What role do iron studies play in differentiating between iron deficiency anaemia and anaemia of chronic disease?

Role of iron studies in differentiating iron deficiency anaemia (IDA) and anaemia of chronic disease (ACD):

Iron studies are essential in distinguishing IDA from ACD by assessing iron status markers such as serum ferritin, transferrin saturation, and other specialized tests.

In IDA, serum ferritin is typically low, reflecting depleted iron stores, whereas in ACD, ferritin may be normal or elevated due to its role as an acute phase reactant.

Transferrin saturation is usually low in both conditions but is interpreted alongside ferritin and clinical context.

In people with chronic kidney disease (a common cause of ACD), NICE recommends not relying on transferrin saturation or serum ferritin alone to assess iron deficiency; instead, they advise using percentage of hypochromic red blood cells (% HRC), reticulocyte haemoglobin content (CHr), or a combination of transferrin saturation (<20%) and serum ferritin (<100 µg/L) to better differentiate iron deficiency from functional iron sequestration seen in ACD.

Furthermore, a good haemoglobin response to iron therapy (e.g., a rise of ≥10 g/L within 2 weeks) strongly suggests absolute iron deficiency even if iron studies are equivocal.