The number of red blood cells per high-powered field of view is generally normal within 3, and if more than 3 are present, the red blood cells are over the limit. If you see more red blood cells under the microscope and it is difficult to count them, this situation is called red blood cell full field. A full field of red blood cells indicates hematuria. There are many causes of hematuria, such as IgA nephropathy, acute nephritis, chronic nephritis, and other non-nephritic diseases that can also cause hematuria, such as kidney stones, urinary tract infections, urinary tract tumors, and so on. Some diseases affect the hematological system, especially the coagulation, and can also cause bleeding from the urinary tract leading to hematuria, such as systemic lupus erythematosus, thrombotic thrombocytopenic purpura, hemophilia, etc. That is, there are many diseases that can cause red blood cells to fill the field of view, and they need to be identified one by one, and then dealt with according to the cause, otherwise it is easy to miss and misdiagnose.