Blood in Urine

Urine sample cut with dark brown coloured urine

Blood in urine
Image by James Heilman, MD (CC BY-SA 3.0)

Blood in urine may be seen as a red tinge, dark red colour or even blood clots, but often the amount present is so small that no difference in colour can be detected by the patient.

Doctors can test for extremely small amounts of blood in urine (haematuria) very simply by using a plastic strip with a spot of chemical on it which changes colour if blood is present. The greater the colour change, the greater the amount of blood present in the sample of urine. Examining the urine under a microscope will reveal red blood cells if blood is present.

Diseases of the kidney, ureter (tube from kidney to bladder), bladder, urethra (tube from bladder to outside) and prostate may cause bleeding into the urine. Blood may also find its way into the urine by contamination of a sample during a woman’s menstrual period, bleeding piles or from a bleeding sore on the genitals. Red coloured foods (e.g. beetroot and some medications) may give a false impression of blood.

By far the most common cause of blood in a urine sample is a bacterial bladder infection (cystitis). The patient will experience a fever, feel pain low down in the front of the belly, will pass urine more frequently, and pain will be felt when passing urine. Virtually every woman will have cystitis at some time, but it is far less common (and usually indicates more serious disease) in men.

Pyelonephritis is a bacterial infection of a kidney. The symptoms include a fever, loin pain (usually only on one side), frequent passing of urine, general tiredness and sometimes blood in the urine.

Glomerulonephritis is a degeneration of the filtering mechanism (glomeruli) of the kidney that occurs in two forms – acute and chronic. Acute glomerulonephritis is often triggered by a bacterial infection (eg. tonsillitis) but may start as a result of other diseases in the body. The patient feels tired, has no appetite, develops headaches and has a low-grade fever. Some patients do not recover from acute glomerulonephritis, and are considered to have chronic glomerulonephritis. There are usually no symptoms until the kidneys start to fail and excessive levels of waste products build up in the bloodstream.

Other causes of blood in the urine include prostatitis (bacterial infection of the prostate gland), a stone in the kidney, extremely vigorous exercise (eg. running a marathon) and a tumour or cancer that develops anywhere in the urinary system (eg. renal cell carcinoma).

An injury to the kidneys, bladder or genitals (eg: car accident, fall, sport) may cause damage to these organs and bleeding. If the bleeding persists for more than a couple of days, investigations are necessary to find the exact site of bleeding so that it can be corrected.

Patients who are taking warfarin to thin their blood because of a risk of blood clots, and patients who have poor blood clotting due to other diseases (eg: haemophilia) often have small amounts of blood found in their urine.

Some people with haematuria can have no cause found for the condition, and it is thought that they may have been born with kidneys that leak blood into the urine without any disease being present. This diagnosis is only made after all other possibilities are excluded.

Rare causes of haematuria include haemolytic anaemia, tuberculosis involving the kidneys, septicaemia, autoimmune diseases (eg. systemic lupus erythematosus, polyarteritis nodosa, rheumatoid arthritis, scleroderma), leukaemia, paroxysmal nocturnal haemaglobinuria and bilharzia (transmitted by a species of snail that is found in freshwater streams, rivers and lakes in Egypt, tropical Africa, the Caribbean and South America).

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