My trichologist thinks it's fine to retest every 3 months. After taking iron for roughly 3 weeks, i shed roughly 20 strands more on shower day. And after 4 weeks, the shedding went back down and even decreased slightly compared to the past 4 months. My trich said HL usually happens roughly 3 months after the trigger so i guess that 20 more could be due to my first blood work and period right after it. My ferritin is 22 in February. It could be lower before then as I suffered from really bad symptoms of low iron and low vitamin D for 5 months before February. One of my male friends who is a nurse was like it;s just blood test, it's not like you are donating blood every 3 months. I was like, hello? You are talking to a GIRL who has low ferritin!