In the clinic, we often encounter some patients (not really patients) repeatedly ask the same question, is urine occult blood several (+) is nephritis? Some people are troubled by several “+” signs of urine occult blood for a long time and worry that they have a serious kidney disease and will develop into uremia in the future. As a whole, they are worried and seek medical help everywhere, and even come from far away to Beijing for treatment. As a result, the examination continued and nothing happened. What is occult blood in urine? Urine occult blood is one of the routine urine tests. It is the most common test in hospitals. The doctor writes a request for a routine urine test, the patient takes some urine and sends it to the laboratory, and the results are soon available. The principle of urine occult blood test is a chemical reaction method, which is called dry chemical method in medical science. Urine occult blood is detected using the “hemoglobin peroxidase method” with a sensitivity of 150-300 micrograms per liter. The main component of red blood cells is hemoglobin, so if there is hemoglobin in the urine, a chemical reaction will occur in the test and the urine will appear positive for occult blood, or a few “+” signs, indicating that there may be red blood cells in the urine. But you can’t say that there must be red blood cells, or that there is hematuria, or that it is nephritis hematuria. First, urine occult blood detects the hemoglobin in the urine. Although hemoglobin is the main component of red blood cells, it is not the same as red blood cells. For example, some causes lead to the lysis and destruction of red blood cells in the blood, releasing a large amount of hemoglobin, which will pass through the kidneys and be excreted from the urine, and multiple (+) signs of urine occult blood will be found when checking the urine routine, but it does not mean that there are red blood cells in the urine, or blood in the urine. Secondly, the target of the urine occult blood test is not only hemoglobin, but also myoglobin in the urine, heat-unstable enzymes, many oxidants, bacteria, etc., which also react to chemical reagents and appear positive for urine occult blood, also several (+) numbers. Obviously, a positive urine occult blood at this time is definitely not the presence of blood or red blood cells in the urine, which is medically called a false positive. As seen above, there are two main cases of positive urine occult blood: 1, there are really red blood cells in the urine, there is that is red blood cell urine; 2, hemoglobinuria or false positives to the chemical reaction of some substances in the urine. And there is a high percentage of false positive urine occult blood. That’s why so many people have urinary occult blood several (+) signs. That’s why routine urine tests are usually only used for screening of kidney disease, to find out as many patients with kidney disease as possible, and then in further tests, with the aim of reducing the number of patients with disease not found, and the number of missed diagnoses. In other words, urine occult blood just means that the urine may be red blood cells, to determine if there must be red blood cells how? Another item in the urine routine is urine red blood cells. This means that urine occult blood and urine red blood cells are not a concept, but two different things. A few (+) of urine occult blood also has nothing to do with the severity of the hematuria. Does the presence of red blood cells in urine necessarily mean nephritis? Neither. Whether it is nephritis or not depends mainly on the number and pattern of red blood cells. It is usually diagnosed as nephritis hematuria only when there are more than 5 red blood cells (5/HPF) in each high magnification field of the microscope and the morphology is deformed red blood cells.