Hi, thanks for your question. I quite understand your concerns. Your tests have helped exclude some of the common causes of blood in the semen; infection in the genital tract, prostatitis, prostatic cancer, and urinary tract infection. However, i need to re-assure you that blood in semen is usually benign and resolves on its own. However, other causes should be excluded if it becomes recurrent. These other causes include bladder cancer, urethral polyp, obstruction of the ejaculatory duct, cysts in the genital tract, and genital stones. Urethrocystoscopy can detect these anomalies. It involves using a flexible tube with a camera at the end to course through the urethra to the bladder. This procedure is done by a urologist, and you would need to see one if this symptom recurs. I hope i have answered your question. Best wishes.