2025 – PAGE 286 – HEMATOLOGY & ONCOLOGY

MICROCYTIC ANEMIA

MICROCYTIC ANEMIA DEFINITION

An MCV < 70 IS DEFINITELY CONSIDERED MICROCYTIC ANEMIA. The 70-80 range is NOT microcytic for a child less than 2 years of age.

IRON DEFICIENCY ANEMIA

Look for a LOW transferrin saturation, a HIGH RDW and LOW reticulocyte count to diagnose iron deficiency anemia. Also, if you are given a ferritin level < 15, that confirms the diagnosis. The lower limit of iron varies by age, but for infants 30 is the cutoff. For children, 55 is the cutoff.

• PEARLS: Transferrin transports iron, so if there’s no iron around, the transferrinsaturation will be low. The RDW (RBC Distribution Width) can also help you if it is HIGH because this suggests that there are old normal-sized RBCs mixed in with new MICROCYTIC ones (only helpful in the initial phase). You will NOT be asked to calculate the Mentzer index (MCV/RBC), but if you can it may help. An index > 12 = Iron Deficiency Anemia. An index < 11 = Thalassemia.
• PEARLS: WHOLE COW MILK (not formula) has LOW iron and may be a cause of SEVERE anemia if started in a child before the age of 1. Choose nutritional deficiency as the etiology, not bleeding (unless of course the stool guaiac is positive).
• PEARLS: Sorry if these are obvious, but viruses can cause marrow suppression and possibly a transient anemia. Don’t treat the anemia with iron. Keep in mind that some of the above lab values have a very high POSITIVE predictive value, but a LOW negative predictive value. So if a ferritin level is < 15, it is VERY helpful (high PPV). If it is normal or high (can be elevated as an acute phase reactant), then the result is “negative” or “normal,” and it doesn’t help you at all (low NPV).

(DOUBLE TAKE) ANEMIA OF CHRONIC DISEASE

Anemia of a chronic disease is a chronic inflammation that leads to a defect in the production of RBCs. There are plenty of building blocks, so the MCV is usually NORMAL, but it can be LOW NORMAL or only BORDERLINE LOW. This can be a normocytic or a slightly microcytic anemia. Also look for a low TIBC (Total Iron Binding Capacity). The TIBC measures the ability of transferrin to take on more iron. If the value is low, there’s plenty of iron around.

THALASSEMIAS

The thalassemias are autosomal recessive disorders, so parents who are carriers can have “traits.” As a reminder, normal adult hemoglobin (A1) is made up of 2 alpha chains and 2 beta chains. There are normally four genes controlling production of the 2 alpha chains and two genes controlling production of the two beta chains. Gene deletions (or defects) result in thalassemias, though a single gene deletion (or defect) does not usually result in a thalassemia.

ALPHA THALASSEMIA

Alpha thalassemia refers to a mutation in an alpha chain gene. The severity of the disease depends on the number of defective genes, from one to four. Patients with alpha thalassemia due to one (alpha thalassemia minima) or two (alpha thalassemia minor) gene defects are asymptomatic, while patients with three gene defects (Hemoglobin H disease) can have moderate to severe symptoms (hemolytic anemia, splenomegaly, bone changes). If all 4 genes are defective (Hemoglobin Barts), then the result is hydrops fetalis (not compatible with life).

PEARL: The only things you probably need to know for the exam are that alpha thalassemia can cause a microcytic anemia, it’s usually less severe than beta thalassemia, and it cannot be definitively diagnosed by hemoglobin electrophoresis (must do genetic testing). It is unlikely that you will be asked to name the types of alpha thalassemia on the exam, or that you would be asked to identify different types of hemoglobin, such as Hgb A1 = alpha-beta, Hgb S = alpha-beta (but with a defective beta due to Glu-Val), Hgb A2 = alpha-delta and Hgb F = alpha-gamma.