Hemostasis Flashcards
How large are platelets, how long is their lifespan, and what organelle are they missing?
10 fL (about 1/10 size of an RBC), last 7-10 days, they lack nuclei but contain mRNA and all other organelles so they can make proteins
What hormone mediates the production of platelets and where is it produced?
Thrombopoietin, produced in liver and kidneys
What are the two types of granules in platelets and what do they release?
Delta = Dense = Dark -> release 4 things: ATP, ADP, serotonin, Ca+2
Alpha granules - light colored, release all the rest
What is the first step in primary hemostasis?
Reflex vasoconstriction -> from neural stimulation and endothelin release
Where is vWF made and what does it bind (binds two things)?
vWF - made in alpha granules and Weibel Palade bodies of endothelial cells
Binds Gp1b receptor on platelets when insoluble due to binding of subendothelial collagen
What is the most important function of the gpIIb/IIIa receptor? And can platelets directly bind collagen?
gpIIb/IIIa receptors attach platelets together by binding either side of fibrinogen
Platelets CAN directly bind collagen, via the gpIa or gp6 receptors.
What are the optimal levels of calcium and cAMP for platelet adhesion and activation? How does production of TXA2 help this?
Ca+2 - high, acts as a cofactor for many of the clotting factor conversions
cAMP - low
TXA2 blocks adenylate cyclase to keep cAMP levels low, while PGI2 increases adenylate cyclase activity
How does ADP improve hemostasis?
Binding of P2Y12 ADP receptor -> upregulates expression of GpIIb/IIIa receptors which improves platelet aggregation
What is the secondary function of vWF other than binding subendothelial collagen + platelets?
Also holds factor VIII and protects it from degradation (think of 8-ball in sketchy)
What is the first step of the coagulation cascade (secondary hemostasis), and which part of the pathway is most important?
Tissue factor (thromboplastin) binds factor VII when tissue damage occurs, which begins activity of the common pathway (10(5)-2-1)
-> amplification of intrinsic pathway by thrombin is most important and does majority hemostasis
How will a factor XIII deficiency show up in normal labs?
It won’t -> just functions to cross-like fibrin
- > thrombin activates 13a
- > it is past the common pathway, and will just lead to weaker clotting overall
How does thrombin and factor 13 actually work?
Thrombin -> cleaves two fibrinopeptides off of fibrinogen to make fibrin -> these will associated together but not be crosslinked
Factor 13 is activated by thrombin and induces the crosslinking of adjacent fibrin sticks
What is tPA / what makes it? How are fibrin split products generated?
tPA is made normal endothelium, (plasminogen activator inhibitor made if damaged). It converts plasminogen to plasmin. Plasmin cleaves cross-linked fibrin which produces “D-dimers” and “fragment E”
What type of bleeding occurs in disorders of primary hemostasis and why?
Primary hemostasis - blood vessel / platelet problem - bleeding from skin or mucous membranes (no initial plugs are formed), i.e. petechiae, ecchymoses and easy bruising
What type of bleeding occurs in disorders of secondary hemostasis and why?
Secondary hemostasis - cross-linking problem -> deeper bleeding problems with joints with lots of motion -> hemarthrosis, deep tissue bleeding, and rebleeding after surgical procedures
What is the most common cause of defective platelet function?
Aspirin and NSAID use
- > single dose causes defect for 7-10 days
- > inhibits TXA2 productionn
What is the definition of thrombocytopenia and thrombocytosis?
Thrombocytopenia: <150k/uL platelets
Thrombocytosis: >450k/uL platelets
How does platelet volume vary with platelet count?
Inversely
As platelet count increases, platelets get smaller
As platelet count gets lower, platelets get larger
What is the use in morphological evaluation of platelets on peripheral smear? When would you use EM?
Can look for granule problems, large platelets, or possible clumping which may have caused machine to misread the platelet count
Use EM to diagnose a granule storage pool deficiency
What is bleeding time used to assess and what is the normal range?
Normal range is 3-8 minutes, only used to assess disorders of platelets
Poor predictor of bleeding during surgery
What is the platelet aggregation assay / how does it work?
Take platelet-rich plasma, measure the optical density with spectrophotometer
- > add an agonist
- > as platelets begin to clot, the optical density of the solution falls (reduced turbidity)
- > release of ADP by activated platelets also contributes
What agonists are used to detect defects in GPIIb/IIIa and fibrinogen via the platelet aggregation assay? What disease may see a defect in this?
ADP, epinephrine, collagen, and thromboxane A2
Glanzmann thrombasthenia may be detected (GPIIb/IIIa deficiency) -> glassman saying 2 be or not 2b
What agonist is used to detect defects in GP1b and vWF via the platelet aggregation assay? What diseases might see defects in this?
Ristocetin -> activates vWF to bind GP1b in vitro
-> should catalyze clumping of platelets if there’s no defects in both
von Willebrand disease (defect in vWF with qualitative / quantitative changes)
Bernard-Soulier syndrome - genetic GPIb deficiency
What machine has now supplanted the bleeding test, and what drugs extend the coagulation time with Epinephrine and with ADP as an agonist?
Platelet function analyzer-100
Collagen + epi: Prolonged by aspirin
Collagen + ADP: prolonged by clopidogrel
What clotting factors are measured by the prothrombin time (PT) and what are frequent causes of prolonged PT?
Factors 1, 2, 7, 9, 10
Frequent:
- Vitamin K deficiency (fat malabsorption, premature infants, warfarin)
- Liver disease - decreased clotting factor production
- DIC - Fibrin / fibrinogen degradation products consumed
What are the two primary uses for aPTT?
- Monitoring of heparin and 2. factor replacement therapy in patients with hemophilia
(thrombin has a much larger effect on the intrinsic pathway)
What are some common causes of prolonged aPTT?
- Heparin - inhibits Xa and IIa
- Fibrin or fibrinogen degradation products / increased consumption - DIC
- Antiphospholipid / anticardiolipin antibodies - Lupus anticoagulant
- Liver disease
What is the value of a mixing study? How do you run one?
Can assess if a prolonged PT or aPTT is due to a clotting factor deficiency or presence of an inhibitor
Mix an equal amount of normal control plasma (with known PT / aPTT) and patient’s plasma, and measure the new PT / aPTT
What are the two possible results of the mixing study and what do they mean?
- Patient’s PTT / PT value is correct -> factor deficiency was the problem
- Patient PT/PTT value is not corrected -> an inhibitor like an antibody is binding clotting factors and rendering them useless. Also bind clotting factors in the control plasma
Give an example of a specific and a nonspecific inhibitor.
Specific - antibody against a clotting factor
Nonspecific - lupus anticoagulant - just binds anything
What is the TT and what does it measure? What are some causes of prolongation?
Thrombin Time
Thrombin-induced conversion of fibrinogen to fibrin, while bypassing all other factors
-> qualitative or quantitative defects in fibrin
-> thrombolytic therapy or heparin / thrombin inhibitor use
What vascular disease is also known as Osler-Weber-Rendu syndrome and what are its symptoms? Inheritance pattern?
Hereditary hemorrhagic telangiectasia - autosomal dominant
Dilated microvascular swellings (telangiectasias) which start in chidhood and increase in adulthood
- > recurrent bleeding of nose, skin, GI tract, and kidney
- > can lead to iron deficiency anemia and GI hemorrhage
What are the two most characteristic symptoms of Ehlers-Danlos syndrome and what causes it?
- Bleeding diathesis (Easy bruising, delayed wound healing)
- Joint hyperextensibility
Due to collagen defect
Give four acquired causes of easy bruising / spontaneous bleeding from small vessels (vascular disorders).
- Scurvy
- Senile purpura
- Purpura associated with infection
- Henoch-Scholein syndrome
What is senile purpura and what does it have in common with scurvy?
Purpura caused by atrophy of supporting tissue of cutaneous blood vessels
-> makes those purple spots you see on old people
Scurvy is different because it causes perifollicular petechiae, but tends to present in old people as well
What are some infectious causes of purpura?
Viral and bacterial infections
i.e. dengue fever, measles
Especially meningococcal septicemia (DIC caused by N. meningitidis)
What is Henoch-Schonlein syndrome and how is it acquired? Triad?
Most common childhood systemic vasculitis - follows acute URI
Triad: skin + GI + IgA nephropathy
Skin: palpable purpura on buttocks and lower legs
GI: abdominal pain
IgA nephropathy: hematuria and renal failure
Can also cause arthralgias
At what platelet count in thrombocytopenia will you actually get symptoms?
<50k / uL, whenever there is surgery or trauma
<20k / uL may cause spontaneous hemorrhage
How can the spleen be related to low platelet count?
In splenomegaly, up to 90% of platelets may be sequestered in the spleen
What are the two forms of Immune thrombocytopenic purpura (ITP) and who tends to get it?
Acute - in children weeks after a viral infection or immunization, usually self-limited
Chronic - seen more in adult women, often idiopathic but can be seen with other autoimmune disorders (i.e. SLE, HIV, HL)
What will labs and bone marrow biopsy show for ITP?
Labs - isolated thrombocytopenia
Bone marrow biopsy - megakaryocytic hyperplasia to compensate
What is the pathogenesis and treatment for ITP?
IgG antibodies are made to platelet receptors, and platelets are rapidly eaten by splenic macrophages
Treatment: Steroids, IVIG to distract macrophages, Rituximab to slow AB production, and splenectomy if refractory (removes site of removal)
What is TTP and what causes it?
Thrombotic Thrombocytopenic Purpura
Generally due to an autoantibody against but sometimes hereditary deficiency of ADAMTS13 -> metalloprotease which breaks down vWF multimers
Large vWF multimers induce platelet aggregation and thrombosis
What are the pentad of symptoms seen in TTP?
- Fever
- Thrombocytopenia
- Microangiopathic hemolytic anemia (with schistocytes)
- Renal symptoms (worse in HUS)
- NEUROLOGIC symptoms - i.e. involving CNS vessels
What is the treatment for TTP and what therapy is contraindicated?
Plasmapheresis using fresh frozen plasma with ADAMTS13
-> removes autoantibodies and ultralarge vWF multimers and replaces enzyme
Platelet transfusion contraindicated as it will cause more thrombosis
How tends to get hemolytic uremic syndrome and what are the clinical symptoms?
Especially children, those with exposure to E.coli O157:H7
Clinical symptoms:
Similar to TTP, except limited to renal insufficiency (involving vessels of kidney)
-> platelet replacement still contraindicated
What is Gabali’s mnemonic for TTP vs HUS?
Increased LDH (hemolysis) + adult+ thrombocytopenia + neurological symptoms = TTP
Increased LDH + kid + thrombocytopenia + renal symptoms = HUS
What causes post tranfusion purpura?
Either autoimmune reaction to donor platelet antigens, or simple dilution out of blood by adding only RBCs + saline -> drops the relative platelet count
What is Glanzmann thrombasthenia / inheritance pattern?
Autosomal recessive failure of platelet aggregation due to fibrinogen receptor deficiency (GpIIb/IIIa)
-> Think of glassman saying 2b or not 2b
How will platelets in Glanzmann thrombasthenia coagulate differently when given ADP/epi/collagen as agonist vs ristocetin?
ADP/epi/collagen - decreased platelet aggregation
Ristocetin - utilizes vWF receptors and Gp1b -> normal platelet aggregation
What disease is marked by an autosomal recessive deficiency in Gp1b receptors? What disease is it clinically similar to?
Bernard-Soulier syndrome
Similar to Von Willebrand disease
vONE is ONE Big Sucker (BS, 1b receptor)
What is the platelet count and appearance in Bernard Soulier syndrome?
Mild thrombocytopenia + platelets appear large
How will platelets in Bernard-Soulier syndrome coagulate differently when given ADP/epi/collagen as agonist vs ristocetin?
ADP/epi/collagen - normal platelet aggregation
Ristocetin - no response -> failure to aggregate (Gp1b receptor absent)
How do you tell von Willebrand Disease and Bernard Soulier apart?
Bernard-Soulier - bleeding tendency + thrombocytopenia + LARGE platelet size + no response to ristocetin
vWD - bleeding tendency + NO thrombocytopenia + NORMAL platelet size + no response to ristocetin
What anomaly is associated with thrombocytopenia in Alport syndrome?
May-Hegglan anomaly
-> Autosomal dominant mutation in myosin heavy chain gene
What is seen in peripheral smear in May-Hegglan anomaly?
Giant platelets, Dohle bodies in WBC, thrombocytopenia
What is absent in grey platelet syndrome and what can be seen in peripheral blood smear?
Alpha granules (light granules)
- > storage pool disorder
- > large platelets with no granules
How does kidneey dysfunction affect platelet function?
Uremia - associated with disrupted adhesion and aggregation
What is the most common clotting factor deficiency and what are the symptoms associated?
Factor 8 - Hemophilia A - X-linked
Joint and soft tissue bleeds, infants may have profuse hemorrhages.
Painful hemarthroses can lead to joint deformity
What are the lab findings of Hemophilia A, PT / aPTT, bleeding time
Prolonged aPTT Normal bleeding time (platelets not affected) Normal PT (factor 8 is cofactor for 9 in intrinsic pathway)
What is the treatment for hemophilia A and when do you need to be more aggressive?
Factor 8 replacement therapy + desmopressin (releases vWF from WP bodies which holds factor 8 / improves halflife)
be more aggressive when patient is having major surgery -> prevents bleeding (restore to 100% levels)
What is Christmas disease and what is the treatment? What is deficient?
Hemophilia B
- Factor 9 is deficient
- Treatment is recombinant factor 9
What is the most common inherited bleeding disorder and its inheritance pattern? What is the shared theme between the different types?
Von Willebrand disease
- autosomal dominant, except for a couple rare types
- > caused by defect or reduced production of vWF factor
Does von Willebrand disease look more like a platelet problem or clotting factor problem? What will happen to the bleeding time and thrombocyte count?
Although vWF carries Factor 8, prolongation of the aPTT is rare (but can be misdiagnosed as hemophilia of A in some types).
Looks like platelet problem -> mucosal and superficial bleeding
-> prolonged bleeding time from impaired platelet plug formation via the Gp1b receptor to vWF
Thrombocyte count is normal
What are the three broad types of von Willebrand disease?
Type 1 - All vWF multimer sizes present, but at low levels
Type 3 - All multimers absent
Type 2 - decrease in one particular multimer size
What are the primary treatments for vWD?
Type 1 - DDAVP - increase vWF release
Factor 8 concentrates which contain vWF
What is the definition of DIC and what are the laboratory findings? Include PT, PTT, and TT, fibrinogen / platelets, D-dimers, and peripheral smear.
Widespread microthrombi with consumption of coagulation factors and platelets due to procoagulant release or widespread endothelial damage
PT, PTT and TT all prolonged
Fibrinogen / platelets - decreased
D-dimers - elevated
Peripheral blood: microangiopathic hemolytic anemia leads to schistocytes
What are common causes of DIC?
Sepsis - endotoxins and cytokines induce endothelial cells to make tissue factor
Obstetric complications - thromboplastin in amniotic fluid
Malignancies - i.e. adenocarcinoma (mucin) and acute promyelocytic leukemia (Auer rods)
What is the treatment for DIC?
Treat the underlying cause, support care with cryoprecipitate with coagulation factors as necessary
What is the classic presentation for an acute hypercoagulable state? How should you test them in the acute phase and why?
Classic presentation is recurrent DVTs or DVTs at a young age
Test them with DNA-based tests since the acute-phase response and anticoagulant therapy can affect test results
-> use schematic testing for inherited thrombophilia based on most common disorders
What is the most common inherited hypercoagulability disorder in Caucasians and what causes it?
Factor V Leiden - single base pair polymorphism switches arginine to glutamine
- > factor V is resistant to cleavage by protein C
- > inheritance is co-dominant (worse when homozygous)
What is the second most common inherited hypercoagulability disorder in Caucasians and what causes it?
Prothrombin G->A Mutation
- > point mutation in 3’-UTR what causes overexpression of prothombin
- > increased prothrombin levels leads to hypercoagulability
What is the inheritance pattern of protein C / S deficiency and its claim to fame?
Autosomal dominant with variable penetrance
Causes skin necrosis due to dermal vessel thrombosis when treated with warfarin (both factors are vitamin K dependent)
What heritable hypercoagulability disorder is associated with decreased response to heparin? How can you acquire this disorder as well?
Antithrombin deficiency (no change in PT/aPTT, but heparin is ineffective since it holds antithrombin III)
Disorder is acquired in patients with renal failure / nephrotic syndrome -> loss of AT3 in urine
Increased levels of ______ in blood are associated with increased risk for both venous and ARTERIAL thrombosis.
Homocysteine
What are the causes of homocystinuria?
- Cystathione synthase deficiency or decreased affinity for B6 - requires B6 as a cofactor
- Methionine synthase deficiency
- Methylene tetrahydrofolate reductase deficiency -> requires B9 and B12 supplementation
How does estrogen increase thrombosis risk?
Estrogen therapy induces production of coagulation factors, increasing risk of thrombosis
It also tends to reduce the production of proteins C, S, and antithrombin III
->procoagulant state
What is the definition of antiphospholipid syndrome and what is it commonly seen in? What two antibodies are normally seen?
Arterial or venous thrombosis or recurrent miscarriage in association with evidence of persistent antiphospholipid antibodies
- > commonly seen as lupus anticoagulant syndrome (anticardiolipin antibodies)
- > Two antibody types: anticardiolipin and anti-Beta2 glycoprotein
What are the lab findings in antiphospholipid syndrome for PTT and mixing tests?
PTT - actually prolonged, since the antibodies bind the phospholipids needed for clotting in the lab (opposite occurs in vivo)
No correct with 50/50 mixes - antibodies react with donor plasma
-> can be corrected with excess phospholipid
How can children get antiphospholipid antibodies and are they associated with increased risk of bleeding?
Children get them post some viral infections (varicella, adenovirus) or juvenile autoimmune conditions (SLE, AIHA, JIA)
Prolonged PTT but NO increased risk of bleeding -> surgery OK
