PowerPoint Presentation - Week 6: Secondary Hemostasis
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Week 6: Secondary Hemostasis
Plasmatic factors
Intrinsic pathway
Extrinsic pathway
Specimen
PPP preparation
PT, INR
APTT
TT
Vitamin K
Liver disease
Factor deficiency
Circulating inhibitors
Heparin
Coumarin
Lupus inhibitor
Factor assay
Mixing and substitution
studies
5M urea test
Lee-White clotting time
Plasmatic Factors
Intrinsic pathway activated by contact to
collagen: HMWK, prekallikrein, XII, XI,
IX, VIII
Extrinsic pathway activated by tissue
thromboplastin: VII
Common pathway: X, V, II, I
RBC’s trapped in fibrin strands SEM x 6,400
Fibrin Formation
D and E domains on fibrinogen
Thrombin cleaves fibrinopeptides
Spontaneous polymerization (unstable)
Disulfide cross-linkages between D
domains by the action of XIII
Inhibitors
Anti-thrombin III with heparin: II, IX, X,
XI, XII
Protein C and protein S: slow down VIII
and V
Heparin: quick acting but short lived and
need AT-III
Coumarin: vitamin K antagonist
Vitamin K Dependent Factors
Caboxylation to chelate Ca++
II, VII, IX, X, protein C, protein S
Liver synthesis inhibited by coumarin
Specimen
Clean phlebotomy required
3.2% vs 3.8% citrate
1:9 citrate to blood ratio
Transport to lab quickly and separate
plasma
Platelet poor plasma (PPP)
Test without delay or store frozen
Instrumentation
Electro-mechanical (e.g., Fibrometer)
Physical detection of clot
Cannot be automated
Optical (e.g., MLA, ACL)
Interference with icteria or lipemia
Can be automated
Basic Hemostasis Tests
Plasmatic factors
Thrombin time
Prothrombin time
Activated Partial
Thromoplastin time
5M urea test (factor
XIII)
Platelet
Platelet count
Platelet function test
Vascular integrity
Bleeding time
Tourniquet test
Others
FDP, D-dimer
Factor assays
Anti-thrombin III
Proteins C and S
Factor V Leiden
Activated Partial Thromboplastin
Time (APTT)
For intrinsic pathway factors
Lee-White clotting time
o
Whole blood at 37 C
Glass test tube for surface
Phospholipid platelet substitute
Activator: kaolin
0.02M CaCl2
Monitor heparin therapy
Prothrombin Time (PT)
For extrinsic pathway factors
Tissue thromboplastin (rabbit brain) with
Ca++
European labs use Tpl from human source,
so more sensitive
INR = (Pt PT/normal PT)ISI
Monitor coumarin therapy
Thrombin Time (TT)
Fibrinogen screen
Thrombin reagent
Clotting time corresponds to fibrinogen
level
Other Tests
Factor assay: reconstitute patient plasma
with known deficient plasma and determine
clotting time
FDP and D-dimer tests for fibrinolysis
Fibrinogen assay: modified TT
5M urea test for factor XIII
Plasma protamine-sulfate paracoagulation
test (3P) for fibrin monomers
Mixing and Substitution Tests
1:1 with normal plasma: screen for
circulating inhibitor
Aged serum has: II, VII, IX, XI, XII
Barium sulfate adsorbed plasma has: I, V,
VIII, XI, XII
Abnormal Coagulation Tests
Check specimen collection
Phlebotomy, anticoagulant
Patient condition
Medication
Check specimen integrity
Storage temperature
PPP preparation
Check reagent integrity
Check instrument QC
Abnormal APTT
Hemophilia A (VIII) if male
Christmas disease (IX) if male
Liver disease: multi-factor deficiency
Hypofibrinogenemia
Heparin
Anti-phospholipid antibody (Lupus inhibitor): do
a 1:1 mix with normal plasma
Von Willebrand’s: variable
Abnormal PT
Coumarin therapy
Vitamin K deficiency, especially in newborn
More sensitive to common pathway factors
than APTT
Heparin
Abnormal TT
Dysfibrinogenemia
Afibrinogenemia
Hypofibrinogenemia
Heparin
FDP: forms abnormal complex
Hyper-coagulable State
Deep vein thrombosis due to inappropriate
coagulation
Protein C and protein S deficiency
Anti-thrombin III deficiency
Factor V Leiden mutation: does not
respond to protein C (activated protein C
resistance, APCR)