Coagulation > Coagulation Testing > Flashcards

Coagulation Testing Flashcards

(40 cards)

Study These 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 ?

Study These Flashcards
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 ?

Study These Flashcards
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)?

Study These Flashcards
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?

Study These Flashcards
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?

Study These Flashcards
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 ?

Study These Flashcards
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 ?

Study These Flashcards
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 ?

Study These Flashcards
A
  • Chromogenic assay
  • Protein C activity decreased in :
    • Warfarin therapy, Vitamin K deficiency
    • Liver disease
    • Ongoing extensive thrombosis
    • DIC
    • Hereditary deficiency
25
How is protein S measured ?
* 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
What situations can decrease the protein S levels as well as the protein S activity ?
* 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
How is the Lupus inhibitor assay performed ?
* 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
How is the activated protein C resistance assay performed ?
* 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
How is the vWF antigen assay performed ?
* quantitative automated latex immunoassay
30
How is vWF factor function evaluated ?
* 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
How is the vWF collagen binding assay performed ?
* 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
How are the vWF multimers evaluated ?
* 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
What lab values should make you think that the sample has been heparinized ?
* PTT and TT are prolonged * this is also the pattern seen with a direct thrombin inhibitor
34
What can cause a prolonged PT and normal PTT ?
* deficiency or inhibitor of Factor 7 * early Warfarin therapy (Factor 7 falls first) * Atypical Lupus inhibitor
35
What can cause a prolonged PTT and a normal PT ?
* Lupus inhibitor * deficiency or inhibitor of Factor 8, 9, 11, or 12 or contact phase
36
What can cause prolongation of both PT and PTT ?
* Warfarin therapy, Vitamin K deficiency, liver disease * Deficiency or inhibitor to: Factor 2, 5, or 10 * Thrombin inhibitor * Fibrinogen deficiency
37
What causes a prolonged Thrombin time ?
* 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
What are the uses for Fibrinogen assays ?
* diagnosis of dysfibrinogenemia and hypofibrinogenemia * diagnosis of DIC, liver failure and primary fibrinolysis * guiding transfusion therapy with cryoprecipitate or NovoSeven
39
What is the definition of a Bethesda unit ?
* 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
What are the specimen transport and handling conditions often required for coagulation testing?
* 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
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