The causes of hematuria in children are complex and the diagnosis is not easy. It needs to be seen and judged by a nephrologist, and a series of tests such as renal function tests, nephrostomy, renal ultrasound, renal puncture, etc. are needed if necessary. Even if the diagnosis is clear, simple hematuria and nutcracker usually do not require treatment, and avoiding the triggering factors as much as possible is sufficient. One item of urine occult blood in urine analyzer is affected by various components in urine, which is prone to false positives, and dietary drugs will have an effect, and it is only applicable to the preliminary screening of urine test. Generally positive urine occult blood will require microscopic examination: centrifugal urine under high magnification, the number of red blood cells more than 3 is the diagnostic criteria for hematuria. Generally speaking, if there are more red blood cells in the urine, the more the relative occult blood count will be added. However, the number of red blood cells in urine or the strength of positive urine occult blood is not particularly correlated with kidney function, and blood tests for kidney function should be done to understand whether kidney function is normal or not. The causes of “hematuria” are more common in pediatric clinics: 1. Transient hematuria due to viral infection Hematuria may occur during or 1-2 weeks after upper respiratory tract viral infection. The hematuria is mild, with 3-5 red blood cells visible microscopically, and is not accompanied by other clinical symptoms that may be produced by kidney disease, and is usually found during laboratory tests. There is no need to do other related tests for the time being, and most of them return to normal after 1-2 weeks. If there are still red blood cells on the recheck, you can see a nephrologist for further examination. Some cold medicines can also cause transient hematuria, which can be handled similarly. 2, allergic purpura renal comorbidity (purpura kidney) is common in the acute phase or recovery of allergic purpura, there can be hematuria, and some have protein urine. The incidence of this comorbidity is still relatively high in patients with allergic purpura, so patients with allergic purpura routinely have to check their urine. The kidney of allergic purpura is called purpura kidney, purpura kidney varies in severity, lighter, without treatment can recover by itself, but there are heavier, need hormone and other special treatment. If combined with purpura kidney, it is necessary to review the urine regularly for a longer period of time to avoid delaying the disease. 3, post-streptococcal nephritis Streptococcal infection (purulent tonsillitis, impetigo, etc.) is one of the most common causes of induced nephritis. Post-streptococcal nephritis is often accompanied by not only hematuria but also proteinuria, often with swelling, and high blood pressure when the doctor examines the child. The diagnosis of acute nephritis often requires hospitalization and regular review after discharge. 4. Nutcracker phenomenon This is a phenomenon in which the left renal vein is compressed between the abdominal aorta and the superior mesenteric artery, and the stagnant venous blood forms abnormal traffic between the venous sinus and the lower renal calyces and hematuria occurs. It usually occurs in school-age children with a thin body, and the hematuria is obvious after activity, and it occurs repeatedly, but it is only simple hematuria without other abnormalities such as urine protein, and the diagnosis can be clearly made by ultrasound. No treatment is needed after the diagnosis is clear. 5.Simple hematuria (benign hematuria) Only red blood cells in the urine are more than normal, hematuria occurs repeatedly and is often accompanied by upper sensation when hematuria occurs. No other clinical symptoms: no swelling hypertension, no purpura. No other abnormalities in urinary routine and kidney function, and no abnormalities in ultrasound, that is, simple hematuria (benign hematuria). Children with simple hematuria should preferably have routine urinalysis when upper respiratory tract infections occur, or have their urine rechecked once every 3-6 months. There are, of course, more rare diseases that cause hematuria in children, and the diagnosis is not easy. A nephrologist is needed to make a diagnosis, and if necessary, a series of tests such as renal function tests, nephrostomy, renal ultrasound, and renal puncture are required. Even if the diagnosis is clear, simple hematuria and nutcracker usually do not require treatment, and avoiding the triggering factors as much as possible is sufficient. In contrast, hematuria caused by various nephritis needs to be treated for nephritis, and sometimes very mild microscopic hematuria is left behind, which can only be reviewed regularly without further treatment. The diagnosis of the cause of hematuria is much more important than the treatment of hematuria, and regular follow-up is especially important for children with hematuria that has no clear cause for the time being. No treatment does not mean that follow-up is not necessary, and regular review is essential.