Once there is low Hgb/Hct, what is the key lab to define iron deficiency anemia?

To accurately define iron deficiency anemia once low hemoglobin (Hgb) and hematocrit (Hct) levels are identified, ferritin is the key lab parameter. Ferritin reflects the body's iron stores and is typically low in cases of iron deficiency anemia.

While MCV (mean corpuscular volume) provides information about the size of red blood cells and can suggest microcytic anemia—which often occurs in iron deficiency—it does not directly indicate the iron status of an individual. MCV changes can be seen in various types of anemia and are not specific to iron deficiency alone.

Transferrin, another option, measures the protein that binds and transports iron but can be influenced by factors such as inflammation and nutritional status, making it less reliable as a definitive indicator of iron deficiency.

Mean corpuscular hemoglobin (MCH) gives information regarding the average amount of hemoglobin per red blood cell but, similar to MCV, does not serve as a direct marker for iron stores.

Therefore, ferritin is the most effective lab test for diagnosing iron deficiency anemia, as it specifically reflects iron availability in the body.