The serum ferritin is used more often than bone marrow or liver biopsies to assess iron stores because it is:

a. A more direct measurement
b. More accurate
c. More precise
d. Less invasive

ANS: D
The measurement of ferritin is performed on a serum sample; therefore it requires nothing more than a venipuncture to obtain a blood specimen. It is proportional to the iron in stores, but it is not a more direct measurement. In fact, a bone marrow biopsy followed by staining with Prussian blue to assess iron stores (in the form of hemosiderin) is perhaps the best measurement of iron stores that are readily available for use in hemoglobin synthesis. This is much more invasive.