On my first round of HT had to do this on my own as my uro did not believe it was necessary. My T level never went below 40 on the first round and my uro said 50 was the expectation. There were other references that noted 20 as the benchmark for "castrate level". I also had my DHT tested but uro again said it was not significant. He was not a fan of combined ADT.
On the second round I had the testing done on my own with my GP. This time it went as low as 13. I did not test the DHT.
Neither test is that expensive if you decide to do it on your own. I did it for my own peace of mind that the drugs were working although the side effects told me they were.