In the pediatric clinic, we often see some children with recurrent hematuria or persistent hematuria, and their parents are very anxious about this, and they go to several hospitals, take a lot of medicine, treat for months or even years, but still can’t be cured, and they can’t tell what disease their children have. So, how should hematuria be diagnosed and treated? For hematuria, especially isolated hematuria (no other clinical manifestations other than hematuria, such as proteinuria, swelling, oliguria, hypertension, etc.), it is important to follow the diagnostic process strictly so that the diagnosis will not be misdiagnosed and will not be missed. Step 1: To determine whether it is true hematuria? Or pseudohematuria? There are two types of pseudohematuria, one is that there is some kind of pigment inside the urine that causes the urine to be red; for example, certain drugs that can change the color of the urine. One condition is that the blood in the urine is contaminated by bleeding near the urethra, such as menstruation in older girls, bleeding from anal fissures, etc. Step 2: If it is true hematuria, it is important to determine whether the hematuria is caused by systemic factors? Or is it confined to the urinary system? Blood in urine due to blood disorders has been encountered in the clinic before. In fact, hematuria can be caused by thrombocytopenia, abnormal coagulation mechanism, and vascular lesions. Specifically, common diseases that cause hematuria include leukemia, hemophilia, thrombocytopenic purpura, scurvy, etc. These diseases often have bleeding in other parts of the body, and the diagnosis can also be determined by checking blood routines and, if necessary, bone marrow aspiration. Step 3: If the bleeding is localized in the urinary system, it is important to figure out where the bleeding is located. Anatomically speaking, the urinary system is divided into four parts: kidney, ureter, bladder and urethra, and theoretically we should also determine from which part the hematuria comes; however, in terms of the incidence and severity of the disease, we prefer to divide the source of hematuria into glomerular hematuria and non-glomerular hematuria, and sometimes we also generalize it as “renal hematuria Sometimes we also generally refer to “renal hematuria” and “non-renal hematuria”. There are two practical methods to determine glomerular hematuria and non-glomerular hematuria, one is to observe the morphology of red blood cells in the urine with a phase contrast microscope (our hospital test is called “urine sedimentation four”), this method can have human error, that is, it is prone to sampling error, and the objectivity is not very high, it is generally believed that If the deformation rate of red blood cells exceeds 70%, it is considered glomerular hematuria, and if the deformation rate is less than 30%, it is considered non-glomerular hematuria, but in clinical practice, the deformation rate of red blood cells is often between 30% and 70%, which requires repeated testing; and there is another very important issue, if the hematuria is mild, then the reference value of the deformation rate is not much, and when the hematuria is heavy, the deformation rate of the red blood cells observed is less. The observed red blood cell deformation rate is of greater significance. There is also a method to detect some information of urine red blood cells with flow cytometric urine sediment test, such as 70% red blood cell forward scattered light intensity (RBC-P70Fsc), the unit of this parameter is channel, abbreviated as ch. The size of urine red blood cells can be judged according to the position of the curve crest of this parameter, so as to identify glomerular hematuria or non-glomerular hematuria. Generally, RBC-P70Fsc≤70ch is small red blood cells (Dysmorphic), i.e. non-homogeneous red blood cells, which indicates that the hematuria is glomerular; RBC-P70Fsc≥100ch is homogeneous red blood cells (isomorphic), which is non-glomerular hematuria; RBC-P70Fsc between 70-100ch which is mixed. This flow cytometric assay, which is not influenced by subjective factors and has a very high reproducibility. It should be because urine may be diluted and concentrated (varying in thinness and consistency), so multiple tests are needed to get accurate results. If the child has glomerular hematuria, it often has three characteristics: (i) the hematuria is aggravated by infection, (ii) it is suddenly aggravated by infection and then slowly decreases, which can last 1-2 weeks, and (iii) in the usual urine red blood cells will not be in the normal range; for isolated glomerular hematuria, there are three most common diseases, IgA nephropathy, benign hematuria, and Alport syndrome; all three diseases have some heredity If the hematuria is serious and you want to accurately identify these three diseases, the best way is to do a kidney tissue biopsy, the typical pathology of IgA nephropathy is thylakoid proliferative glomerulonephritis with IgA deposits in the thylakoid area. The typical pathology of IgA nephropathy is thylakoid glomerulonephritis with deposition of IgA in the thylakoid region, the typical manifestation of benign hematuria is basement membrane thinning, and immunofluorescence testing in Alport syndrome can reveal abnormal changes in the glomerular basement membrane or IV collagen, the major collagen component of the skin. However, because renal biopsy is, after all, an invasive test, it is generally not recommended for children with less severe hematuria. Clinically, the possibility of IgA nephropathy, benign hematuria or Alport syndrome is mainly determined by the presence of patients with kidney disease in the family, the presence of episodes of granulomatous hematuria, and the degree of aggravation of hematuria after infection, which often requires dynamic observation for 3-6 months. If the child has non-glomerular hematuria, it has the following characteristics: (1) it tends to worsen after exercise, (2) the hematuria can be sudden and abrupt, and (3) there can be no hematuria in general; the most common diseases are hypercalciuria and Nutcracker phenomenon. If hypercalciuria is suspected, 24-hour urinary calcium should be measured 2-3 times continuously, if more than 2 times is greater than 0.1mmol/(kg.d), it is increased urinary calcium; children with hypercalciuria can have increased intestinal absorption or kidney leakage, such children can often have kidney stones or even gallstones, and can have a family history; they need to take some medication for treatment and dynamic observation. Nutcracker phenomenon refers to the small angle between the abdominal aorta and superior mesenteric artery, and the left renal vein just passes through this angle into the inferior vena cava; because of the small angle, it can affect the return flow of the renal vein to a certain extent, thus causing hematuria. Ultrasound of renal vein can be done to determine whether there is a nutcracker phenomenon, but ultrasound examination is more subjective, and the accuracy of detection is closely related to the doctor’s technique, experience, and responsibility, etc., so multiple examinations are needed if necessary. There are three parameters that can be used to determine the presence or absence of the nutcracker phenomenon: (1) the angle between the abdominal aorta and the superior mesenteric artery; (2) the ratio of the diameter of the renal vein at the renal portal and the renal vein after crossing the superior mesenteric artery; and (3) the ratio of the blood flow velocity between the renal vein at the renal portal and the renal vein after crossing the superior mesenteric artery; combining these three parameters, it is possible to determine the presence or absence of the nutcracker phenomenon in children. It is worth mentioning that the nutcracker phenomenon is only an anatomical change, and the presence of nutcracker changes does not necessarily mean that hematuria is present. If the hematuria caused by nutcracker phenomenon is not very serious, no special treatment is needed. Of course, in addition to the above-mentioned common hematuria, there are other special cases, such as tumors, hydronephrosis, and renal cysts. There are also some extremely special cases, such as purpura nephritis with hypercalciuria or the nutcracker phenomenon, etc. Clinicians must analyze them from multiple aspects to avoid missing and misdiagnosis. The various tests to determine the source of hematuria covered above, urine flow cytometry, ultrasound to detect the nutcracker phenomenon, urine calcium measurement, and kidney CT are all routine tests in our hospital, and the source and nature of hematuria can be determined to the maximum extent for children with hematuria who are usually hospitalized for 7-10 days.