Hematology
7. What are reticulocytes? Why is a reticulocyte count routinely ordered in an anemia
work-up?
Reticulocytes are immature red blood cells. If their count is abnormally decreased in the setting
of anemia, the marrow is not responding properly and is the problem. A high reticulocyte count
should make you think of hemolysis or blood loss as the cause (the marrow is responding prop-
erly and is not the problem).
8. Which test comes next?
At this point, it depends. If you have a complete history and results of the other three tests,
most possibilities will be eliminated and you can order a confirmatory test. If the answer is still
not clear, consider a bone marrow biopsy. For the Step 2 exam biopsy is unlikely to be necessary
unless malignancy is the cause of the anemia.
9. What are the classic causes of microcytic, normocytic, and macrocytic anemia? Which
of these tends to have an inappropriately low reticulocyte count?
Microcytic Normocytic
With normal or elevated reticulocyte count With normal or elevated reticulocyte count
Thalassemia/hemoglobinopathy Acute blood loss
(e.g., sickle cell disease) Hemolytic (multiple causes)
Medications (antibody-causing)
With low reticulocyte count With low reticulocyte count
Lead poisoning Cancer/dysplasia (e.g., myelophthisic,
Sideroblastic anemia acute leukemia)
Anemia of chronic disease (some cases) Anemia of chronic disease (some cases)
Iron deficiency Aplastic anemia/medications causing
bone marrow suppression
Endocrine failure (thyroid, pituitary)
Renal failure
Macrocytic (all types have low reticulocyte count)
Folate deficiency Cirrhosis, liver disease
Vitamin B12 deficiency Alcohol abuse (interferes with folate use)
Medications (methotrexate, phenytoin)
10. What clues point to hemolysis as the cause for anemia?
• Elevated lactate dehydrogenase (LDH)
• Elevated bilirubin (unconjugated as well as conjugated if the liver is functioning)
• Jaundice
• Low or absent haptoglobin (intravascular hemolysis only)
• Urobilinogen, bilirubin, and hemoglobin in urine (only conjugated bilirubin shows up in
the urine, and hemoglobin shows up in the urine only when haptoglobin has been satu-
rated, as in brisk intravascular hemolysis)
• Pigmented gallstones or history of cholecystectomy (usually at a young age)
11. What is the most common cause of anemia in the U.S.?
Iron deficiency anemia.
12. Why do people get iron deficiency?
Iron deficiency is common in women of reproductive age because of menstrual blood loss.
In all patients over age 40 (men and especially postmenopausal women), it is important to rule
out colon cancer as a cause of chronic, asymptomatic blood loss. Increased requirements also
may lead to iron deficiency in children and pregnant or breast-feeding women. Give iron sup-
plements or iron-containing formula to all infants except full-term infants who are exclusively
breast-fed. Giving cow's milk before 1 year of age may lead to anemia by causing GI bleeding.
