A small number of red blood cells can be present in normal human urine as 0-2 cells/high magnification field. Hematuria is a higher than normal number of red blood cells in the urine, i.e., the number of red blood cells in the urine: >3/high magnification field or >8000/mL in centrifuged urine and >1-2/high magnification field in non-centrifuged urine. The test is performed by taking 10mL of fresh clean mid-stream urine (morning urine is preferred), centrifuging it and taking the sediment for microscopic examination. Currently commonly used urine analyzers use the test paper method to detect urinary occult blood, the principle of which is to use the peroxidase-like activity of hemoglobin and the color-presentation reaction of the test paper for semi-quantitative analysis. However, false negatives can be presented if reducing substances (such as vitamin C > 50 mg/L) are present in the urine, and false positives can be presented if free hemoglobin, myoglobin and peroxidase are present in the urine. Therefore, a positive urine occult blood cannot be used as a basis for the diagnosis of hematuria, and can only be used as a screening test, and the diagnosis of hematuria needs to be confirmed by urine sediment microscopy.