if a blodo test has come back with a reasult suggesting that something has been left behind, then you owe it to the horse to see things through and go ahead nd see what is going on and having things removed. This may help his behaviour however there is no guarentee.
My gelding acted very riggy when i got him, he was mounting mares, he was getting aroused, was fighting with the geldings. calling to and chatting up the mares, and things where progressing to other areas liek his ridden work. I got the vet to do a blood test , however in my case my boys bloods came back normal, in fact even low for a gelding, so nothing retained.
In my geldings case he was a stallion till the age of 6-7 and ran with mares. So in his case it is a learned behaviour, somethign i can not change. In many ways had he had somethign left behind it woudl of at least been a chance to try and change his behaviour.
However it is now down to carefull management, he will happily go out with geldings as long as there are no mares near by. I have provided him with a consistant companion, one he is stabled near and is turned out with. This has helped him a lot.
I have to be firm with him, however i dont use it as an excuse. Being a stallion is natural for a horse remember , it isnt an illness. There is no reason for any horse tobe turned out alone, If i was t turn my gleding out alone he woudl thret so much, he woudl probably injure himself tryign toget to company.
You have to look at your horses situation, look for triggers, anbd deal with things gradually. however having what ever is left behind, removed coudl well help you.
I knwo it isnt cheap , however i was prepared to do this for my gelding.