What is the best laboratory test to distinguish iron deficiency anemia from other types?

The serum ferritin level is the most appropriate laboratory test for distinguishing iron deficiency anemia from other types of anemia. Ferritin is a protein that stores iron in the body, and its level reflects the total iron reserves. In cases of iron deficiency anemia, ferritin levels are typically low because the body's stores of iron are depleted. This makes serum ferritin a specific marker for diagnosing iron deficiency.

While the mean corpuscular hemoglobin concentration and mean corpuscular volume can provide information about red blood cell characteristics, they do not specifically indicate the presence or absence of iron deficiency. Transferrin saturation can indicate how well iron is being transported, but it is not as definitive as serum ferritin regarding iron stores. Therefore, serum ferritin is the primary test used to confirm iron deficiency anemia and differentiate it from other types of anemia.