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15 multiple-choice questions and 11 flashcards on Blood & Lymphoreticular / Immune Systems, about 9% of the USMLE Step 1 bank. Every one carries a written rationale.
Blood & Lymphoreticular / Immune Systems is one of 10 chapters in CoStudy's USMLE Step 1 — Medical Licensing bank, and it holds 15 of the bank's 172 multiple-choice questions — roughly 9% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
9 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
Type I hypersensitivity reactions are mediated by:
Answer: D — IgE-mediated mast cell degranulation — releasing histamine and other mediators (e.g., anaphylaxis, allergic asthma)
D) Defining mechanism. A/B/C) Each is a different hypersensitivity type.
A microcytic, hypochromic anemia with low ferritin and elevated total iron-binding capacity is most consistent with:
Answer: B — Iron-deficiency anemia
Iron-deficiency anemia: low ferritin (depleted stores), high TIBC (transferrin upregulated to grab any iron available). Anemia of chronic disease (A) typically has normal/high ferritin (sequestered) and low TIBC. Thalassemia (C) has normal iron studies. Sideroblastic (D) has elevated ferritin.
Warfarin inhibits which enzyme to produce its anticoagulant effect?
Answer: B — Vitamin K epoxide reductase
Warfarin blocks vitamin K epoxide reductase, preventing recycling of vitamin K to its active form. Without active vitamin K, hepatic γ-carboxylation of factors II, VII, IX, X (and proteins C and S) fails. (A) is heparin's mechanism. (D) is the mechanism of DOACs like apixaban.
A 30-year-old woman develops thrombocytopenia, microangiopathic hemolytic anemia, and altered mental status. Labs reveal markedly decreased ADAMTS13 activity. Which is the MOST appropriate initial treatment?
Answer: D — Plasma exchange (plasmapheresis)
D) Correct: TTP is caused by ADAMTS13 deficiency → uncleaved ultralarge vWF multimers → platelet aggregation. Plasma exchange replaces ADAMTS13 and removes the inhibiting autoantibody — life-saving. A) Platelet transfusion is CONTRAINDICATED in TTP (fuel for further thrombosis) — common Step 1 trap of doing what 'feels right' for low platelets. C) IVIG isn't first-line. B) Heparin is for DIC/HIT, not TTP. E) Splenectomy is for refractory ITP, not acute TTP.
Sickle cell anemia results from which mutation?
Answer: D — Glutamic acid→valine substitution at position 6 of the β-globin chain
HbS: single nucleotide change (GAG→GTG) → glutamic acid replaced by valine at β6. Under deoxygenation, HbS polymerizes, sickling RBCs.
A 28-year-old man presents with painless cervical lymphadenopathy and night sweats. Biopsy shows large binucleate cells with prominent owl-eye nucleoli within a mixed inflammatory background. Which lymphoma subtype has the BEST prognosis?
Answer: D — Lymphocyte-rich
D) Correct: of the classical Hodgkin lymphoma subtypes, lymphocyte-rich has the BEST prognosis (best survival, most reactive lymphocytes, fewest Reed-Sternberg cells). A) Lymphocyte-depleted has the WORST prognosis — direction reversal trap. B) Mixed cellularity has intermediate prognosis. C) Nodular sclerosis is the MOST COMMON subtype (young women, mediastinal mass) — common misconception that 'most common' = 'best prognosis'. E) NLPHL is a separate entity (not classical HL); it has indolent course but the question asks about classical HL subtypes.
A 45-year-old woman has fatigue and dyspnea. CBC: Hgb 9, MCV 110. Smear shows hypersegmented neutrophils. Serum methylmalonic acid is elevated. Which is the MOST likely cause?
Answer: B — Vitamin B12 deficiency from pernicious anemia
B) Correct: macrocytic anemia + hypersegmented neutrophils + elevated MMA = B12 deficiency. MMA distinguishes B12 from folate (folate raises homocysteine but NOT MMA). A) Folate deficiency causes the same megaloblastic picture but MMA is NORMAL — this is the key discriminator (common Step 1 question). C) Iron deficiency is microcytic (low MCV). D) Thalassemia is microcytic. E) ACD is normocytic or microcytic.
Which clotting factor deficiency is responsible for hemophilia A?
Answer: A — Factor VIII
Hemophilia A = Factor VIII deficiency (X-linked recessive). Hemophilia B = Factor IX deficiency (also X-linked). Both prolong PTT; PT normal.
A 65-year-old man presents with back pain and renal failure. Labs: hypercalcemia, anemia, and elevated total protein with a monoclonal IgG spike on SPEP. X-ray shows lytic lesions in the skull. Which finding on bone marrow biopsy would CONFIRM the diagnosis?
Answer: A — >10% plasma cells
A) Correct: multiple myeloma is diagnosed with monoclonal protein, end-organ damage (CRAB: hyperCalcemia, Renal failure, Anemia, Bone lesions), and ≥10% clonal plasma cells in marrow. B) >20% blasts defines acute leukemia — wrong neoplasm. C) Reed-Sternberg cells = Hodgkin lymphoma (no lytic bone lesions or M-spike). D) Hypercellular marrow with megakaryocytes = essential thrombocythemia or other MPN. E) Hairy cells = hairy cell leukemia (B-cell, no lytic lesions).
4 cards from the 11 in this chapter.
Hypersensitivity types?
Type I (immediate, IgE), II (cytotoxic, IgG/IgM), III (immune complex), IV (delayed, T cells).
Macrocytic anemia DDx?
B12 deficiency, folate deficiency, drugs (methotrexate), liver disease, hypothyroidism.
Microcytic anemia DDx?
Iron deficiency, thalassemia, anemia of chronic disease, sideroblastic.
Sickle cell anemia mutation?
Glu → Val at position 6 of β-globin. Autosomal recessive.
These are a sample. The full Blood & Lymphoreticular / Immune Systems chapter runs 26 items with per-chapter progress tracking, on the web and in the iOS app.
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