5 High Yield Hematology Pearls for Clinical Practice and the ABIM Board Exam

Hematology is a subject that comes up daily in clinical practice, and is a favorite on the ABIM Internal Medicine board exam. Evaluation of anemia, as well as some other hematologic disorders, is paramount for an internist to master. I will try and provide five evidence-based pearls in this post that will help physicians understand some important concepts and avoid common pitfalls in the recognition and treatment of such hematological disorders.


Pearl #1: Patients on iron supplementation SHOULD NOT have positive guaiac tests.
  • Studies in vitro show ferric iron (Fe3+) will give a positive guaiac reaction and ferrous iron (Fe2+) does not
  • Iron is digested in the ferrous form and carried in the blood in the ferric form
  • Patients on iron supplementation with positive guaiac require screening for identifying the source of gastrointestinal hemorrhage
  • Ferrous (Fe2+) iron does not cause positive guaiac tests in vivo
Pearl #2: The pentad of Thrombotic Thrombocytopenic Purpura (TTP) is not always present.
  • The pentad is: microangiopathic hemolytic anemia (MAHA), thrombocytopenia, renal abnormalities, neurologic abnormalities, and fever
  • Less than 50% of patients have the complete pentad
  • Measurement of ADAMTS13 activity is not required to make the diagnosis; the diagnosis is clinical
  • The gold standard treatment is plasma exchange and if not available you may use fresh frozen plasma as an alternative treatment
Pearl #3: Primary hemostasis disorders are a platelet dysfunction and secondary hemostasis disorders are a clotting factor disorder.
  • Primary hemostasis Disorders:
    1. A result of platelet function
    2. Immediate clotting
    3. Patients will have petechiae and purpura
    4. All will have elevated bleeding time (platelets don’t work) and normal PT/PTT (no problem with clotting factors)
  • Secondary hemostasis Disorders:
    1. A result of clotting factors
    2. Delayed clotting (help strengthen clots by fibrin formation)
    3. Patients will have hematomas and hemarthroses
    4. All will have normal bleeding time (platelets work fine) and abnormal PT (extrinsic pathway) and PTT (intrinsic pathway)
Pearl #4: Acute myelogenous leukemia (AML) type M3 has a good prognosis.
  • AML is the most common type of acute leukemia in adults
  • Typically M2 – M5 types are myeloperoxidase stain positive (Remember that PTU and micropolyangitis can also be positive)
  • Auer rods are pathognomonic for AML
  • Type M3 (promyelocytic) leukemia has t(15,17)
  • The treatment of choice is all-trans retinoic acid (ATRA)
  • The single most important prognostic factor in AML is cytogentetics: t(15;17) has a 70% 5 year survival and 33% relapse rate
Pearl #5: Anemia is the most common hematologic abnormality, so know it cold.
  • Iron deficiency anemia is the world’s most common cause of anemia
  • Iron deficiency anemia:
    1. Low iron, transferrin saturation, and ferritin
    2. Elevated TIBC
    3. Transferrin Receptor Index = transferrin receptor/Log Ferritin is the most sensitive assay for iron deficiency anemia (>2.0 = Iron Deficiency Anemia; <1.0 = Anemia of Chronic Disease)
    4. Treatment is PO iron → if no improvement after 6 weeks consider IV iron
    5. The earliest lab to check after starting iron replacement is the reticulocyte count (Begins to increase at about 5 to 7 days)
    6. Ascorbic acid (vitamin C) supplementation increases absorption of iron
    7. Most iron is absorbed in the duodenum
    8. Celiac sprue can cause iron deficiency anemia: Best test is tissue transglutaminase antibody or antiendomysial antibody; Tx is a gluten free diet; Can see dermatitis herpetiformis associated with this entity


As I have stated in my high yield pearls to pass the boards: “Most commons” are emphasized on the ABIM curriculum, so it is good to know these disease processes. Also, diseases that are increasing in incidence or have a high mortality associated with them are also high yield. Anemia (most common hematologic abnormality), AML (most common acute leukemia in adults), and Thrombotic Thrombocytopenic Purpura (high mortality) are 3 of the hematology pearls covered in this post. Best of luck as you are preparing for your ABIM board exam, and hopefully these pearls help you get a few more questions correct.


  1. George JN. How I Treat Patients With Thrombotic Thrombocytopenic Purpura: 2010. Blood 2010 Nov; 116 (20): 4060 – 9. PMID: 20686117
  2. Grimwalde D et al. The Importance of Diagnostic Cytogenetics on Outcome in AML: Analysis of 1,612 patients entered into the MRC AML 10 Trial. The Medical Research Council Adult and Children’s Leukemia Working Parties. Blood 1998 Oct; 92 (7): 2322 – 33. PMID: 9746770
  3. Konrad G et al. Are Medication Restrictions Before FOBT Necessary?: Practical Advice Based on a Systematic Review of the Literature. Can Fam Physician 2012 Sep; 58 (9): 939 – 48. PMID: 22972722
  4. McDonnell WM et al. Effect of Iron on the Guaiac Reaction. Gastroenterology. 1989 Jan; 96 (1): 74 – 8. PMID: 2909440
  5. Rimon E et al. Diagnosis of Iron Deficiency Anemia in the Elderly by Transferrin Receptor-Ferritin Index. Arch Intern Med 2002 Feb; 162 (4): 445 -9. PMID: 11863478

About Salim Rezaie

Dr. Rezaie completed his medical school training at Texas A&M Health Science Center, and followed that up with a combined Emergency Medicine/Internal Medicine residency at East Carolina University in Greenville, NC. Currently, he is an attending on the faculty of UTHSCSA in San Antonio, TX, where he focuses on medical education, social media as a tool for education (FOAMed), and building the bridges between internal medicine, critical care, and emergency medicine. Feel free to contact him on Twitter (@srrezaie) (@UTHSCSAPearls) about anything EM/IM! Salim Rezaie

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