrease in the amount of urine in the presence of hypertension. In this syndrome, inflammatory damage to cells lining the glomerulus are thought to result in destruction of the epithelial barrier, leading to blood being found in the urine. At the same time, reactive changes, e.g. proliferation of mesangial cells, may result in a decrease in kidney blood flow, resulting in a decrease in the production of urine.