"anion gap" test is irrelevant

Before giving me my MS drug last week, the nurse drew blood for tests. The automated test result that I received within the hour included a flag for a low anion gap, whatever that meant. Googling told me that it's related to blood pH, but nothing about why they did that test or what it meant in my case.

I emailed the doctor this morning, and got a quick reply, saying I should ignore it, because that test is only relevant to sick hospitalized patients. I thanked him, and am not going to pursue the question of why that test was even done, or why I've been given it a few times before. (MyChart offered a graph of past test results.)