Ferritin levels above 40 µg/L are recommended for hair growth and trichologists advise a level of over 70µg/L.
Regardless of your individual result, other important parameters need to be investigated such as liver function, and vitamins and minerals (such as zinc and B9). Diagnosing the cause of hair loss can be difficult with blood tests as the results can often be misleading.
If you are concerned about your hair loss see a doctor or a hair loss specialist that can advise you on the next steps. If you are concerened about hair loss due to low iron, include plenty of iron rich food in your diet such as red meat and dark green vegetables. If you do you are aware you have an iron deficiency, this may need to corrected with iron supplements over a period of time, though it is likely that iron supplementation alone will not correct the problem.