Internalize Info of the Week: Hemolytic Anemia Laboratory Evaluation

A couple of days late for the info of the week, but I still think this is worth posting. I have been moving around and haven't had access to a computer for a few days.

This week I was pimped on the laboratory findings that you see in anemia, specifically hemolytic anemia. All anemias are characterized by a decrease in red blood cells (RBCs). For men, this is a hemoglobin < 13.5 g/dL and a hematocrit < 41%. For women, this is a hemoglobin < 12 g/dL and a hematocrit of < 36%.

For hemolytic anemia, there are several characteristic lab findings. The reticulocyte count will be increased with a reticulocyte index > 2%, meaning the patient’s bone marrow is working properly and is producing immature RBCs. Haptoglobin (a protein that binds free hemoglobin in the serum) will be decreased, because it is now bound to the hemoglobin and is not measured. Lactate dehydrogenase (LDH) will be increased, because this enzyme is released into the serum when the RBCs are hemolyzed. Also, indirect bilirubin will be increased because this product is created as hemoglobin is broken down and there is too much for the liver to conjugate. On a peripheral blood smear, schistocytes are seen which are RBC fragments left after the cell breaks apart. Additionally, the direct Coombs’ test is used to evaluate hemolytic anemia. If it is positive, it narrows the differential to autoimmune hemolytic anemias.

To summarize the laboratory findings: reticulocyte count, LDH, and indirect bilirubin are all increased, while haptoglobin is decreased.

This is just a general laboratory evaluation to determine if the anemia is hemolytic. Other specific causes of hemolytic anemia have their own characteristic lab findings that are not discussed above.

Sources:
"Anemia." Pocket Medicine. Ed. Marc S. Sabatine. Fourth ed. Philadelphia: Lippincott Williams & Wilkins, 2011. 5-1, 5-4. Print.
Vorvick, Linda J., James R. Mason, and David Zieve. "Haptoglobin: MedlinePlus Medical Encyclopedia." National Library of Medicine - National Institutes of Health. 21 Mar. 2010. Web. 14 Nov. 2011. <http://www.nlm.nih.gov/medlineplus/ency/article/003634.htm>.
Vorvick, Linda J., James R. Mason, and David Zieve. "Lactate Dehydrogenase Test: MedlinePlus Medical Encyclopedia." National Library of Medicine - National Institutes of Health. 21 Mar. 2010. Web. 14 Nov. 2011. <http://www.nlm.nih.gov/medlineplus/ency/article/003471.htm>.
Dugdale, III, David C., and David Zieve. "Bilirubin - Blood: MedlinePlus Medical Encyclopedia." National Library of Medicine - National Institutes of Health. 20 Feb. 2011. Web. 14 Nov. 2011. <http://www.nlm.nih.gov/medlineplus/ency/article/003479.htm>.