Apart from disorders that are present at birth, such as polycystic kidney, most causes of kidney malfunction involve stones (calculi), tumours, infection or inflammation (or a combination of these). A kidney stone, knownly as a renal calculus, is an aggregation of solid matter that has crystallized or solidified as salts from concentrated urine. Calculi form in the kidney, from where they may pass into the ureter or pass down into the bladder. Typical calculi salts include oxalates and phosphates of calcium or magnesium; other stones consist of uric acid or urate salts. An abnormally high level of calcium in the is often the cause.
Small stones cause little or no discomfort and may be passed in the urine. Larger stones may block the ureter, causing a back-pressure of urine to the kidney and the excruciating pain of renal colic. Stones may be removed by direct surgical intervention, crushed in situ by litholapaxy or, in a new technique, broken up painlessly using ultrasonic shock waves. Kidney tumours may also reveal their presence only after causing some sort of obstruction to urine flow. In older men, obstruction of urine flow may also be the result of enlargement or a tumour of the prostate gland (which restricts flow along the urethra). Infections of the kidney – often with accompanying inflammation – include pyelonephritis and nephritis (Bright’s disease). As well as back pain, symptoms may include proteins orin the urine (haema-turia). Any accompanying oedema, swelling of the body because of fluid retention, points to a malfunction of the kidney’s filtering system, a combination of symptoms known as nephrotic syndrome, or nephrosis, which may also occur with diabetes or poisoning.
Pyelonephritis is usually caused by a bacterial infection, sometimes as a complication of bladder inflammation (cystitis). The inflammation of nephritis, more properly called glomerulonephritis, is often an allergic reaction to a streptococcal infection else where in the body, such as the throat. Other possible causes are high blood pressure or poisoning by heavy metals or certain drugs. High blood calcium levels, as occur in gout, kidney stones and disorders of the parathyroid gland, may be a contributing factor.