Almost every day, nephrologists encounter this kind of things: patients are worried and have no appetite because of positive urine occult blood or several “+” signs in urine occult blood found in physical examination or other reasons, some patients come to Beijing from thousands of miles away to seek treatment, some patients have been treated for years and worry that they will develop serious kidney disease or even Some patients have been treated for years, worrying that they will develop serious kidney disease or even uremia. First of all, we need to understand what exactly is occult blood in urine? To understand urinary occult blood, we must first understand urinary routine. Urine routine is the most common test in the hospital. Generally, the doctor will issue a urine routine test request form, and the patient will take some urine to the laboratory, and the result will come out soon. Urine routine mainly includes urine specific gravity, urine pH, urine protein, urine white blood cells, urine suberate, urine occult blood, urine red blood cells and so on. It can be seen that urine occult blood is one of the items in urine routine. Urine occult blood is simply a chemical reaction. It is tested in the laboratory by a dry chemical method called the “hemoglobin peroxidase method”, which has a sensitivity of 150-300 micrograms per liter. We know that the main component of red blood cells is hemoglobin, if there is hemoglobin in the urine, a chemical reaction will occur in the test, which means that our urine occult blood is called positive, or several “+” signs. This means that there may be red blood cells in the urine. Why do you say that there may be red blood cells in the urine, but not necessarily red blood cells? There are two main reasons: First, the target of the urine occult blood test —- is the hemoglobin in the urine. Although hemoglobin is the main component of red blood cells, it is not the same as red blood cells after all. For example, some reasons lead to the destruction of red blood cells in the blood lysis, releasing a large amount of hemoglobin, hemoglobin will pass through the kidneys, from the urine, if at this time to check the urinary routine, you will find positive urine occult blood, urine occult blood multiple “+” sign, but does not say that we have blood in the urine, red blood cells. Secondly, the target of urine occult blood test —- is not only the hemoglobin in the urine. The target of urine occult blood test is not only hemoglobin in urine, but also myoglobin, heat-unstable enzymes, many oxidants, bacteria, etc. in urine. So when the urine contains these components, the urine occult blood is also positive, also several “+” signs, obviously, this time the urine occult blood positive is definitely not the presence of blood, red blood cells in the urine, medical called false positive results. I don’t know if you noticed, but in addition to urine occult blood, there is also a urine red blood cells in the urine routine. This means that urine occult blood and urine red blood cells are not one concept, but two different things. Urine occult blood is a chemical reaction, it is only a reference for us to diagnose if there is hematuria or if there are red blood cells in the urine. Urine red blood cells are what the doctor sees with the naked eye under a microscope, not a chemical reaction, and a few red blood cells are a few. If there is blood in the urine or if there are red blood cells in the urine, the main thing to look at is the urine red blood cells in the urine routine. Healthy people have red blood cells in their urine, but the number does not exceed 3 per high-powered view. If the number of red blood cells in urine is greater than 3/high magnification, it is basically said to be hematuria, while in many cases, urine occult blood is not “blood”. In short, occult blood in urine is not the same as hematuria or blood in urine, and should always be looked at by an experienced doctor.