nephritis
Meaning of nephritis: Not one disease but a family of them, sharing inflamed kidney tissue and a set of clues that appear in the urine.
Definition of nephritis
Nephritis is inflammation of the kidney, most often of the tiny filtering units that clean the blood. Inflamed tissue filters poorly, so protein and red cells escape into the urine while waste products build up in the blood. Immune attack, reactions to medicines and bacteria traveling up from the bladder are the usual causes.
What is actually inflamed?
Each kidney holds around a million filtering units. Every one of them has a knot of tiny blood vessels, the glomerulus, wrapped in a capsule and draining into a long tubule that fine-tunes what leaves as urine. Between the tubules sits supporting tissue laced with more small vessels. Nephritis can settle in any of these, and where it settles decides what the illness looks like. Inflammation of the filters lets protein and red cells slip through into the urine. Inflammation of the supporting tissue disturbs the tubules instead, so salts and acid are handled badly while protein loss stays modest.
What causes it?
| Type | What is inflamed | Usual trigger |
|---|---|---|
| Glomerulonephritis | The filtering knots | Immune deposits, often weeks after a throat or skin infection |
| Lupus nephritis | The filtering knots | Autoimmune disease attacking kidney tissue |
| Interstitial nephritis | Tissue between the tubules | A reaction to a medicine, or to infection |
| Pyelonephritis | Kidney and its collecting system | Bacteria reaching the kidney from the bladder |
Only the last of those is an infection of the kidney itself. That is the point most often misread, because the ending sounds like it should mean germs while it means nothing more than inflammation.
How does it show itself?
Urine that looks smoky, pink or like cola points to red cells crossing the filters. Urine that froths persistently points to protein. Fluid held in the tissues puffs the face and ankles, blood pressure climbs, and the volume passed may fall. Kidney infection adds fever, shivering and pain in the flank. Many milder cases produce nothing a person notices and are found when a urine sample is tested for another reason. Blood tests of how well the kidneys clear waste, an ultrasound scan and often a biopsy separate the types, since the appearance under the microscope is what names the disease. Where inflammation follows a blockage, drainage through a nephrostomy forms part of managing it, and a renal dietitian is commonly involved in advice on salt, protein and fluid once kidney function is reduced.
Also known as
Used in a sentence
A renal biopsy was arranged to establish the cause of the nephritis.
Good to know
The ending -itis marks inflammation rather than infection, and most forms of nephritis are not infections, so the cause and the treatment differ sharply between conditions that share the name.
Word origin
Where “nephritis” comes from
Combines the Greek nephros, meaning kidney, with the ending -itis, which marks inflammation.