Hematology is a topic that comes up daily in clinical practice, and is a favorite in the ABIM Internal Medicine board exam. Evaluation of anemia, as well as some other hematologic disorders, is critical for an internist to master. I will try to provide five evidence-based gems in this post that will help clinicians understand some important concepts and avoid common mistakes in the recognition and treatment of such hematologic disorders.
Pearl #1: Patients taking iron supplements SHOULD NOT test positive for guaiac.
- In vitro studies show ferric iron (Fe3+) will give a positive reaction of guaiac and ferrous iron (Fe2+) It is not
- Iron is digested in the ferrous form and is transported in the blood in the ferric form.
- Guaiac-positive patients receiving iron supplementation require examination to identify the source of gastrointestinal bleeding
- Ferrous (Fe2+) iron does not cause positive guaiac tests in vivo
Pearl #2: The thrombotic thrombocytopenic purpura (TTP) pentad is not always present.
- The pentad is: microangiopathic hemolytic anemia (MAHA), thrombocytopenia, renal abnormalities, neurological abnormalities, and fever.
- Less than 50% of patients have the full 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 this is not available you can use fresh frozen plasma as an alternative treatment.
Pearl #3: Primary disorders of hemostasis are platelet dysfunction and secondary disorders of hemostasis are coagulation factor disorder.
- Primary disorders of hemostasis:
- A result of platelet function.
- Immediate coagulation
- Patients will have petechiae and purpura.
- Everyone will have an elevated bleeding time (platelets not working) and a normal PT/PTT (no problem with clotting factors)
- Secondary disorders of hemostasis:
- result of coagulation factors
- Coagulation delay (helps to strengthen clots by forming fibrin)
- Patients will have bruises and hemarthroses.
- Everyone will have a normal bleeding time (platelets are working fine) and abnormal PT (extrinsic pathway) and PTT (intrinsic pathway).
Pearl #4: M3 type acute myelogenous leukemia (AML) has a good prognosis.
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AML is the most common type of acute leukemia in adults.
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Types M2 – M5 are usually positive for myeloperoxidase staining (remember that PTU and micropolyangiitis can also be positive)
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Auer rods are pathognomonic of AML
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Leukemia type M3 (promyelocytic) has t(15,17)
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The treatment of choice is all-trans retinoic acid (ATRA).
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The most important prognostic factor in AML is cytogenetics: t(15;17) has a 5-year survival of 70% and a relapse rate of 33%.
Pearl #5: Anemia is the most common hematologic abnormality, so get to know it.
- Iron deficiency anemia is the most common cause of anemia in the world.
- Iron deficiency anemia:
- Low iron level, transferrin saturation and ferritin
- elevated TIBC
- 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)
- Treatment is PO iron → if no improvement after 6 weeks consider IV iron
- The earliest lab to check after starting iron replacement is the reticulocyte count (begins to rise around 5-7 days)
- Ascorbic acid (vitamin C) supplementation increases iron absorption
- Most of the iron is absorbed in the duodenum.
- Celiac disease can cause iron deficiency anemia: the best test is anti-tissue transglutaminase antibody or anti-endomysial antibody; Tx is a gluten-free diet; Dermatitis herpetiformis associated with this entity can be seen
As I said in my high-achieving pearls for passing boards: “Most commons” are emphasized in the ABIM curriculum, so these disease processes are good to know. Furthermore, diseases that are increasing in incidence or have high mortality associated with them are also high yielders. Anemia (the most common hematologic abnormality), AML (the most common acute leukemia in adults), and thrombotic thrombocytopenic purpura (high mortality) are 3 of the hematologic pearls discussed in this publication. Best of luck as you prepare for your ABIM board examand I hope that these pearls will help you answer some questions more correctly.