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Coagulation > Coagulation Testing > Flashcards

Coagulation Testing Flashcards

1
Q

What does PT measure ?

A
  • measures the extrinsic clotting system and the common pathway
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2
Q

What does PTT measure ?

A
  • measures the intrinsic pathway and common pathway
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3
Q

What does thrombin time measure ?

A
  • TT measures conversion of fibrinogen to fibrin polymer.
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4
Q

What is a requirement of

coagulation testing ?

A
  • must have citrated platelet poor plasma
  • this will help prevent coagulation from being initiated because you remove the phospholipid and the calcium

read p. 71 principles of performance

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5
Q

Many coagulation assays are clot-detection based,

what are some of the down sides of using an optical detection method ?

A
  • optical instruments suffer from more interference by lipemia, icterus and hemolysis
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6
Q

What factor deficiencies is PT sensitive to ?

A
  • decreased levels of factors VII, X, V, II and fibrinogen
  • Frequently used to monitor Wafarin therapy
  • Started by adding Thromboplastin
    • Tissue factor plus phospholipid
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7
Q

What is the time frame that PT/INR testing

may be performed ?

A
  • may be done up to 24 hours from the time of collection
  • sample must be uncentrifuged or centrifuged with plasma remaining on top of the cells
  • must be stored at 2-4 deg C or at room temp
  • if testing can’t be done in 24 hours
    • plasma must be removed from cells and frozen at -70 deg C
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8
Q

What factors is the PT most and least

sensitive to ?

A
  • Most sensitive: Factor VII
  • Least sensitive: Factor II (prothrombin) and and fibrinogen

Note: most instruments have a Heparin neutralizing substance for the PT (such as polybene) in order to decrease the effect of Heparin. Also want minimal sensitivity to lupus anticoagulants.

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9
Q

When there is a strong lupus

anticoagulant that interferes with the PT in a patient on

oral anticoagulation, what test is appropriate to monitor response to the oral anticoagulant ?

A
  • Chromogenic factor X assay
    • should be used to monitor the response to the oral anticoagulation assay.
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10
Q

What is the ISI value in terms of determination

of the INR ?

A
  • it is an experimentally determined value indicating the sensitivity of the thromboplastin to Warfarin induced factor deficiencies.
    • Vitamin K dependent factors
  • this value may be specific for instrument and reagent combinations
  • use the geometric mean when the population is skewed
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11
Q

What factor levels would significantly

prolong the PT ?

A
  • Factors VII, V, or X : < 40%
  • Fibrinogen : < 100 mg/dL
  • Prothrombin : < 30%
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12
Q

What is the starter for aPTT and what

does the test monitor ?

A
  • partial thromboplastin
    • cephalin or phosphatide
  • measure the intrinsic and common coagulation pathways
    • screen/monitor inherited or acquired coagulation disorders
    • monitor unfractionated heparin therapy
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13
Q

What factor deficiencies is aPTT less sensitive to

and what can it detect ?

A
  • less sensitive to VII and XIII (cannot detect deficiencies of these)
  • aPTT usually normal if all coagulation factors have a concentration of 30%
  • aPTT is prolonged in:
    • Heparin therapy
    • Direct thrombin inhibitors
    • Specific factor inhibitors
    • Lupus-like anticoagulants
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14
Q

How are aPTT values in newborns different

from adult values ?

A
  • newborns have a prolonged aPTT
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15
Q

What can cause a shortened aPTT?

A
  • pre-analytical activation of clotting factors (difficult venipuncture)
  • hypercoagulability
    • cancer, MI
    • hyperthyroidism
    • diabetes
    • pregnancy
  • acute phase reactants
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16
Q

What are some pre-analytical variables that

can affect aPTT and sometimes PT ?

A
  • prolonged aPTT
    • blood drawn from catheter that was flushed with Heparin
    • underfilled collection tube
  • prolonged PT and aPTT
    • polycythemic samples - excess citrate to plasma ratio
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17
Q

What does thrombin time measure ?

A
  • assesses fibrinogen activity in plasma
  • measures the time for clot formation when thromin is added to citrated plasma
18
Q

What can prolong the aPTT ?

A
  • Heparin therapy or sample contamination (Hep lock, IV line)
  • Lupus anticoagulant
  • Hereditary or acquired deficiency
  • Severe liver disease
  • Factor or assay inhibitors
  • Contact system deficiency (not associated with bleeding), Factor 12, HMWK, Pre-Kallikrein
19
Q

What can prolong the thrombin time (TT)?

A
  • test is sensitive to heparin and fibrinogen
  • Prolonged in:
    • heparin therapy or contamination
    • severe fibrin or fibrinogen degradation (DIC)
    • dysfibrinogenemia
    • thrombin inhibitor:
      • lepirudin
      • drugs
      • antibodies
20
Q

How does the

Platelet function analyzer (PFA) work?

A
  • whole blood is drawn through a drug coated opening
    • Collagen/Epinephrine
    • Collagen/ADP
  • measure the time to occlusion of the orifice
21
Q

What can increase the PFA

closure times?

A
  • Thrombocytopenia
  • Anemia
  • Antiplatelet drugs
  • von Willebrand disease
  • other hereditary or acquired platlet dysfunction
22
Q

What is the mechanism of the antithrombin

activity assay and what is it measuring ?

A
  • measures antithrombin activity
  • Chromogenic substrate assay (anti-IIa assay)
  • plasma gets diluted in a heparin buffer and excess thrombin (IIa) is added
    • residual thrombin is measured with a chromogenic substrate
    • difference between original and final is equal AT activity
23
Q

What conditions can decrease

antithrombin activity ?

A
  • Heparin therapy
  • ongoing or extensive thrombosis
  • systemic coagulation activation (DIC)
  • nephrotic syndrome
  • Hereditary deficiency
  • Aspariginase therapy
24
Q

What is the methodology for measuring

Protein C activity and what can

decrease Protein C activity ?

A
  • Chromogenic assay
  • Protein C activity decreased in :
    • Warfarin therapy, Vitamin K deficiency
    • Liver disease
    • Ongoing extensive thrombosis
    • DIC
    • Hereditary deficiency
25
Q

How is protein S measured ?

A
  • Screen with Free Protein S antigen
    • Quantitative immunoassay
  • Protein S activity

note:

  • there is interference from elevated levels of Factor VIII (falsely low S), and thrombin inhibitors like Lepirudin (falsely high S)
26
Q

What situations can decrease the protein S levels

as well as the protein S activity ?

A
  • Warfarin therapy
  • Vitamin K deficiency
  • Liver disease
  • ongoing or extensive thrombosis
  • systemic coagulation (DIC)
  • pregnancy
  • Inflammatory syndromes due to increase in C4B biniding protein
  • Hereditary deficiency
27
Q

How is the Lupus inhibitor assay

performed ?

A
  • perform a lupus sensitive PTT with and without addition of excess hexagonal phase phospholipid
  • calculate the difference in clotting time with and without hexagonal phospholipid
28
Q

How is the activated protein C

resistance assay performed ?

A
  • PT based assay
  • using Factor V activation and inhibition by APC
  • Calculate the ratio with and without APC added
    • Reduced ratio indicates APC resistance
      • Factor V Leiden
29
Q

How is the vWF antigen assay performed ?

A
  • quantitative automated latex immunoassay
30
Q

How is vWF factor function evaluated ?

A
  • enzyme immunoassay
  • antibody is directed to the functional site on vWF
  • Highly correlated with Ristocetin cofactor assay
  • Type 1: reduction in parallel with vWF antigen
  • Type 2: greater reduction than vWF antigen
31
Q

How is the vWF collagen binding assay performed ?

A
  • collagen coated plate, plasma vWF binds to collagen
    • bound vWF detected with anti-vWF antibody
  • Type 1: reduction in parallel with vWF antigen
  • Type 2: greater reduction than vWF antigen
32
Q

How are the vWF multimers evaluated ?

A
  • uses a western blot assay of the von willebrand factors
  • Type 2A: loss of intermediate and high MW multimers, abnormal forms
  • Type 2B: loss of high MW multimers, normal pattern
33
Q

What lab values should make you think that the

sample has been heparinized ?

A
  • PTT and TT are prolonged
  • this is also the pattern seen with a direct thrombin inhibitor
34
Q

What can cause a prolonged PT and normal PTT ?

A
  • deficiency or inhibitor of Factor 7
  • early Warfarin therapy (Factor 7 falls first)
  • Atypical Lupus inhibitor
35
Q

What can cause a prolonged PTT and a normal PT ?

A
  • Lupus inhibitor
  • deficiency or inhibitor of Factor 8, 9, 11, or 12 or contact phase
36
Q

What can cause prolongation of both PT and PTT ?

A
  • Warfarin therapy, Vitamin K deficiency, liver disease
  • Deficiency or inhibitor to: Factor 2, 5, or 10
  • Thrombin inhibitor
  • Fibrinogen deficiency
37
Q

What causes a prolonged Thrombin time ?

A
  • Hypofibinogenemia (usually <90)
  • Dysfibrinogenemia
  • The presence of fibrin or fibrin split products that block the conversion of fibrinogen to fibrin
  • unfractionated Heparin
    • LMW Heparin usually does not cause prolonged TT
  • Presence of thrombin inhibitors
  • Presence of high immunoglobulins which can prevent fibrin formation

Note: if PTT is prolonged, can obtain a TT to rule out or rule in Heparin contamination

38
Q

What are the uses for Fibrinogen assays ?

A
  • diagnosis of dysfibrinogenemia and hypofibrinogenemia
  • diagnosis of DIC, liver failure and primary fibrinolysis
  • guiding transfusion therapy with cryoprecipitate or NovoSeven
39
Q

What is the definition of a Bethesda unit ?

A
  • quantity of inhibitor that neutralizes 50% of the Factor VIII in normal plasma in 2 hours
  • quantification of the Bethesda assay –> serial dilutions to help identify an inhibitor level to a factor
  • low titer: 0.5 to 5 BU
  • high titer: > 5 BU
40
Q

What are the specimen transport and handling conditions

often required for coagulation testing?

A
  • transported at temps 15-22 deg C
    • too cold of temperatures can activate platelets and the clotting cascade
    • too hot of temperatures can degrade the clotting factors
  • For plasma based testing:
    • plasma should be separated within 4 hours of sample draw
  • For Heparin activity testing
    • 1 hour requirement for plasma separation
  • Plasma should be separated for most coagulation tests
    • platelets can activate coagulation
    • must double centrifuge for Lupus anticoagulant testing
  • Repeat freeze-thaw events may result in loss of Factor VIII and Factor V testing

Coagulation (17 decks)

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