Retrograde Analysis

Aspermia – Retrograde Flow of Semen

If no ejaculate is produced following masturbation, semen may have flowed back into the urinary bladder. To confirm “aspermia”, the initial fraction of the voided urine following such a “dry” ejaculation should be checked for sperm. 

Reference:

Semen Collection and Processing Methods BY R.S. Jeyendran.
Cambridge University Press, Cambridge, UK.