Normally, urine does not contain any blood. One of the most common causes of blood in the urine, is infection or inflammation of the urinary tract itself. Some people have other symptoms when they have blood in their urine, whereas other people will feel completely well with no other symptoms. But it is always abnormal and should be further investigated by a healthcare professional.
Occult blood in urine can be due to urinary tract (bladder) infection, swelling in the filtering system of the kidneys, stone in bladder or in a kidney, blood disease, like sickle cell anemia, polycystic kidney disease, certain medicines and tumors in the urinary tract.
The occult blood test will react positively in the presence of red blood cells (hematuria), free hemoglobin (hemoglobinuria) or free myoglobin. Further evaluation of the urine sediment is needed if a positive test result is found.
Microscopic examination of the urinary sediment shows intact red blood cells, but free hemoglobin produced either by hemolytic disorders or lysis of red blood cells is not detected. Therefore, chemical tests for hemoglobin provide the most accurate mean for determining the presence of blood. Once blood has been detected, the microscopic examination can be used to differentiate between hematuria and hemoglobinuria.
Most commonly, hematuria is the cause of the positive occult blood test result. When blood is visible to the eyes (pink, brownish or red urine), it is called "gross hematuria" or "macroscopic haematuria". If the blood can only be detected with laboratory testing, it is called "microscopic", or "non-visible".
The blood usually come from somewhere within the urinary tract – the kidneys, bladder or the tubes that urine passes through. It is often the result of a urinary tract infection (UTI), such as cystitis. The most common symptoms are pain passing urine and passing urine more often than normal. You may also have pain in your lower tummy and a high temperature (fever).
Kidney infections (also known as pyelonephritis) usually occur as a complication of a bladder infection. Symptoms of kidney infections are usually more severe than with a urinary tract infection. Often there is a very high temperature (fever) and pain in the side of your tummy (abdomen) or over the side of your back.