Final answer:
The most sensitive test for diagnosing iron-deficiency anemia is serum ferritin, as it reflects the body's iron stores and is a better indicator compared to serum iron.
Step-by-step explanation:
The most sensitive test for diagnosing iron-deficiency anemia is serum ferritin. Ferritin serum levels serve as a direct indicator of the iron stores in the body, since ferritin is the storage form of iron. When the body's iron levels fall, serum ferritin levels also drop, making it a more sensitive marker for iron-deficiency anemia compared to serum iron levels, which can be affected by various factors and might not accurately reflect iron stores. While both serum iron and ferritin can provide information about iron status, abnormal iron metabolism often calls for examining ferritin levels to get a clearer understanding of a patient's iron reserves.