Decreased bloodflow to the kidneys: (pre-renal ARF)

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A severe drop in blood pressure or blood volume can lead to ARF. Both cause a reduction in the perfusion or bloodflow to the kidney. This accounts for 50 to 60 percent of cases. Decreased blood pressure can occur during major surgery or as result of a heart attack or serious infection in the blood. A reduction in bloodflow can occur with massive bleeding and cause renal failure in this way. Dehydration caused by vomiting and diarrhoea is the commonest cause of prerenal ARF in children who suffer from gastroenteritis. Prerenal ARF may also occur in burn victims. Blood clots to the kidney can also interrupt the normal bloodflow to the kidneys, but are rare.

Damage to the kidney: (renal ARF)
This is when the kidney cells or its filtering units are damaged directly. It may be due to a sudden illness, inflammation of the kidneys, and injury or certain drugs and toxins. About 30 to 40 percent of ARF fall in this category. It is most often caused by acute tubular necrosis (ATN), where the filtering tubes of the kidney are damaged. Decreased bloodflow to the kidney during surgery, trauma or major infections can lead to ATN. Kidney diseases like glomerulonephritis can also cause kidney damage and lead to ARF. Sometimes medication can be toxic to the kidneys including certain antibiotics, anti-inflammatory drugs and contrast agents used in specific X-ray tests. The elderly, diabetic and other patients with underlying kidney disease are most at risk.

Blockage of the urine flow
Obstruction of the urine flow from the kidney, or within the kidney can also lead to ARF and accounts for about 5 percent of cases. The blockage can be caused by kidney stones, mass lesions like a tumor or an enlarged prostate. Doing a rectal or vaginal examination can reveal tumors of the reproductive organs and prostate. It is very important to exclude obstruction as a cause of renal failure because the treatment is considerably different. Special investigations like sonar of the kidney or pyelogram are used to determine the diagnosis. Pyelogram is an X-ray of the kidney taken after giving a contrast agent or “dye”.

Written by Dr K. Coetzee, reviewed by Dr R. Moosa, head of the Renal Unit, Tygerberg Academic Hospital.

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