A 70-year-old woman has been in long-standing poor health, with severe diabetes mellitus and rheumatoid arthritis. Her physician notes that she appears pale and orders a hematocrit, which shows a result of 35%. Examination of the blood smear reveals a microcytic anemia. The physician is considering a differential diagnosis of iron deficiency anemia versus anemia of chronic disease. Which of the following laboratory determinations would be most helpful in distinguishing these conditions?
A. Erythrocyte:granulocyte ratio in bone marrow
B. Presence or absence of polychromatophilic target cells
C. Presence or absence of stippled erythrocytes
D. Serum ferritin
E. Serum iron
The Correct Answer is D. Serum ferritin
This is a common clinical scenario in real life.
Serum ferritin is markedly decreased in iron deficiency anemia and is normal to modestly elevated in anemia of chronic disease. This difference makes this test very useful in this setting. You should be aware that serum ferritin may behave like an acute phase reactant. Therefore, in an acute inflammatory situation, erythrocyte ferritin may be more reliable if serum ferritin is equivocal. Also, do not forget that iron deficiency anemia can complicate the anemia of chronic disease (e.g., gastrointestinal bleeding can complicate gastrointestinal cancers); in this situation, most physicians treat the apparent iron deficiency anemia and see to what degree the anemia corrects.
The erythrocyte:granulocyte ratio in bone marrow (choice A) is slightly decreased in both iron deficiency anemia and anemia of chronic disease, but may be markedly increased in sideroblastic anemias.
Polychromatophilic target cells (choice B) and stippled erythrocytes (choice C) are absent in both iron deficiency anemia and anemia of chronic disease, but may be present in sideroblastic anemias and other iron-utilization anemias.
Serum iron (choice E) is decreased in both iron deficiency anemia and anemia of chronic disease, but may be markedly increased in sideroblastic anemia.