lecture 3, spring 2014
TRANSCRIPT
Lecture 3
Coagula.on Assays
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XII
XIIa
XI XIa
IX
X X
VII
IIa II
Fibrin Fibrinogen
VIIa TF
TF
IXa VIIIa
Xa Va
Intrinsic
Common
Extrinsic
Cell-‐based Model of Hemostasis
• Proposed to replace the tradi.onal cascade – more accurately explains coagula.on in vivo
• Specific cellular surface receptors for coagula.on proteins promote hemostasis
• Platelets and Thrombin are central
• Occurs in 3 phases ▫ 1. Ini.a.on ▫ 2. Amplifica.on ▫ Propaga.on
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XII
XIIa
XI XIa
IX
X X
VII
IIa II
Fibrin Fibrinogen
VIIa TF
TF
IXa VIIIa
Xa Va
Xa Va
XIa
IIa
Fibrin Fibrinogen
VIIa TF
IXa VIIIa
Xa
IIa
Fibrin Fibrinogen
XIa
VIIa TF
IXa VIIIa
Plt
Xa IIa VIIa TF
Xa Va
IIa Plt
Xa
IXa VIIIa
Xa Va
IIa
Plt
Plt
Fg
Fb
vWF
Fb
Plt
Plt Fb
Fb
Fb
vWF
Tissue factor bearing cell
Subendothelial collagen
Plt
IIa
Ini.a.on
Amplifica.on
Propaga.on
Platelet Ac.va.on
• Results in ▫ Greatly increased surface area ▫ Dense granules release Ca2+,TXA2, ADP, Serotonin ▫ Alpha granules release FV, fibrin, vWF
• Platelet phospholipid bilayer is ac.vely controlled • Res.ng internal surface is procoagulant • Bilayer flips outward during ac.va.on, exposing procoagulant surface
Plt
Xa IIa VIIa TF
Xa Va
Plt
XIa
IIa
IXa
VIIIa
Va
Fg vWF
IIa Plt
Xa
IXa VIIIa
Xa Va
Plt
Plt
Plt IIa
TXA2
5HT
Plt
Plt
Fg
Fb
vWF
Fb
Plt
Plt Fb
Fb
Fb
vWF
Tissue factor bearing cell
Subendothelial collagen
IIa
IIa
IIa
Plt
IIa
IXa VIIIa
ADP
Propaga.on
• PT/INR • aPTT • Fibrinogen • Thrombin • Rep.lase Time • D-‐Dimer • FSP
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Prothrombin Time (PT) • Armand Quick 1935 • Measures the .me required for fibrin clot to
form when plasma is added to [TF + Ca2+] mixture
• TF combines with FVII to form the “extrinsic” tenase complex
• Measures a. FVII of the extrinsic pathway b. FX, FV, FII, FI of the common pathway c. Measures 3 of the vitamin K-‐dependent
factors • II, VII, X – does not measure IX
• PT is prolonged in – Deficiencies of I, II, V, VII, X – Liver Disease, – Warfarin (Coumadin) – OAT – High dose heparin therapy and DTI’s
• PT is shortened following treatment with rVIIa • Most common use of PT à monitoring OAT
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Pa.ent Plasma
Ca2+ +
Thromboplas.n (TF)
Monitoring OAT
• Problems with the PT ▫ Commercially available thromboplas.ns
vary in their sensi.vity to VKDF’s ▫ PT values that result from using different
thromboplas.ns are not interchangeable
• INR developed by WHO using an IRP to which all other thromboplas.ns can be compared ▫ Recommended that a PT value be expressed
as a ra.o by normalizing it to the IRP
▫ ISI = measure of the sensi.vity and responsiveness of a par.cular thromboplas.n reagent to warfarin-‐induced reduc;on of the VKDF’s
▫ ISI of the IRP = 1.0 Advantages: INR for monitoring pa.ents on OAT 1. Minimizes the varia.on in the PT assay 2. Allows comparability of PT results among
different laboratories
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Pa.ent’s PT GM Normal PT
INR = (ISI)
Reagent PT (sec)
A 18
B 20
C 22
D 18
E 31
ISI INR
3.2 2.6
2.4 2.6
3.0 2.6
1.2 2.6
1.0 2.6
aPTT • PTT – Langdell, Wagner and Brinkhous 1953 • aPTT – Proctor and Rappaport – 1961
• Measures a. Time required for fibrin clot to form when a
plasma is incubated with an [ac/vator + par/al thromboplas/n + Ca2+ ]
b. Ac.va.on of the contact factors � PK, HMWK, FXII, FXI
c. Intrinsic pathway factors � FXII, XI, IX, VIII
d. Common pathway � FX, V, II, I
• Prolonged in 1. Deficiencies of all factors except VII and XIII 2. Presence of inhibitors
� Specific inhibitors – FVIII and FIX � Nonspecific inhibitors—LA, Heparin, DTI’s
• Shortened ▫ Elevated FVIII
• Monitor Heparin Therapy
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PL +
ac;vator
Ca2+
Plasma
Fibrinogen • Clauss Technique ▫ Func.onal assay ▫ Fibrinogen concentra.on is inversely
propor.onal to the thrombin .me of diluted plasma
▫ A reference (standard) curve is prepared using known fibrinogen concentra.ons versus their respec.ve thrombin .mes
• Detects ▫ Quan.ta.ve
� Hypofibrinogenemia � Hyperfibrinogenemia
▫ Qualita.ve deficiency � Dysfibrinogenemia
• Acute phase protein à elevated in ▫ Inflamma.on ▫ Trauma ▫ Infec.on ▫ Increases with age ▫ Associated with CVD and thrombosis
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High conctr thrombin
1:10 dilu;on plasma
Fibrinogen • Low levels suggest bleeding ▫ DIC ▫ Thromboly.c therapy
� Results in increased levels of FDP’s (>190 ug/mL) � Interfere with fibrin monomer polymeriza.on
▫ Liver disease � Decreased synthesis of fibrinogen � Abnormal fibrinogen may be seen due to abnormal/increased sialic acid content
▫ Heparin (UFH) may lead to underes.ma.on
• Increased levels ▫ Increasing age ▫ Pregnancy ▫ OCT ▫ Disseminated malignancy
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Thrombin Time / Rep.lase Time Thrombin Time • Measure the conversion of fibrinogen to fibrin • Cleaves fibrinopep.des A and B • Screen for heparin contamina/on • Prolonged ▫ Heparin therapy (UFH) ▫ Hypofibrinogenemia, Dysfibrinogenemia ▫ Paraproteins (Amyloidosis, Myeloma) ▫ Severe LD ▫ Elevated FDP’s ▫ DTI’s ▫ Bovine thrombin glues
Rep.lase .me • Cleaves fibrinopep.de A only
• Unaffected by Heparin • Unaffected by bovine thrombin glues • Same as above
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Fibrin(ogen) Degrada.on Products
• Pa.ent plasma mixed with latex par.cles coated with monoclonal an.-‐FDP an.bodies
• Posi;ve FDP assay indicates ▫ Fibrin and/or fibrinogen is being
degraded by plasmin
• Elevated FDPs ▫ Dysfibrinogenemia ▫ LD, DIC, DVT, PE, MI ▫ Thromboly.c therapy ▫ Primary and secondary
fibrinogenolysis
• What would the D-‐dimer and FSP levels be in a person who has a congenital FXIII deficiency?
• What would the D-‐dimer and FSP levels be in individuals with FXIII deficiency due to DIC?
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D-‐Dimer � Specific product of the degrada.on of fibrin
clots that results from the ac.on of 1. Thrombin
Ø Converted fibrinogen into fibrin clots 2. FXIIIa
Ø Cross-‐linked fibrin monomers clots 3. Plasmin
Ø Cleaved the cross-‐linked fibrin clot
• Monoclonal an.body raised against specific epitopes on D-‐dimer that react with cross-‐linked fibrin ▫ Does not react with
� Fibrinogen degrada.on products � Non-‐cross-‐linked fibrin degrada.on
products ▫ Ensures high specificity for D-‐dimer as a
biomarker of fibrin forma.on and stabiliza.on
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Plasminogen Ac.vators
D-‐Dimers
Fibrin (cross-‐linked)
Plasmin Plasminogen
Thrombin
Fibrinogen Soluble Fibrin + FPA + FPB
XIIIa
D-‐Dimer
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D D e D D
D-‐Dimer
• Monoclonal an.body raised against specific epitopes on D-‐dimer that react with cross-‐linked fibrin ▫ Does not react with
� Fibrinogen degrada.on products
� Non-‐cross-‐linked fibrin degrada.on products
▫ Ensures high specificity for D-‐dimer as a biomarker of fibrin forma.on and stabiliza.on
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Clinical U.lity
• Diagnosis of VTE in combina.on with pretest clinical probability ▫ High nega;ve predic;ve value for exclusion of DVT ▫ Poor posi;ve predic.ve value for DVT
� Elevated in condi.ons unrelated to thrombosis � Almost all pa.ents with acute disease will have elevated D-‐dimer levels
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1. A posi.ve D-‐dimer is NOT specific for VTE 2. Nega.ve D-‐dimer is highly unlikely for VTE 3. The greatest u.lity of D-‐dimer is its nega.ve predic.ve value for VTE!
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Let’s go to the Lab!
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Case 1 • A 5-‐y-‐o girls is seen by her pediatrician. She is an otherwise healthy girls, however her
parents no.ce some easy bruising. • Coagula.on tests were ordered: ▫ PT = 15 sec (9.0-‐12.8) ▫ aPTT = 26.8 sec (23.1 – 34.3) ▫ Fibrinogen = 291 mg/dL (180 – 410) ▫ Thrombin Time = 18 sec (16 – 24)
• What addi.onal ques.ons might you ask? ▫ Repeat the test
� Possibly ▫ Which pathway is involved?
� Extrinsic ▫ Mixing study?
� PT Mix � If it corrects?
▫ Factor assay � FVII � Name?
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Case 2 • A 15-‐y-‐o boy is brought to the ER aner playing soccer with his friends. He
explained that he cut himself in an accident during the game. He bled ini.ally, and the cut stopped bleeding about 3 minutes later. Now it has been 2 hours since the accident and the cut has started bleeding again.
• The physician ordered the following coagula.on tests: ▫ PT = 11.0 sec (9.0-‐12.8) ▫ aPTT = 72.4 sec (23.1 – 34.3) ▫ Fibrinogen = 300 mg/dL (180 – 410) ▫ Thrombin Time = 18 sec (16 – 24)
• What addi.onal ques.ons might you ask? ▫ Which pathway is involved?
� Intrinsic ▫ Mixing study?
� aPTT Mix � If it corrects?
▫ Factor assays � FVIII, IX, XI, XIII � Name?
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Case 3 • A 35-‐y-‐o-‐f is scheduled for surgery and comes in for pre-‐admission tes.ng.
• Coagula.on tests ▫ PT = 18.0 sec (9.0-‐12.8) ▫ aPTT = 72.4 sec (23.1 – 34.3) ▫ Fibrinogen = 300 mg/dL (180 – 410) ▫ Thrombin Time = 18 sec (16 – 24)
▫ Which pathway is involved? � Intrinsic and Extrinsic
▫ Mixing study? � PT and PTT Mix � If both correct?
▫ Factor assays � FX, FV, FII � Name?
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Causes of Bleeding • Primary Hemosta.c Defects ▫ Platelets ▫ Blood vessels
• Secondary Hemosta.c Defects ▫ Factor Deficiencies � < 50% ac.vity ▫ Inhibitor
� Specific � Lupus An.coagulant (global) � Heparin (global)
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Algorithm of Mixing Tests
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Mixing: Pa.ent Plasma + Normal Plasma
Correc.on No Correc.on
Prolonga.on of the Coagula.on Time of the Screening Test
Lupus An.coagulant Specific Factor Inhibitor Factor Deficiency
Mixing Studies • Look for the presence of: ▫ Factor Deficiency versus Inhibitor
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Step 1 Mix and Run Step 2 Mix and Run
TUBE 1
1 mL PNP
TUBE 2 300 uL PNP
300 uL patient plasma
TUBE 3
1 mL patient plasma
TUBE 3
Patient plasma
TUBE 2 300 uL PNP
300 uL patient plasma
TUBE 1
PNP
Run immediately
Run aner 1 hour incuba.on
Incubate @ 37oC
PT / aPTT are normal when the factor levels are 50%
Interpre.ng Mixing Studies
� If the 50/50 corrects aner the immediate and remains corrected aner the 60 minute incuba.on � Factor Deficiency � Follow-‐up with specific factor assays
� If the 50/50 corrects aner the immediate, but prolongs aner the 60 minute incuba.on � Time-‐dependent inhibitor – usually a specific factor inhibitor � ~ 15% of LA’s may be .me-‐and-‐temperature dependent � Follow-‐up with a specific factor assay and specific factor inhibitor assay
� If the 50/50 prolongs aner the immediate and remains prolonged aner the 60
minute incuba.on � Nonspecific inhibitor such as a lupus an;coagulant � Follow-‐up with Lupus an.coagulant assay
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Lupus An.coagulant/APAs
• Lupus An.coagulant ▫ Auto-‐an.bodies directed against phospholipid-‐binding proteins ▫ Targets
� β2GPI—thrombosis � Prothrombin—bleeding � PC, PS, Annexin V—thrombosis
• Paradox ▫ Prolonged cloung .me in vitro ▫ Thrombosis in vivo
YY
Y β2GPI orProthrombin
Membrane
YAntibody:lupus anticoagulantanticardiolipinantiphosphatidylserineanti β2GPIanti Annexin V
ANTIBODY-MEDIATED THROMBOSIS
YY
Y
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dRVVT Screen (Normal plasma)
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Xa
X
Va Xa
Prothrombin
dRVVT
Thrombin Ca2+
Fibrinogen Fibrin
Phospholipid (PF3)
dRVVT Screen (Lupus An.coagulant)
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Xa
X
Va Xa
Prothrombin
dRVVT
Thrombin Ca2+
Fibrinogen Fibrin
Low Phospholipid
Content
dRVVT Confirm (LA)
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Xa
X
Va Xa
Prothrombin
dRVVT
Thrombin Ca2+
Fibrinogen Fibrin
High Phospholipid
Content
Mixing Studies
• 1
• 2
• 3
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Pa;ent 50/50 Mix PNP
50.1 30.2 32.0 immediate
51.0 31.1 31.9 60 minutes
Pa;ent 50:50 Mix PNP
45.0 44.0 30.1 immediate
45.9 51.1 31.2 60 minutes
Pa;ent 50/50 Mix PNP
42.0 31.1 31.1 immediate
43.0 49.8 30.8 60 minutes
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Mixing Studies
PT-pre PT-post
Patient 18.0 18.9
50/50 mix 11.9 12.1
PNP 12.0 12.5
aPTT aPTT
Patient 45.0 45.0
50/50 mix 32.1 33.1
PNP 32.1 32.9
aPTT aPTT
Patient 45.0 45.3
50/50 mix 45.0 62.3
PNP 32.0 33.0
The End
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