What indicator is known to increase in cases of iron deficiency?

Erythrocyte protoporphyrin levels are known to increase in cases of iron deficiency because it is a crucial component of hemoglobin, which requires iron for its synthesis. In the absence of adequate iron, the body continues to produce protoporphyrin but struggles to incorporate it into hemoglobin, leading to an accumulation of unutilized protoporphyrin within red blood cells. This accumulation serves as an indicator of inadequate iron supply for hemoglobin production, thus directly correlating to iron deficiency in the body.

In contrast, hemoglobin levels may remain normal until the deficiency becomes severe, and serum ferritin levels provide an indication of iron stores, which decreases in cases of iron deficiency. Serum transferrin concentrations can also fluctuate and typically increase when iron stores are low, but it does not reflect the actual deficiency state as clearly as erythrocyte protoporphyrin levels. Therefore, in the context of identifying iron deficiency specifically, monitoring erythrocyte protoporphyrin provides valuable insight into the body's iron status.