What are the reasons of having bloood in urine?

Many. 1% of people have it naturally due to thin membranes in the kindey filters. If it's new, we need to rule out tumors first; the host of causes also ranges from vigorous exercise to a hidden kidney stone. A physician should manage the workup. Good luck. Many people metabolize beets to produce a red urine which can give a scare.
Many causes. There are numerous causes of hematuria--the serious ones are kidney and bladder cancers. Other possibilities are stones, urinary infections, benign prostate enlargement, etc. For a nice video answer, see the following link: http://www.Youtube.Com/watch?V=0mfuntdwwv8.