Hematology Board Prep for Family Medicine

Five-minute daily sessions on anemia workups, anticoagulation decisions, and the blood disorders family physicians manage every week.

Hematology is one of the smaller ABFM content areas by percentage, but it punches above its weight for two reasons: anemia is one of the most common laboratory abnormalities in primary care, and anticoagulation management generates real decisions — with real consequences — in nearly every family medicine panel. The exam concentrates on exactly those two pillars, plus venous thromboembolism diagnosis and a handful of recognition-level questions about bleeding disorders and hematologic malignancy red flags.

Anemia questions are workup questions. The exam gives you a CBC and expects a disciplined path: classify by MCV, use the reticulocyte count to separate underproduction from loss or destruction, and interpret iron studies without shortcuts. The single most tested downstream decision is what iron deficiency means in the wrong patient — a man or postmenopausal woman with unexplained iron deficiency anemia needs bidirectional endoscopy, because occult GI malignancy is the diagnosis you cannot miss.

Anticoagulation questions have consolidated around DOACs. Apixaban and rivaroxaban dominate stems about atrial fibrillation and VTE treatment, with warfarin persisting where it is genuinely required: mechanical valves, moderate-to-severe mitral stenosis, and antiphospholipid syndrome. Know the reversal agents, the periprocedural interruption rules, and the warfarin INR playbook — including the counterintuitive, well-tested fact that an INR between 4.5 and 10 without bleeding calls for holding warfarin, not vitamin K.

The rest of the category is pattern recognition with clear referral lines: the thrombocytopenic patient who needs urgent evaluation versus watchful waiting, the MGUS finding that needs monitoring versus myeloma workup, thalassemia trait versus iron deficiency on a CBC, and sickle cell disease health maintenance. Family medicine hematology is about finding the dangerous needle in a very common haystack — which is precisely what the exam simulates.

High-yield hematology topics

• Anemia classification by MCV and reticulocyte count. Microcytic: iron deficiency, thalassemia, anemia of chronic disease (can be normocytic), sideroblastic. Macrocytic: B12 and folate deficiency, alcohol, hypothyroidism, medications, myelodysplasia in older adults. A low reticulocyte index means underproduction; a high one means bleeding or hemolysis — then check LDH, haptoglobin, bilirubin, and the smear.
• Iron deficiency: diagnosis, cause, and treatment. Ferritin is the best single test — low ferritin is diagnostic, but ferritin is an acute-phase reactant, so values up to 100 can still hide deficiency in inflammation. Unexplained iron deficiency in men and postmenopausal women mandates GI evaluation. Iron is absorbed in the duodenum and proximal jejunum — duodenal disease like celiac impairs it. Alternate-day oral dosing improves absorption and tolerance; IV iron for intolerance, malabsorption, or CKD.
• B12 deficiency and its neurology. Suspect with macrocytosis, glossitis, paresthesias, or subacute combined degeneration (posterior column signs); neurologic disease can precede anemia. Confirm borderline levels with methylmalonic acid. Causes: pernicious anemia, metformin, PPIs, gastric surgery, vegan diet. High-dose oral B12 is as effective as injections for most patients. Treating folate deficiency without checking B12 can let neurologic damage progress.
• DOAC selection, dosing pitfalls, and reversal. Apixaban and rivaroxaban lead for AF and VTE; dabigatran has idarucizumab for reversal, factor Xa inhibitors have andexanet alfa. Avoid DOACs in mechanical valves, moderate-to-severe mitral stenosis, antiphospholipid syndrome, and pregnancy. Know apixaban dose-reduction criteria for AF (two of three: age 80 or older, weight 60 kg or under, creatinine 1.5 or higher) — underdosing without criteria is a tested error.
• Warfarin management and the elevated INR. INR 4.5 to 10 without bleeding: hold warfarin and recheck — no routine vitamin K. INR above 10 without bleeding: hold and give oral vitamin K. Major bleeding at any INR: four-factor prothrombin complex concentrate plus IV vitamin K. Interactions to know: TMP-SMX, metronidazole, fluconazole, and amiodarone raise INR; rifampin and carbamazepine lower it.
• VTE diagnosis and treatment duration. Use Wells scores with d-dimer: low pretest probability plus negative d-dimer excludes DVT and PE without imaging; age-adjusted d-dimer cutoffs improve specificity over 50. Treat provoked VTE for three months. Unprovoked VTE warrants discussion of extended therapy after three months based on bleeding risk. Do not order thrombophilia testing during the acute event or while anticoagulated.
• Thrombocytopenia triage: ITP, drug-induced, and TTP. Isolated low platelets in a well adult with a normal smear suggests ITP — observe if above 30,000 without bleeding; treat with steroids or IVIG when lower or bleeding. Always review medications (heparin, sulfa drugs, quinine). Fever, neurologic changes, hemolysis with schistocytes, and thrombocytopenia suggest TTP — an emergency requiring plasma exchange, not platelet transfusion.
• Recognition-level heme: thalassemia, MGUS, sickle cell maintenance. Thalassemia trait: microcytosis out of proportion to anemia, normal-to-high RBC count, normal ferritin, Mentzer index under 13 — confirm with hemoglobin electrophoresis and do not give iron. MGUS: M-protein under 3 g/dL, no CRAB features — monitor; refer when criteria are exceeded. Sickle cell disease: hydroxyurea, vaccination against encapsulated organisms, and annual screening exams are the tested maintenance items.

ABFM exam tips

Ferritin decides iron deficiency — and low ferritin decides more than that. In a man or postmenopausal woman, unexplained iron deficiency is a GI workup, full stop. The question is rarely "is this iron deficiency" and usually "what does this iron deficiency require next" — the answer is endoscopy, not just iron tablets.

Hold, don't reverse, the asymptomatic high INR. Between 4.5 and 10 without bleeding, the evidence-based move is holding warfarin alone. Vitamin K enters at INR above 10, and IV vitamin K plus four-factor PCC is reserved for major bleeding. This exact gradient is one of the most reliably tested facts in the category.

Match the smear finding to the emergency. Schistocytes plus thrombocytopenia is a microangiopathy — think TTP and start plasma exchange arrangements. Blasts mean acute leukemia. Teardrops and nucleated RBCs suggest marrow infiltration. The smear description in a stem is never decorative.

Use the Mentzer index before prescribing iron for microcytosis. MCV divided by RBC count: under 13 suggests thalassemia trait, over 13 suggests iron deficiency. Iron given for thalassemia trait is a wrong answer with a real-world harm — iron loading.

Check B12 before treating with folate. Folate corrects the anemia while B12-related neurologic injury progresses. Any macrocytic anemia stem with paresthesias or gait complaints is steering you toward B12, methylmalonic acid confirmation, and prompt repletion.

Low-risk Wells plus negative d-dimer means stop. No ultrasound, no CT angiogram. The exam tests diagnostic restraint as heavily as diagnostic action, and unnecessary imaging in low-probability VTE is a favorite way to do it.

Common pitfalls

Do not transfuse platelets in TTP. Platelet transfusion can fuel the microvascular thrombosis. The treatment is urgent plasma exchange with steroids. Confusing TTP with ITP — or treating either with platelets outside life-threatening bleeding — is a classic error the exam invites.

Do not order thrombophilia panels during acute VTE. Acute thrombosis and anticoagulants both distort the results, and the findings rarely change initial management. Testing, when indicated at all, happens after treatment completion and off anticoagulation. Reflexive panels are a tested wrong answer.

Do not miss the inflammation exception for ferritin. A ferritin of 60 in a patient with rheumatoid arthritis or CKD does not exclude iron deficiency. Use transferrin saturation and the clinical context; in CKD, thresholds for treating are higher and IV iron is often preferred.

Do not put a DOAC on a mechanical valve. Dabigatran was tested and harmful (RE-ALIGN); the class is contraindicated. Mechanical valves, moderate-to-severe mitral stenosis, antiphospholipid syndrome, and pregnancy remain warfarin (or heparin) territory. This list is short and heavily tested.

Do not treat anemia of chronic disease with iron by reflex. Low iron plus low TIBC plus normal-or-high ferritin is sequestration, not deficiency — treat the underlying disease. Iron helps only when true deficiency coexists. The iron-studies pattern recognition is the whole question.

Do not dismiss mild persistent lymphocytosis or an M-protein without follow-up. CLL and MGUS are common incidental findings in older adults; each has defined monitoring, and each has red-flag thresholds (lymphocyte doubling, CRAB features) that convert monitoring into referral. Both extremes — ignoring and over-referring — appear as distractors.

Do not bridge every warfarin interruption. Bridging with heparin is reserved for the highest thrombotic risk (mechanical mitral valve, recent stroke or VTE, severe thrombophilia). Routine bridging for atrial fibrillation increases bleeding without benefit (BRIDGE trial) and is a tested outdated practice.

Frequently asked questions

What hematology topics are most tested on the ABFM?

Anemia workup dominates: iron deficiency diagnosis and its mandatory GI evaluation in the right demographics, B12 deficiency with neurologic features, and the microcytic differential including thalassemia trait. Anticoagulation is the second pillar: DOAC selection and contraindications, warfarin INR management, periprocedural decisions, and VTE diagnosis with Wells and d-dimer.

How much hematology is on the ABFM exam?

The hematologic and immunologic content area is one of the smaller blueprint slices — a low single-digit percentage. But anticoagulation decisions also surface inside cardiology and perioperative questions, and anemia appears in geriatric, GI, and women's health stems, so the working footprint is meaningfully larger than the blueprint number suggests.

Which anticoagulant should I choose on exam questions?

Default to apixaban or another DOAC for nonvalvular atrial fibrillation and routine VTE. Switch to warfarin for mechanical valves, moderate-to-severe mitral stenosis, and antiphospholipid syndrome; use low-molecular-weight heparin or specific regimens in pregnancy and some cancer scenarios. If the stem includes severe renal impairment, apixaban is the DOAC with the most supportive dosing pathway.

What do I need to know about elevated INR management?

The three-tier rule: INR 4.5 to 10 without bleeding — hold warfarin, no routine vitamin K; INR above 10 without bleeding — hold and give oral vitamin K; any major bleeding — four-factor prothrombin complex concentrate plus IV vitamin K. Also know the common interacting drugs, because many stems start with a new antibiotic.

When does iron deficiency anemia require endoscopy?

In any man, any postmenopausal woman, and any patient with GI symptoms or a positive fecal occult blood test — unexplained iron deficiency in these groups requires bidirectional endoscopy to exclude GI malignancy. In young menstruating women with a clear source, a trial of iron without endoscopy is appropriate. Celiac serology belongs in the workup when the pattern fits malabsorption.

How do I tell thalassemia trait from iron deficiency quickly?

Thalassemia trait shows marked microcytosis with only mild anemia, a normal or elevated RBC count, normal ferritin, and a Mentzer index (MCV/RBC) under 13. Iron deficiency shows a low RBC count, low ferritin, high RDW, and a Mentzer index over 13. Confirm thalassemia with hemoglobin electrophoresis — and remember alpha trait can have a normal electrophoresis.

How should I study hematology in five-minute daily sessions?

Drill the interpretive patterns — iron studies, the INR tiers, Wells-plus-d-dimer logic, and smear findings — because hematology questions are pattern-in, decision-out. Spaced repetition suits these tightly structured facts, and a few applied vignettes per week keep the "what comes next" reflexes (endoscopy, plasma exchange, hold the warfarin) sharp.