4.2 Hematologic
Key Takeaways
The Hematologic System is 4% of the PANRE blueprint; the highest-yield skill is classifying anemia by mean corpuscular volume into microcytic, normocytic, and macrocytic categories
Iron deficiency is the most common cause of microcytic anemia and typically shows low ferritin, low serum iron, and high total iron-binding capacity
Vitamin B12 and folate deficiency cause macrocytic megaloblastic anemia; B12 deficiency can also cause neurologic deficits that folate does not
Warfarin is monitored with the INR, while heparin-class and direct oral anticoagulants have distinct monitoring and reversal considerations
Acute leukemia presents with rapid marrow failure (anemia, infection, bleeding), whereas Hodgkin lymphoma is classically associated with Reed-Sternberg cells
The Hematologic System is 4% of the NCCPA PANRE blueprint. Although it is a lower-weight section, the topics overlap heavily with cardiovascular, infectious disease, and oncology questions, so the return on review is high. The recurring testable skill is interpreting a complete blood count (CBC) and coagulation studies, then choosing the next diagnostic or management step.
Classifying Anemia
The mean corpuscular volume (MCV) is the anchor. Classify first, then work up.
| MCV Category | Common Causes | Key Labs |
|---|---|---|
| Microcytic (low MCV) | Iron deficiency, thalassemia, anemia of chronic disease (can be normocytic) | Ferritin, iron studies |
| Normocytic (normal MCV) | Acute blood loss, anemia of chronic disease, hemolysis, renal disease | Reticulocyte count, hemolysis labs |
| Macrocytic (high MCV) | Vitamin B12 deficiency, folate deficiency, alcohol use, hypothyroidism | B12, folate, peripheral smear |
Iron Deficiency vs Anemia of Chronic Disease
Iron deficiency anemia is the most common anemia worldwide. It shows low ferritin, low serum iron, and high total iron-binding capacity (TIBC). In adults, new iron deficiency without an obvious source raises concern for occult gastrointestinal blood loss. Anemia of chronic disease typically shows normal or high ferritin (an acute-phase reactant) with low TIBC.
Macrocytic Anemia
Vitamin B12 and folate deficiency cause megaloblastic macrocytic anemia, often with hypersegmented neutrophils on smear. A critical distinction: B12 deficiency can cause neurologic findings (peripheral neuropathy, subacute combined degeneration); folate deficiency does not. Replacing folate alone in true B12 deficiency can mask the anemia while neurologic damage progresses.
Bleeding and Clotting Disorders
Use the coagulation panel to localize the defect.
| Finding | Suggests |
|---|---|
| Isolated prolonged PT/INR | Often warfarin effect or vitamin K-dependent factor issue |
| Isolated prolonged aPTT | Heparin effect, hemophilia, or factor deficiency in that pathway |
| Low platelets | Thrombocytopenia (ITP, drug-induced, marrow disease, consumption) |
| Prolonged PT and aPTT with low platelets and low fibrinogen | Disseminated intravascular coagulation (DIC) |
- Immune thrombocytopenia (ITP) is isolated low platelets without another explanation.
- Von Willebrand disease is the most common inherited bleeding disorder.
- Hemophilia A and B are X-linked factor deficiencies causing deep tissue and joint bleeding.
- Venous thromboembolism (VTE): deep vein thrombosis and pulmonary embolism are the clotting-side counterpart and are managed with anticoagulation.
Anticoagulation
| Agent Class | Example | Monitoring | Reversal Concept |
|---|---|---|---|
| Vitamin K antagonist | Warfarin | INR | Vitamin K; clotting factors for serious bleeding |
| Unfractionated heparin | Heparin | aPTT | Protamine |
| Low-molecular-weight heparin | Enoxaparin | Usually none routinely | Partial protamine effect |
| Direct oral anticoagulant (DOAC) | Apixaban, rivaroxaban, dabigatran | Not routinely monitored | Specific reversal agents exist for some |
Exam items often test that warfarin is monitored with the INR and interacts with diet and many drugs, while heparin-class agents are parenteral with faster onset.
Leukemias and Lymphomas Overview
- Acute leukemia (acute lymphoblastic or acute myeloid) causes rapid bone marrow failure: anemia, infection from neutropenia, and bleeding from thrombocytopenia.
- Chronic leukemia (chronic lymphocytic or chronic myeloid) is often more indolent and may be found incidentally.
- Hodgkin lymphoma is classically associated with Reed-Sternberg cells and can present with painless lymphadenopathy and B symptoms (fever, night sweats, weight loss).
- Non-Hodgkin lymphoma is a broad, heterogeneous group of lymphoid malignancies.
Transfusion Concepts
Packed red blood cells raise oxygen-carrying capacity in symptomatic anemia. Type and crossmatch reduces incompatibility risk. Acute hemolytic transfusion reaction (often ABO mismatch) is a medical emergency requiring immediate transfusion cessation and supportive care. Febrile nonhemolytic and allergic reactions are more common but generally less catastrophic. Know the difference between stopping the transfusion versus slowing it based on reaction severity.
Exam Strategy
Classify by MCV before ordering studies, localize bleeding with PT/aPTT/platelets, and match anticoagulants to their monitoring test and reversal agent.
A 47-year-old man has fatigue and a hemoglobin of 9.8 g/dL with a low MCV. Ferritin is low, serum iron is low, and total iron-binding capacity is high. What is the most appropriate next consideration?
Anemia of chronic disease; check inflammatory markers and observe
Iron deficiency anemia; replace iron and evaluate for a source such as occult GI blood loss
Vitamin B12 deficiency; start B12 replacement
Acute hemolysis; send a direct antiglobulin test
A patient on chronic warfarin therapy presents with minor bleeding and a markedly elevated INR. Which test is used to monitor warfarin, and which agent is most appropriate to address the elevated INR in this setting?
Monitored by aPTT; reverse with protamine
Monitored by INR; manage with vitamin K (and clotting factors if bleeding is serious)
Monitored by platelet count; reverse with a direct oral anticoagulant
Monitored by fibrinogen; reverse with enoxaparin
Which laboratory pattern is most consistent with disseminated intravascular coagulation (DIC)?
Normal PT, normal aPTT, normal platelets, normal fibrinogen
Prolonged PT and aPTT with low platelets and low fibrinogen
Isolated prolonged aPTT with normal platelets and normal PT
Isolated low platelets with normal PT, aPTT, and fibrinogen
Sections you finish are checked off in the contents.