Testing for blood in the urine includes testing for intact erythrocytes (red blood cells) and the detection of hemoglobin from intact or broken erythrocytes. The test also detects myoglobin, a muscle protein. Blood is very often present in vaginal secretions, which can contaminate a urine specimen. A positive blood test will usually be followed by an examination of the specimen under a microscope (urine sediment). The presence of squamous cells under a microscope (see that section) indicate that a contaminated specimen may be responsible for some or all of the blood detected.
If not the result of contamination, a positive blood test with microscope confirmation of the presence of intact erythrocytes may indicate one of many kidney and urinary duct disorders (infection, inflammation of the bladder [cystitis], kidney stone, tumour or urinary tract cancer, etc.). The presence of hemoglobin in the absence of red blood cells under the microscope may indicate hemolytic disease in the blood or muscle damage (poisoning, intense exercise and other muscle injuries). It is also possible that the very diluted urine sample (urine density of less than 1.006) or poor storage conditions are responsible for ruptured erythrocytes in the urine sample.