Basic Science: Hematology

What is the migration order of plasma proteins on SPEP from fastest to slowest?

Albumin → alpha-1 → alpha-2 → beta → gamma

What determines migration speed on protein electrophoresis — size or charge?

Net electrical charge (not size/weight)

Why does albumin migrate fastest on SPEP?

It has a strong negative charge, pulling it hardest toward the anode

Why do gamma globulins migrate slowest on SPEP?

They're a heterogeneous population with weak/variable net charge

What special stain reveals the reticular mesh pattern in reticulocytes?

Supravital stain (e.g., new methylene blue) — NOT routine Wright-Giemsa

Why do reticulocytes show a mesh/reticular pattern on supravital stain?

Residual ribosomal RNA precipitates into that pattern

How long do reticulocytes circulate before full maturation, and what is total RBC lifespan?

~1 day circulating (included in, not added to) a total ~120 day RBC lifespan

Why is reticulocyte count preferred over RBC count to assess current marrow activity?

Retic count reflects real-time output (last ~24h); RBC count is an accumulated total that lags behind

What does a high reticulocyte count with anemia indicate?

Marrow is healthy and compensating for peripheral RBC destruction/loss

What does a low/normal reticulocyte count with anemia indicate?

A bone marrow production problem

What cell types arise from a myeloid stem cell?

RBCs, platelets, granulocytes (neutrophil/eosinophil/basophil), monocytes

What cell types arise from a lymphoid stem cell?

T cells, B cells, NK cells

What organ produces erythropoietin, and what triggers its release?

Kidney; triggered by tissue hypoxia

What are the kidney's three main hormone/hormone-like products?

Renin, erythropoietin (EPO), calcitriol (activated vitamin D)

What factors cause a right shift of the Hgb-O2 dissociation curve?

↑Temp, ↑PCO2, ↑2,3-DPG, ↓pH (acidosis)

What factors cause a left shift of the Hgb-O2 dissociation curve?

↓Temp, ↓PCO2, ↓2,3-DPG, ↑pH (alkalosis)

What is the mnemonic for factors causing a right shift?

CADET, face Right! (CO2, Acid, DPG, Exercise, Temp ↑)

Does a right shift promote O2 loading or unloading, and where does this occur?

Unloading; occurs at the tissues

Does a left shift promote O2 loading or unloading, and where does this occur?

Loading; occurs at the lungs

Mechanistically, how does ↑CO2 cause a right shift?

↑CO2 → ↑H+ → H+ binds Hgb allosterically → shape change → ↓O2 affinity

Why does lower temperature increase Hgb's O2 affinity (left shift)?

Less molecular motion stabilizes the Hgb-O2 bond, so it's less likely to release O2

What percentage of O2 is carried on hemoglobin vs. dissolved in plasma?

~98% on hemoglobin, ~2% dissolved

Why do aged RBCs eventually rupture in capillaries?

No protein synthesis (no nucleus/ER) + limited energy (no mitochondria) → membrane stiffens, loses plasticity, can't deform to squeeze through capillaries

What happens to bilirubin after RBC hemolysis?

Releases unconjugated bilirubin → liver conjugates it → excreted in bile

In anemia classification, what lab value best discriminates ↑destruction from ↓production?

Reticulocyte count

What is the MCV, retic count, and cause pattern for iron deficiency anemia?

↓MCV (microcytic), ↓/normal retic; chronic blood loss or poor intake

What is the MCV, retic count, and cause pattern for aplastic anemia?

Normal MCV, ↓↓retic; CKD (↓EPO) or marrow failure

What is the MCV, retic count, and cause pattern for megaloblastic anemia?

↑MCV (macrocytic), ↓/normal retic; B12/folate deficiency, impaired DNA synthesis

What is the MCV, retic count, and cause pattern for hemolytic anemia?

Normal MCV, ↑↑retic; G6PD deficiency, sickle/thal, infection, autoimmune, mechanical

Why is MCV normal in aplastic anemia despite significant anemia?

It's a quantity problem (not enough cells made), not a quality/size problem — cells made are normal size

Why does megaloblastic anemia produce macrocytic (oversized) RBCs?

Impaired DNA synthesis slows nuclear division while cytoplasm keeps growing; many die in marrow (ineffective erythropoiesis)

Why is MCV normal in hemolytic anemia?

The marrow builds normal RBCs; they're just destroyed prematurely elsewhere — production process itself isn't broken

What is G6PD deficiency and why does it cause hemolysis?

Enzyme deficiency impairing NADPH production, leaving RBCs unable to handle oxidative stress → hemolysis with triggers (infection, sulfa drugs, fava beans)

What causes primary polycythemia (polycythemia vera)?

Intrinsic marrow overactivity, often JAK2 mutation; EPO often LOW

What causes appropriate secondary polycythemia?

Chronic hypoxia (COPD, high altitude) driving a genuine EPO-mediated compensatory increase

What law explains why polycythemia causes sluggish blood flow/hypoxia?

Poiseuille's law (viscosity inversely related to flow) — NOT Fick's law

What is the function of neutrophils, and what are their two killing mechanisms?

First responders vs. bacteria; O2-dependent (respiratory burst) and O2-independent (enzymes like lysozyme) killing

What is the function of eosinophils?

Modulate allergic reactions, kill parasites

What is the function of basophils?

Mast cell precursor-related, contain large basophilic granules

What is the function of monocytes?

Precursor to macrophages (Kupffer cells, alveolar macrophages, histiocytes)

What are the 3 compartments of lymphocyte development?

1) Bone marrow (progenitor) 2) Primary lymphoid tissue (thymus=T, marrow=B; lineage commitment) 3) Secondary/peripheral lymphoid tissue (nodes, spleen, MALT; antigen encounter/maturation)

What causes leukopenia?

↓WBC production from marrow injury/inhibition (viral infection, immunosuppressants, radiation) → ↑infection risk

What is leukemia?

Neoplastic proliferation of leukocytes; myelocytic or lymphocytic, acute or chronic

What defines thrombocytopenia?

LOW platelet count (↓production or ↑destruction/consumption)

What defines thrombasthenia?

NORMAL platelet count but defective platelet FUNCTION (inherited or drug-induced)

What drug class intentionally induces a thrombasthenia-like state?

Antiplatelet drugs (aspirin, clopidogrel)

What defines thrombocytosis and its two categories?

Excess platelets; reactive/secondary (infection, inflammation, post-splenectomy) or primary (essential thrombocythemia)

What does hematocrit measure, and what raises/lowers it?

% blood volume that is RBC; ↑ in dehydration/polycythemia, ↓ in anemia/hemodilution

How is MCV calculated and what does it classify?

Hct/RBC count; classifies anemia by size (micro/normo/macrocytic), NOT severity

How is MCH calculated?

Hgb/RBC count

What does MCHC classify?

Normochromic vs. hypochromic anemia

What are the 4 steps of hemostasis in order?

1) Vasoconstriction 2) Platelet plug formation 3) Fibrin clot formation 4) Vessel repair

What role does vWF play in hemostasis?

Mediates platelet adhesion to exposed collagen during platelet plug formation

What causes a formed clot to contract and express serum?

Contractile proteins (actin/myosin) in platelets pulling the clot inward, like muscle contraction

What triggers the intrinsic coagulation pathway?

Contact activation — exposed negatively-charged subendothelial collagen (factor XII)

What triggers the extrinsic coagulation pathway?

Tissue factor (factor III) release from penetrating injury

What is the intrinsic pathway factor sequence?

XII → XI → IX → VIII → converges at X

What is the extrinsic pathway factor sequence?

III → VII/VIIa → converges at X

What is the common pathway sequence?

Xa → prothrombin (II) → thrombin → fibrinogen (I) → fibrin

What lab test evaluates the intrinsic + common pathway?

APTT

What lab test evaluates the extrinsic + common pathway?

PT/INR

Do the intrinsic and extrinsic pathways typically activate separately or together in real injury?

Together — both usually activate simultaneously in real vessel injury

At which steps is calcium required in the coagulation cascade?

Multiple steps — generation of factor Xa AND conversion of prothrombin to thrombin

What is the bus/motorcycle analogy for intrinsic vs. extrinsic pathways?

Intrinsic = slow bus (scenic route, more stops/factors); Extrinsic = fast motorcycle (shortcut)

What does factor XIIIa do?

Cross-links fibrin strands, stabilizing the clot

What specifically produces a D-dimer fragment?

Breakdown of cross-linked (factor XIIIa-stabilized) fibrin specifically

Why is D-dimer more specific than other FDP fragments (X, Y, D, E)?

It only comes from breakdown of a truly stabilized (cross-linked) clot

What does a low/negative D-dimer suggest clinically?

Reassuring — no significant clot present to be broken down (helps rule OUT DVT/PE)

What does a high D-dimer suggest, and what's its limitation?

Suggests clot formation/breakdown occurred somewhere; nonspecific (elevated in pregnancy, surgery, infection, cancer, age)

What is the "ash from a fire" analogy for D-dimer?

Breakdown itself isn't the danger; a LARGE amount signals a bigger-than-normal clot existed, just like lots of ash signals a bigger fire

What does antithrombin III (AT-III) inhibit?

Thrombin (IIa) and factor Xa

How does heparin work?

Acts as a cofactor that massively amplifies AT-III's activity (doesn't work independently)

What does Protein C inactivate, and what is its cofactor?

Inactivates factors VIIIa and Va; requires Protein S as cofactor

Are AT-III/heparin and Protein C/S triggered by injury, or continuously active?

Continuously active in parallel — "daily security patrol" vs. the cascade's "SWAT team" response

What is fibrinolysis and what enzyme carries it out?

Breakdown of fibrin clot; plasminogen → plasmin (via tPA/urokinase)

What fragments does fibrin breakdown produce?

FDPs: fragments X, Y, D, E, and D-dimer

What does bleeding time test, and what's the normal range?

Platelet function (primary hemostasis); ~2-5 minutes

What factors are vitamin K-dependent?

II, VII, IX, X (plus Proteins C and S)

What is the mnemonic for vitamin K-dependent factors?

"1972" — factors 10, 9, 7, 2

What deficiency causes Von Willebrand Disease, and what TWO defects does it cause?

vWF deficiency; causes BOTH platelet dysfunction (↑bleeding time) AND intrinsic pathway deficit (↑APTT, since vWF stabilizes factor VIII)

What factor is deficient in Hemophilia A vs. Hemophilia B?

A = factor VIII; B = factor IX

Why do Hemophilia A and B present almost identically?

Both only affect the intrinsic pathway (↑APTT, normal bleeding time) — factor level testing needed to distinguish

What distinguishes innate from acquired immunity?

Innate = fast, non-specific, no memory (barriers, neutrophils, macrophages, NK cells, complement); Acquired = specific, has memory (T/B cells, antibodies)

What are the three complement activation pathways and their triggers?

Classical (antibody-antigen complex), Alternative (spontaneous on pathogen surface, no antibody), Lectin (binds pathogen sugars)

What are the functions of the complement cascade?

Opsonization, cell lysis (MAC), chemotaxis, inflammation

How does cellular immunity handle intracellular pathogens like viruses?

Cytotoxic T cells directly kill infected/tumor cells

How does humoral immunity handle extracellular pathogens like bacteria/toxins?

B cells differentiate into plasma cells → secrete antibodies → neutralize, opsonize, activate complement

What is opsonization, and what two things can act as opsonins?

Coating a pathogen to tag it for phagocytosis; antibodies (IgG) OR complement (C3b)

Which antibody class crosses the placenta?

IgG

Which antibody class is made first in a primary response, and what is its structure?

IgM; pentamer

Which antibody class dominates at mucosal surfaces/secretions?

IgA

Which antibody class is involved in allergy/parasite defense, binding mast cells/basophils?

IgE

What is the mechanism of Type I hypersensitivity, and give an example

IgE-mediated mast cell degranulation; anaphylaxis, asthma, food allergy

What is the mechanism of Type II hypersensitivity, and give an example

IgG/IgM against cell-surface antigens → complement/phagocytosis; transfusion reaction

What is the mechanism of Type III hypersensitivity, and give an example

Antigen-antibody immune complexes deposit in tissue; serum sickness, lupus, post-strep GN

What is the mechanism of Type IV hypersensitivity, and give an example

T-cell mediated, NO antibody, delayed 24-72h; TB skin test, contact dermatitis, acute transplant rejection

What is the mnemonic for the 4 hypersensitivity types?

ACID — Allergic(I), Cytotoxic(II), Immune complex(III), Delayed(IV)

What hypersensitivity type is PANDAS/rheumatic fever, and why?

Type II — molecular mimicry, antibody directly targets a self-antigen resembling strep antigen

What hypersensitivity type is lupus predominantly, and why?

Type III — immune complex deposition (though some Type II features occur too, e.g. autoimmune hemolytic anemia)

Which hypersensitivity type is transplant hyperacute rejection?

Type II (pre-existing antibodies)