True or False: A low serum ferritin is diagnostic of iron deficiency.

A low serum ferritin level is commonly understood as an indicator of iron deficiency. Ferritin is a protein that stores iron in the body, and its serum levels reflect the total iron stores. When iron stores are depleted, serum ferritin levels decline, making it a crucial marker for diagnosing iron deficiency anemia.

While a low ferritin level is a strong indicator of iron deficiency, it is important to note that an isolated low ferritin level should be interpreted in the context of the overall clinical picture and may not be definitive on its own. For instance, in certain conditions such as inflammation or chronic disease, ferritin levels can be misleading since they may remain normal or elevated despite low iron stores.

Thus, while a low serum ferritin is indeed a key diagnostic criterion for iron deficiency, it should be supplemented with other laboratory values such as serum iron, total iron-binding capacity, and transferrin saturation for a comprehensive assessment.