Hematuria or haematuria is defined as the occurrence of blood or red blood cells in the urine. The word hematuria is derived from Greek haima "blood" and ouron "urine". Hematuria can be visible to the naked eye and may appear red or brown , or it can be microscopic . The origin of the blood that enters and mixes with the urine can arise from any anatomical site within the urinary system, including the kidney, ureter, urinary bladder, and urethra, and in men, the prostate. Common causes of hematuria include urinary tract infection , kidney stones, viral illness, trauma, bladder cancer, and exercise. The underlying causes of hematuria can be divided into glomerular and non-glomerular causes, referring to the involvement of the glomerulus of the kidney. Notably, not all red urine is hematuria. Other substances such as certain medications and foods can cause urine to appear red. Menstruation in women may also cause the appearance of hematuria and may result in a positive urine dipstick test for hematuria. Additionally, a urine dipstick test may be falsely positive for hematuria due to other substances in the urine such as myoglobin during rhabdomyolysis. A positive urine dipstick test should be confirmed with microscopy, where hematuria is defined by three of more red blood cells per high power field. When hematuria is detected, a thorough history and physical examination with appropriate further evaluation can help determine the underlying cause.

血尿是指离心沉淀尿中每高倍镜视野≥3个红细胞，或非离心尿液超过1个或1小时尿红细胞计数超过10万，或12小时尿沉渣计数超过50万，均示尿液中红细胞异常增多，是常见的泌尿系统症状。原因有泌尿系炎症、结核、结石或肿瘤、外伤、药物等，对机体影响甚为悬殊。轻者仅镜下发现红细胞增多，称为镜下血尿；重者外观呈洗肉水样或含有血凝块，称为肉眼血尿。通常每升尿液中有1mL血液时即肉眼可见，尿呈红色或呈洗肉水样。