Before there is an answer as to why hematuria occurs, it is important to first understand what hematuria is. Generally speaking, there are no red blood cells or occasional individual red blood cells in the urine of normal people. If there is blood mixed in the urine, the number of red blood cells per high-powered field of view in the microscopic examination of the urine sediment after centrifugal precipitation processing is called hematuria if it exceeds 3. When hematuria is light, the color of urine is not obviously abnormal, and it is difficult for the patient to find out by himself. Only after microscopic examination can it be determined that there are red cells in urine, and it reaches the standard of hematuria (more than 3 red cells per high-powered field), which is medically called microscopic hematuria. Once hematuria appears, the cause should be investigated. Some patients sometimes have microscopic hematuria, but not necessarily urological diseases, such as upper respiratory tract infections or other febrile diseases caused by viral or bacterial infections, dehydration or after strenuous exercise, can have temporary microscopic hematuria, but carnal hematuria is definitely a problem somewhere in the body. There are many factors that can cause hematuria, such as inflammation of the urinary system, stones, tuberculosis, tumors, malformations, trauma, vascular abnormalities, parasites, etc. In addition, lesions in the adjacent tissues of the urinary tract, such as acute appendicitis, acute tuberculitis, colonic diverticulitis or tumors in adjacent organs, can also cause hematuria, but microscopic hematuria is common. If hematuria is accompanied by an increase in the number of urination, urgency to hold urination, painful urination, etc., especially in patients with painful urination, it is mostly due to urinary tract infection, stones, etc. This type of hematuria is called painful hematuria; hematuria without painful urination is called painless hematuria, which is mostly seen in nephritis, renal tuberculosis, urological tumors, etc.; if older patients develop painless carnal hematuria, special attention should be paid to it and a comprehensive examination must be performed to exclude it. A comprehensive examination must be conducted to rule out the possibility of malignant lesions. In addition, many systemic diseases, such as hematological lesions, infectious diseases, immune diseases, cardiovascular diseases, endocrine diseases and physical and chemical injuries, can also cause hematuria. What does pus urine, tubular urine and crystalluria refer to? When urine contains a large number of pus cells, i.e., white blood cells, such as infectious inflammation, immune diseases, and secondary infections. Tubular urine is a cylindrical substance formed in the urine by the solidification of proteins. When there is an increase in this cylinder in the urine or when other types of tubes appear in the urine, it is called tubular urine. Some common types of tubular urine include cellular, granular, fatty, and clear tubular. Increased tubularity in urine, especially granular tubularity, often indicates damage to the kidney parenchyma. Crystalluria is the precipitation of salt crystals from the urine and can be detected during routine urinalysis. Most of the crystalluria is formed by the precipitation of salt crystals in the urine due to factors such as concentration of urine after water loss, low temperature or acid exposure. Common urine crystals include magnesium ammonium phosphate crystals, mainly seen in urinary tract infections and infected kidney stones, uric acid crystals, which are indicative of disorders of uric acid metabolism; calcium oxalate crystals, which are mostly seen in hyperoxaluria and calcium oxalate stones; and sulfonamide crystals, which are mostly seen in patients taking sulfonamide drugs.