Microcytic Anemia

Ddx for a microcytic anemia:

• Iron deficiency anemia: see below
• Anemia of chronic disease: TIBC and Fe should be low, ferritin nl or high (soluble transferin receptor can help distinguish—high in Fe def anemia, low in ACD)
• Sideroblastic anemia: ringed sideroblasts on smear, can be congenital, acquired causes are usually drug induced (including copper deficiency, zinc toxicity, etoh) or due to MDS
• Thalassemia: iron and ferritin should be nl, retic index is high, HgA2 increased

Iron Deficiency anemia:

• Lab findings include: microcytosis, a low MCV with a reduced iron content (hypochromia and low MCH), a low serum iron, an increased total iron binding capacity (transferrin), and a reduced transferrin saturation (ie, a lower than normal ratio of serum iron to total iron binding capacity, expressed as a percentage).
• Ferritin is the test with the highest sensitivity and specificity for the diagnosis of iron deficiency; a serum ferritin concentration of < 15 ng/mL has a sens of 59% and a spec of 99 % for iron deficiency
• Transferrin: ferritin index: <1 usually anemia of chronic disease, >2 suggests IDA
• This is NOT a diagnosis by itself, it must include an appropriate workup for causes of blood loss, malabsorption, hemolysis etc. 
• In women….
• A history of menorrhagia or pregnancy is likely in a premenopausal woman, but there needs to be clear history to support it, and appropriate follow-up (iron deficiency should resolve within several weeks on iron supplementation and OCPs, if appropriate)
• The generally lower value for iron stores in adult women reflects the composite effect of menstrual losses (approximately 1 mg of iron loss per day), lower caloric intake, use of supplemental iron, and iron losses associated with pregnancy and lactation (about 1000 mg each for pregnancy, delivery, and nursing).

 

Ddx of iron deficiency anemia:

· Blood Loss:

o overt (hemoptysis, menorrhagia, melena, hematemesis etc.)

o or occult (in men, usually GI blood loss; in women, including underestimating menorrhagia, blood loss during delivery, pregnancy, lactation)

· Decreased iron absorption: relatively uncommon cause of iron deficiency

oatrophic gastritis, Helicobacter pylori gastritis, celiac disease, gastric bypass

·Other causes:

o intravascular hemolysis (hemoglobinuria and hemosiderinuria can lead to significant urinary iron losses)

o pulmonary hemosiderosis

o ESRD patients receiving erythropoietin without sufficient iron repletion

(see attached review article in Blood on Fe Def anemia, from some of our own Stanford hematopathologists)

Reticulocyte count

· Normal reticulocyte percentage is 0.5 to 1.5%

· Assuming the bone marrow is normal and there are sufficient erythropoeitin and iron stores, acute anemia (ie. hemolysis or blood loss) should increase the retic % to 4-6%

· The absolute reticulocyte count (or reticulocyte index) is reflective of the underlying degree of anemia and must be corrected based on the hematocrit

· The corrected reticulocyte count is equal to the patient's Hct divided by 45 and multiplied by the percentage of reticulocytes. RI= retic % x Hct/45

· (In general, a reticulocyte index >2=appropriate BM compensation.

· Remember that early reticulocytes are bigger than mature red cells, so a high reticulocyte count elevates the MCV.

(Victoria Kelly MD, 4/6/11)