Rhade has heard about Dr. McCoy from Captain Kirk, and a doctor with starship experience has it's appeal. That's what eventually leads Rhade to Hellsing, and he requests the location of his office and heads back to it.

At least he has a very specific question that he can ask. His blunted boneblades are still very uncomfortable and agitating, and having been caught without them by the Candlelighters had been extremely compromising. Not to mention that it made him feel half of what he was.

He's in his High Guard uniform as he knocks on the door, posture ramrod straight and overly formal, and he waits with his hands clasped behind his back and his chin slightly raised.