Hello - thanks for asking you question.
Blood in the semen is known as hematospermia. There are a variety of causes, including any prostate infection or disease, cancer, or infection. It is possible that the blood can be from the kidney stone you passed, or a new kidney stone.
However, before attributing it to this, you should have it re-evaluated fully. Tests for infection (i.e. a urinalysis) and STDs should be considered. The imagining test of choice would be a transrectal ultrasound to evaluate structural abnormalities of the prostate gland, seminal vescicles, spermatic cord. MRI of the prostate can also be considered as a second line test.
If negative, a repeat cystoscopy should be considered.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.