Expert review by Sioban Keel, MD (Hematology)
- Construct a framework for the evaluation of anemia.
- Differentiate between immune-mediated and non-immune causes of hemolysis.
- Interpret reticulocyte index, hemolysis labs, DAT, and peripheral blood smear results to aid in the diagnosis of anemia.
Estimated time: 45-50 minutes. This is an extensive differential and overall retention may be better splitting them up into two separate talks:
- Underproduction anemia
- Overproduction anemia with cases.
Plan to spend at least 30-60 minutes preparing for this talk by using the Interactive Board for Learning/Preparing and clicking through the graphics animations to become familiar with the flow and content of the talk. Print out copies of the Learner’s Handout so learners can take notes as you expand on the pathophysiology and management. The first page of the handout and is a blank schematic that learners can fill in as you go through the evaluation.
Begin with reviewing the objectives for the session. We recommend progressing in order, though this gives you the flexibility of doing more focused teaching. All clickable elements are indicated by a cursor icon and shading around the button. Some elements can be clicked more than once. The cursor will disappear when all clickable elements are completed. A toolbox will appear next to key tests used in the evaluation of anemia.
- Slide 1 (Underproduction) – The first step in the evaluation of acute anemia is differentiating between underproduction (problem with the bone marrow) and overproduction. The reticulocyte index (click on this for how to calculate and more information) can help differentiate between these categories. In the hospital, an acute drop in hemoglobin/hematocrit may also be from large fluid shifts/hemodilution, and this will not be associated with a derangement in reticulocyte index. Of note, the reticulocyte index may be falsely low/normal if there is a concurrent underproduction process.
- Within underproduction, MCV can be further used to differentiate between macrocytic (MCV > 100), normocytic (MCV 80-100) and microcytic causes (MCV < 80). Some processes may not always necessarily fall into one category. For example, primary bone marrow pathologies can be macrocytic or normocytic. Anemia of chronic disease and iron deficiency anemia (especially in early stages) can be both normocytic or microcytic.
- Click on “are other cell lines involved” to help differentiate between some of the causes of macrocytic/normocytic anemia.
- Click on “How to differentiate between microcytic causes” to learn how iron studies help differentiate between anemia of chronic disease, iron deficiency anemia, and thalassemias.
- Bonus: Other markers of RBC morphology can help differentiate between causes. For example, the RDW (RBC distribution width) describes the uniformity of RBC sizes. An increased RDW suggests multiple differing sizes of RBCs which may indicate a mixed process (e.g., concurrent microcytic or macrocytic process). This can also be seen in early iron deficiency.
- Slide 2 (Overproduction) – Overproduction can be related to blood loss or destruction (hemolysis). Identify hemolysis with hemolysis labs (click on this tab to reveal tests). Once there is an indication of hemolysis, a direct Coombs test, or DAT, can help differentiate between immune vs. nonimmune hemolysis. A DAT detects antibodies against RBCs.
- Immune mediated hemolysis can be further split into “warm” and “cold” types. Click on each of these to learn more about them. A peripheral blood smear can be helpful as they will show spherocytes. Spherocytes are formed when the spleen removes parts of the RBC membrane that are bound by antibodies.
- Slide 3 (Non-immune hemolysis) – Non-immune hemolysis can be further split into fragmentation hemolysis (by the presence of schistocytes) and non-fragmentation hemolysis.
- Fragmentation hemolysis or microangiopathic hemolytic anemias are characterized by the presence of schistocytes (or fragmented RBCs). When there is concurrent thrombocytopenia, this should raise suspicion for a thrombotic microangiopathy (TMA), either primary or secondary). Schistocytes can also be seen in other disease processes. Challenge your learners to guess these before clicking to reveal the etiologies.
- Non-fragmentation, non-immune hemolysis can be further divided into pathologies that are intrinsic to the RBC or extrinsic to the RBC.
- Intrinsic causes can be a disorder of RBC membrane, RBC metabolism, or hemoglobinopathies. A peripheral blood smear and specialized testing can help differentiate between these causes.
- Extrinsic causes include 1) liver disease or hypersplenism 2) infections, which can cause direct injury to RBCs or result in toxin mediated damage and 3) medications that result in oxidative stress
- Cases – There are a total of 3 cases. After reading through the stem, have your learners request work-up and click on the corresponding section. Not all tests are needed in every case.
Use for self-directed learning and for preparing to present
Use for Presenting – there is less text and fewer pop-ups
Take Home Points
- The reticulocyte index, hemolysis labs, DAT, and peripheral blood smear can help differentiate between causes of anemia.
- Causes of underproduction can be further differentiated by the MCV into macrocytic, normocytic and microcytic etiologies.
- Hemolysis is further differentiated by the DAT and peripheral blood smear which can help identify autoimmune hemolytic anemia and microangiopathic hemolytic anemia (fragmentation hemolysis).
- Packman, CH. The Clinical Pictures of Autoimmune Hemolytic Anemia. Transfus Med Hemother. 2015. 42 (5):317-325.
- Image from Werner EJ & Villella, AD. Sideroblastic Anemias: Diagnosis and management. In Nonmalignant Hematology. Pp 125-135.
- Image fromhttps://imagebank.hematology.org/image/61458/rouleaux-in-a-peripheral-smear-multiple-myeloma
- Image from Kawakami, D. Massive Hemolysis due to Clostridium perfringens infection. Intensive Care Medicine. 2020. 46, 122. https://doi.org/10.1007/s00134-019-05739-2