Patients in the clinic are often alarmed by the presence of positive occult blood in their urine, thinking they have urinated blood. Clinically, positive urine occult blood is not the same as hematuria, and I will explain it to you in the context of this laboratory test. Hematuria refers to the presence of red blood cells in the urine, including microscopic hematuria and visual hematuria. The number of red blood cells per high-powered field of view is greater than 3 for microscopic hematuria, which is what we see on this sheet below: “Red blood cells (high-powered field of view)”, which is used to diagnose the presence of hematuria. If the red blood cells continue to increase, when the amount of blood in the urine exceeds 1 ml per liter, it will appear light red and is called hematuria by the naked eye. When red blood cells rupture, they release hemoglobin, and muscle damage releases myoglobin into the blood, and when they are excreted from the urine, the color of the urine becomes darker, which can be a strong tea color or even soy sauce color, and the urine occult blood test will be positive. However, some hospitals use a colorimetric method for the determination of urine occult blood, meaning that a patient’s darker urine may be recognized as positive for occult blood and does not indicate the presence of hemoglobin in the urine. This means that although this patient’s urinary occult blood was (++), we do not diagnose it as hematuria. Of course this is not to say that urinary occult blood is not important. Combining the patient’s medical history, symptoms and other ancillary tests, if only the urine is positive for occult blood and there are no other abnormal findings, the patient should not be alarmed and regular review is sufficient.