Hematospermia (blood in sperm) is perceived in medicine as a symptom of little significance — unless symptoms occur longer than one month.
The cause is usually inflammation as a result of infections: by Chlamydia, HSV (Herpes Simplex Virus), CMV (Cytomegalovirus), Trichomoniasis, prostatitis, epididymitis, urethritis, Gonorrhea, or calculis similar to kidney stones in seminal vesicles or prostate. Other causes are: physical trauma, testicular trauma, excessively rigorous sexual activity, prolonged sexual abstinence.
Symptoms include burning urination, abdominal pain, discharge, inflammation of one testicle/scrotum, abdominal and back pain, fatigue, weight loss, swelling or tenderness in groin.
Labs which may be done are: PT/PTT, INR, CBC, liver function tests, PSA, Urinalysis and Culture, semen culture, cystoscopy, ultrasound of the prostate and seminal vesicles, and an MRI.
Hematospermia usually resolves on its own without treatment and is self limiting. One half of the time the cause is never found.