<prompt> Most sensitive marker for iron deficiency anemia is?Increase in iron binding capacityDecrease in serum ferritin levelDecrease in serum iron levelIncreased serum free transferrin  <response>: Ans. is b i.e., Decrease in serum ferritin o In iron deficiency anemia the first change is decrease in iron storeso The decrease in iron stores is demonstrated by decreased serum ferritin levelo A low serum ferritin is the most sensitive lab test for iron deficiency anemia.Features of iron deficiency anemia are :-1 Perpheral blood picture There is microcytic hypochromic anemia microcytosis precedes hypochromia. Other features include:A. Poikilocytosis in the form of pencil cells small, elongated red cellsB. Target cellsC. Ring pessary cells central pallor occupies whole cell and only peripheral rim of hemoglobin is seen.D. There is decrease in MCV, MCH and MCHC. RDW is increased. There may be thrombocytosis.2 Bone marrow features Bone marrow is hypercellular with erythroid hyperplasia : There is depleted bone marrow iron which is detected by prussian blue staining of bone marrow aspirates. Bone marrow iron decreases earlier than serum iron.3 Various indicesA. Decreased: Serum ferritin earliest normal is 30-400 gdl, iron normal 50-170 ?gdl, percentage saturation transferrin saturation normal is 33, and bone marrow iron store.B. Increased: Total iron binding capacity TIBC, serum transferrin free transferrin, red cell free protoporphyrin, and hepacidin level. 