Getting tests, if you are in the US, isn't too hard. You just go to the Quest Diagnostics website and choose the part that is for physicians. There is a test center. You can look up what tests are available there. You'll have to choose the lab for your state, as the test codes and the tests vary. You want to write down the actual test name and test code for your state.
For example, if you lived in NY state and wanted to test aldosterone, you'd find this:
"Aldosterone, LC/MS/MS" with test code 17181X. You want the test code, not the CPT code.
There are quest diagnostics draw centers all over the USA. You can find one on their website.
So if your physician wants to test aldosterone, you can give them this info, they can write a prescription for the test, and you just bring it to quest and they'll draw it for you and send the results to your physician.
Sometimes, when I've wanted to explore something less conventional, and need to ask a physician for a test requisition, I find it is helpful if I do the legwork for them and figure out exactly what the test is. The physician may feel the test is entirely reasonable and interesting to run, but may not be aware of it. There are so many tests available now through quest and other labs that no doctor could be expected to know them all.
I do, however, find it surprising that an endocrinologist cannot figure out how to test aldosterone... In theory, all they have to do is write "aldosterone" on a prescription pad, give it to you, and you bring it to a lab that tests it. The code isn't really necessary but for more obscure tests it's helpful since w/o it, the phlebotomist must look up what the physician ordered and guess which test code to enter, and sometimes you get the wrong test (e.g. I've gotten the wrong vitamin D test sometimes, 25-OH D3 vs 1,25-OH D3 - very different tests used for very different purposes. Having codes also really speeds things up when getting your blood drawn.
All of this, of course, assumes your physician is willing to order the test. My point is not to tell you what tests to order - only that if you and your physician want to order a test for something, but the physician is unsure of how to do so, you can facilitate this process fairly easily.
You all probably know already that as ME patients we cannot just trust our docs to know what to do about everything. Unfortunately, they aren't trained for it in med school and their peers generally don't even believe it exists - so if you have a physician who is sufficiently understanding and willing to try to help you, cut them a break and do what you can to help them help you. The most important qualities in a good physician, imo, are open-mindedness, curiosity, critical thinking, compassion, and trust in the patient. I've had a lot of physicians look me in the eye and say "I don't know" - that's totally fine with me. I like that they are confident enough to admit it. No one knows everything. If they are willing to help you figure it out, that's huge right there.
Remember that docs don't have it as great as they used to - high patient load, low compensation, extreme pressure to see more patients per hour, endless paperwork created by the insurance companies, litigation or threat thereof (often frivolous), etc. If we want docs to try to see things from our point of view, then we should also be willing to try to see it from theirs.
Some docs just suck all around unfortunately, but many are really good, intelligent people who want to help if given the chance to do so. If the doc sucks, drop him/her and move on and find a better one. That's not the same as the doc not agreeing with you though - I don't think getting a yes-man (or woman) would be beneficial to our care. Ideally, the physician and patient form a relationship built on trust and work as a team to improve the patient's health. The good docs, and the good patients, understand this dynamic.