Hematuria is the presence of red blood cells in the urine. Microscopic hematuria is called microscopic hematuria when only an increase in red blood cells is found; the naked eye can see the urine in the color of “meat wash” or blood or even clots is called “hematuria”. Generally, when 1000mL of urine contains 1mL of blood, it can appear as sarcoid hematuria. The color of sarcoid hematuria is related to the acidity and alkalinity of urine; neutral or weakly alkaline urine has a bright red color or is like meat wash, while acidic urine is like strong tea or sooty water. Microscopic hematuria criteria are: ≥3/HP in centrifugal urine. Common causes of hematuria: Renal diseases various primary glomerular diseases: acute and chronic glomerulonephritis, Alport syndrome, thin basement membrane disease, IgA nephropathy, pulmonary hemorrhage-nephritis syndrome, etc. Infections: renal tuberculosis, pyelonephritis. Malformation: renal vascular malformation, congenital polycystic kidney, wandering kidney, renal prolapse, hydronephrosis, etc. Tumor: renal embryonal tumor, renal calyx vascular tumor, etc. Renal vascular lesions: renal vein thrombosis, left renal vein compression syndrome (Nutcracker phenomenon). Injury: renal contusion and other injuries Drugs: nephrotoxic drugs such as aminoglycoside antibiotics, bacitracin, salicylic acid preparations, sulfonamides, phenytoin sodium, cyclophosphamide, etc., can cause renal or urinary tract damage producing hematuria. Urinary tract disease infections: cystitis, urethritis, tuberculosis. Stones: ureteral stones, bladder stones. Tumors, polyps, diverticula, foreign bodies, etc. Systemic diseases Hemorrhagic diseases: diffuse intravascular coagulation, thrombocytopenic purpura, hemophilia, neonatal natural bleeding disorder, aplastic anemia, leukemia, etc. Cardiovascular diseases: congestive heart failure, infective endocarditis. Infectious diseases: scarlet fever, typhoid fever, epidemic hemorrhagic fever, infectious mononucleosis, fulminant epidemic meningitis, and post-infectious nephritis due to Mycoplasma pneumoniae, Mycobacterium tuberculosis, hepatitis virus, leptospira, etc. Rheumatic diseases: systemic lupus erythematosus, allergic purpura, polyarteritis nodosa, rheumatic nephritis. Nutritional diseases: vitamin C deficiency, vitamin K deficiency. Allergic diseases: dietary allergies, such as milk or pineapple allergy. Other diseases: such as hereditary capillary dilation, transient hematuria due to strenuous exercise, idiopathic hypercalciuria, etc. In adults, infections such as acute cystitis (mostly in women), urological tumors (mostly without painful urination), urinary stones (back pain with microscopic or carnal hematuria), and prostatic hyperplasia are common. In children, it is mostly glomerulonephritis. Regardless of the etiology, once you have carnal hematuria, it is a signal for you to seek medical attention as soon as possible, remember!