If you're where I did fellowship, the answer would inevitably be "Call Endocrine". I swear, I was called by the ED maybe a dozen times in all of fellowship, and all but 2 were for thyrotoxicosis that did not meet criteria for storm. The same held for my cofellows - the ER was perfectly happy managing all kinds of suspected Endocrine issues (suspected adrenal insufficiency was a perennial favorite), almost always in a reasonable fashion, but for some reason would often call for thyrotoxicosis.
That said, the answer from our service more or less never changed - newly diagnosed thyrotoxicosis in a non-pregnant adult who isn't in storm can be treated symptomatically (beta blockade) but until you've ruled out thyroiditis as an etiology, we typically would prefer not to muddy the picture with thionamide therapy (methimazole/PTU). Ideally, in my perfect world, you'd make sure you had a full set of TFTs (TSH, Free T4, either a total or free T3 depending on which is more reliable in your lab - and either is fine really) plus a TSH receptor antibody or thyroid stimulating immunoglobulin (both TRAB and TSI are fine in my book, some providers quibble over which they prefer) and an urgent referral to me.
The antibody testing (if positive) saves me/the patient time/effort, but it's obviously not something that you need to wait to result in the ED - it's just helpful for when the patient follows up.
