Hello, Im An 18 Year Old Female, And I Recently

Hello, im an 18 year old female, and I recently went to get bloodwork done to test for low iron. I just got the results back today and they said that my iron levels weren't normal so they wanted to retest again, but they added a pregnancy screening? My question is why would they add the pregnancy test? The only reason I can think of is that I was in my menstrual cycle while I got my bloodwork. I am also taking birth control as well. Thanks