I believe the iron test shows what is carried in your blood...and Ferritin shows how much iron you are storing.
Your body first uses what is stored and when that is used up...the iron in your blood will start to deplete.
(That is my understanding)
Are you supplementing iron?
My son had that low Ferritin - when he was undiagnosed for Celiac disease.
For parathyroid - this is the site I used. There is a chart where you can see where you can check your calcium and parathyroid hormone levels on a chart. Many Dr.'s don't have it right when they look at the labs.
www.parathyroid.com/about-parathyroid.htm