Normal urine is clear and slightly yellow in color. It consists of great amount of water and certain inorganic elements (potassium, natrium, etc.), and organic substances (urea, creatinine, etc.).

Appearance of red blood cells (RBC) in urine is called hematuria. Small amount of RBC in urine cannot be observed by human eye, because the color of urine is still normal. The RBC can be seen only by microscope, called microscopic hematuria. When the RBC exceed 1 milliliter per liter of urine, the urine becomes bright red in color, called naked eye hematuria.

Hematuria is a signal for many diseases or abnormal condition of the body. There is no RBC in normal urine. Hematuria can be seen occasionally after strenuous exercise, heavy labor work or standing for a long period of time. However, frequent hematuria should be cautioned.

The most common cause of hematuria is a diseased urinary system. Three-glass test of urine is probably able to know where the RBC originates. Asking patient to urinate, the first, middle, and last courses of urine are collected by three glasses, respectively. If the urine in the first glass contains RBC, the blood may come from preurethra; if the urine in the third glass contain RBC, the blood may come from bladder or posturethra; if urine in all glasses contain RBC, the blood may come from above the bladder, including kidney and ureter.

Hematuria in children is often caused by acute glomerulonephritis, accompanying with proteinturia, swollen, and increased blood pressure. Pyelonephritis or urocystitis caused by bacterial infection have pyuria (white blood cells in urine), fever, shiver, lower back pain, frequency of micturition (increased frequency of urination), urgency of urination, urodynia (pain during urination), etc., besides the hematuria. Hematuria caused by renal tuberculosis (TB) usually accompanying with low fever, night sweet, etc., as well as other organs' TB (such as TB of epididymis, active pulmonary TB).

In case. a patient above 40 has painless hematuria, he should be considered having tumor. Under this condition, the patient usually may have fatigue, weight loss, etc. Renal colic (angina) has radiation toward lower abdomen, pudendum, and medial side of thighs. Renal colic is the characteristics of nephrolithiasis (kidney stone) and ureterolith (ureter stone). Vesical calculus (or cystolith, bladder stone) and urethral calculus (urethra stone) appears urodynia, discontinuation of urination, and difficult urination. Urinary stone is a common cause of hematuria.

Individual of age over 40 years who has hematuria accompanying with fatigue and weight loss should be considered having tumor. Renal colic (angina) usually has radiation toward lower abdomen, pudendum, and medial side of the thigh. Renal colic is the characteristics of the nephrolithiasis (kidney stone) and ureterolithiasis (ureter stone). Vesical calculus (bladder stone) and urethral calculus (urethra stone) have urodynia, discontinuation, and difficult urination. Lithogenesis of urinary system also is the common cause of hematuria.

Diseases outside the urinary system can also induce hematuria. Acute appendicitis and female pelvic inflammation can appear transient microscopic hematuria. Rectum cancer, colon cancer, and malignant tumor of ovary may involve in the urinary system, causing continuous and marked hematuria. Hematuria complicating nose and gum bleeding and hemorrhagic spots in the skin may indicates existence of hemorrhagic diseases, such as thrombocytopenia (decreased platelet) and leukemia. Other diseases, like desmosis (disease of connective tissue), cardiovascular diseases are able to cause hematuria if they involve in the urinary system.

The actual cause of hermaturia cannot be found in a few patients through repeated examination which is called "idiopathic hematuria". A causal attitude should not be adopted on this score.In some instances, urine becoming red in color is not a real hematuria. Eating a great amount of beet root, injecting or oral administrating some drug, such as pheonl red, rifampin, rhubarb root, etc. can make the urine red in color. The female should differentiate their urine contaminated by menstrual blood or blood from vagina or pile from the real hematuria.