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CSMLS > HEM Coag Testing > Flashcards

HEM Coag Testing Flashcards

1
Q

PT (Prothrombin Time): Purpose

A

identifies deficiency in EXTRINSIC + COMMON pathway (fibrinogen, II/ prothrombin, V, VII, X)

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2
Q

The PT reagent contains (3)

A

thromboplastin, phospholipid, and calcium

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3
Q

PTT (Partial Thromboplastin Time): Purpose

A
  • identifies deficiency in INTRINSIC + COMMON pathway (all factors except VII and XIII)
  • monitors unfractioned heparin treatment + some thrombin inhibitors
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4
Q

Mixing Studies: Purpose

A

Determines if abnormal PT/PTT is due to factor deficiency OR an inhibitor

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5
Q

Mixing Studies: Principle

A
  • mix patient plasma + normal control (has all coag factors)
  • test PT or PTT

Corrected = factor deficiency
Uncorrected = perform inhibitor screen

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6
Q

Inhibitor Screen: Purpose

A

Determines if inhibitor is immediate OR delayed

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7
Q

Inhibitor Screen: Principle

A
  • (In 1:1 AND 4:1 patient ratios) = mix patient plasma + Normal control (has all coag factors)
  • test PT/ PTT 3 times:
    1. Mixed: Immediately
    2. Mixed: after 1 HOUR of incubation at 37 degrees
    3. Separately: after 1 HOUR of incubation at 37 degrees
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8
Q

What does it mean if PT/PTT of an inhibitor screen is prolonged immediately after patient plasma + Normal control are mixed ?

A
  • Inhibitor screen = POS
  • Inhibitor reacts IMMEDIATELY
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9
Q

What does it mean if PT/PTT of an inhibitor screen is prolonged after 1 HOUR of (patient plasma + Normal control) being mixed when it was normal after being immediately mixed ?

A
  • Inhibitor screen = POS
  • Inhibitor is delayed reacting
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10
Q

How can heparin be removed before performing an inhibitor screen ? Why is this done ?

A
  • remove Heparin using Hepzyme
  • Heparin causes FALSE POS inhibitor screen
  • prolongs PT/ PTT
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11
Q

Why is patient plasma and Normal control incubated SEPARATELY for 1 hour at 37 degrees as part of the Inhibitor Screen ? What should the results be ?

A
  • separate incubation ensures clotting factors did not degrade during incubation
  • Normal control = POS
  • patient plasma = neg
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12
Q

Why does the inhibtor screen use 1:1 AND 4:1 patient to Normal control ratios ?

A

4:1 ratio increases sensitivity to inhibitors

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13
Q

Single Factor Assay: Purpose

A

Determines which factor(s) patient is deficient in

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14
Q

Single Factor Assay: Principle

A
  • mix patient plasma + plasma deficient in a single factor
  • test PT or PTT
  • compare results to standard graph to determine factor concentration
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15
Q

If patient plasma corrects PT/ PTT in a Single Factor Assay, what does this mean ?

A

Recall: patient plasma + plasma deficient in a known factor are mixed

Corrected = patient corrects deficient plasma; patient is not deficient in particular factor

Uncorrected = patient unable to correct deficient plasma; patient is deficient in the same known factor

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16
Q

Fibrinogen Testing: Purpose

A

Determines levels of fibrinogen in plasma

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17
Q

Fibrinogen Testing: Principle

A
  • EXCESS thrombin + patient sample
  • level of plasma fibrinogen is INVERSELY proportional to clotting time

NOTE: excess thrombin neutralizes anti-thrombin activity (FDPs)

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18
Q

Why is thrombin added in EXCESS in fibrinogen testing ?

A

To neutralize anti-thrombin activity (ie. FDPs)

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19
Q

TT (Thrombin Time): Purpose

A
  • Detect DECREASED levels of fibrinogen, DYSFIBRINOGENEMIA, or THROMBIN INHIBITORS (ie. FDPs, D-dimers)
  • Monitor/ evaluate DIC, heparin therapy, fibrinogen diseases
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20
Q

TT: Principle

A

Thrombin Time:
- dilute BOVINE thrombin + patient sample to bypass previous steps of coag cascade
- measures time to convert fibrinogen to insoluble fibrin crosslinks

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21
Q

D-Dimer: Purpose

A

To rule out DIC

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22
Q

D-Dimer: Principle

A
  • turbidimetric IMMUNOASSAY (DIRECTLY proportional)
  • MONOCLONAL Abs specific to D-dimers coat latex particles
  • D-dimers DIRECTLY bind to Abs = AGGLUTINATION = increased turbidity = INCREASED ABSORBANCE measured
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23
Q

Reptilase Time: Purpose

A

To detect HEPARIN, DYSFIBRINOGENEMIA, or FIBRINOGEN DEFICIENCY

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24
Q

Reptilase Time: Principle

A

reptilase (enzyme) = converts fibrinogen to fibrin + NOT INHIBITED by heparin = clot forms
- compares results to PROLONGED thrombin time (TT)

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25
Q

What does it mean if TT = prolonged and Reptilase Time = equally prolonged ?

A

Fibrinogen Deficiency
- there is no fibrinogen in the first place; reptilase cannot form fibrin

NOTE = prolonged TT cannot be due to heparin because reptilase is not affected by heparin, which is also prolonged in this case

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26
Q

What does it mean if TT = prolonged and Reptilase Time = MORE PROLONGED ?

A

DYSFIBRINOGENEMIA

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27
Q

What does it mean if TT = prolonged and Reptilase Time = NORMAL ?

A

HEPARIN is present
- but reptilase is unaffected by the anticoagulant

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28
Q

Which coagulation tests use Turbidimetric end-point clot detection ?

A
  • PT
  • PTT
  • TT
  • Fibrinogen
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29
Q

Platelet Aggregometry: Purpose

A

To assess PLT function (secretion, aggregation, adhesion w/ ristocetin)

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30
Q

Platelet Aggregometry: Principle

A
  • DO NOT DO if PLT <50 x10^9/L
  • PLT-RICH plasma is stirred in AGGREGOMETER with diff agonists:
    1. ADP + collagen + EPO + arachidonic acid = tests GPIIb/ IIIa and fibrinogen function
    2. Ristocetin = tests GPIb and vWF function

NOTE: agonists initiate PLT aggregometry

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31
Q

Interferences in PLT Aggregometry

A
  • gross lipemia
  • aspirin
  • PLT <50 x10^9/L
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32
Q

Ristocetin Co-factor Assay: Purpose

A
  • To ensure vWF is present for coagulation
  • Differentiate VonWillebrand Disease from Bernard Soulier
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33
Q

Ristocetin Co-factor Assay: Principle

A
  • mix patient plasma with Normal PLTs + Ristocetin
  • Ristocetin induces vWF to attach to GPIb receptors on Normal PLTs = aggregation
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34
Q

How to differentiate Unfractioned Heparin (UFH) from Low Molecular Weight Heparin (LMWH) ?

A

Both:
- indirect anticoagulants

UFH:
- inhibits all serine proteases (plasmin, IIa, IXa, Xa, XIa, XIIa) EXCEPT VII and Kallikrein
- monitored by aPTT or anti-Xa assay

LMWH:
- inhibits Xa
- monitored by anti-Xa assay ONLY

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35
Q

Heparin is a cofactor of __.

A

Heparin is a cofactor of ANTI-THROMBIN.

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36
Q

Tube/ anticoagulant requirements for coagulation testing ?

A
  • Sodium citrate (light blue top)
  • Filled to capacity
  • 1:9 anticoagulant to blood
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37
Q

Why is Sodium Citrate the preferred anticoagulant for coagulation testing ?

A
  1. Preserves V and VIII (labile factors)
  2. Stabilizes pH
  3. Does not inhibit PLT function
  4. Anticoagulant reversed when Ca2+ is added
38
Q

Interferences in Coagulation Testing

A
  • clotted samples
  • insufficient tube volume
  • EDTA collection
  • anticoagulants therapy (heparin, coumadin)
  • hemolysis
  • lipemia
  • cold temp
  • hot temp
39
Q

How does cool temp storage interfere with coag testing ?

A

prematurely activates VII and PLTs during transport/ storage

40
Q

How does hot temp interfere with coag testing ?

A

deteriorates factors V and VIII (heat-labile)

41
Q

How does gross lipemia interfere with coag testing ?

A

interferes with testing that use end-point detection (PT, PTT, TT, Fibrinogen)
- increase turbidity = falsely decrease

42
Q

How does EDTA interfere with coag testing ?

A
  • EDTA does not preserve factor V
  • prolongs tests
  • chelates Ca2+ needed for coagulation cascade
43
Q

How does insufficient tube volume interfere with coag testing ?

A

too much Sodium Citrate anticoagulant = tests falsely prolonged

NOTE: High Hct will have less plasma

44
Q

How does Turbidimetric End-point detection work in coag testing ?

A
  • fibrin clot forms = optical density increases/ transmittance decreases
  • when optical density > baseline = timer stops to indicate cot formation
45
Q

How does hemolysis interfere with coagulation testing ?

A
  • severe hemolysis = falsely decrease PT and PTT
  • coagulation prematurely starts before testing
  • check clots in hemolyzed samples
46
Q

How to differentiate DIC from TTP and HUS

A

DIC:
Transfusion history
PBS = poly, schisto, NO SPHERO, nRBC
PT/ PTT = PROLONGED
Fibrinogen = decreased (clot formation)
D-dimer = increased (fibrinolysis)

NOTE: all will have decreased PLT, (PBS = poly, schisto)

47
Q

What is Bernard Soulier Syndrome ?

A

Deficient/ defective GPIb from PLT surface
- PLTs cannot bind vWF = DEFECTIVE ADHESION

48
Q

Bernard Soulier Syndrome (PBS, BM, PT/PTT. PLT, BT, PLT aggregation)

A

PBS= giant PLTs
BM= normal/ increased megakaryocytes
PT/ PTT = normal
PLT = mild DECREASE
BT= increased (defective adhesion)

PLT aggregation:
ADP, EPO, collagen, a.a.= normal
Ristocetin= ABNORMAL

49
Q

What is Glanzmann’s Thrombasthenia

A

GPIIb/ IIIa deficient or defective
- PLTs cannot bind fibrinogen and vWF = DEFECTIVE AGGREGATION

50
Q

Glanzmann’s Thrombasthenia (PBS, BM, PT/ PTT, PLT, BT, PLT aggregation)

A

PBS/ BM= normal PLTs and megakaryocytes
PT/PTT= normal
BT= increased (defective aggregation)

ADP, EPO, collagen, a.a.= abnormal
Ristocetin= normal

51
Q

What is vWD ?

A

mutation of vWF gene= quantitative/ qualitative defect
- DEFECTIVE PLT ADHESION

52
Q

vWD (PT, PTT, PLT, BT, PLT aggregation). What other tests can be done ?

A

PT = normal
PTT = normal OR increased
PLT= normal
BT= increased (defective adhesion)

ADP, collagen, EPO, a.a.= normal
Ristocetin= abnormal

vWF antigen assay= decreased
FVIII assay = decreased (vWF needed to stabilize FVIII in plasma)

53
Q

vWD vs Bernard Soulier: Ristocetin cofactor assay results

A

vWD= abnormal (no vWF)
Bernard Soulier= normal (has vWF to bind GPIb receptors supplied by normal PLTs)

RECALL: Ristocetin cofactor assay tests patient plasma with NORMAL PLTs

54
Q

How does liver disease affect coagulation ?

A

Affects factors synthesized in liver:
- vit K dependent factors (II/ prothrombin, VII, IX, X, Protein C/S/Z)
- Dysfibrinogenemia

55
Q

Hemophilia A: cause and lab results (factor assay, PT, PTT, TT, BT)

A
  • FVIII deficiency
  • X-linked recessive

FVIII assay = decreased
PT= normal
PTT= abnormal
TT= normal
BT= normal

56
Q

Hemophilia B: cause and lab results (factor assay, PT, PTT, BT, TT)

A
  • Factor IX deficiency

FIX assay= DECREASED
PT= normal
PTT= INCREASED
BT= normal
TT= normal

57
Q

Hemophilia C: cause and lab results (factor assay, PT, PTT, BT, TT)

A
  • FXI deficiency

FXI assay= DECREASED
PT= normal
PTT= INCREASED
TT = normal

58
Q

FVII deficiency: lab results (PT, PTT, TT, BT)

A

PT= INCREASED
PTT, TT, BT= normal

59
Q

Factors II, V, X deficiency: lab results (PT, PTT, TT, BT)

A
  • all are factors in common pathway

PT/, PTT= increased
TT, BT= normal

60
Q

Lupus Anticoagulant Syndrome: cause and clinical effects

A
  • anti-phospholipid autoAb form = bind to phospholipids (PF3) in PTT reagent = interferes with prothrombin activation
  • PROLONGS COAG TESTING
61
Q

Lupus Anticoagulant Syndrome: lab results (PT, PTT, TT, Mixing Studies, DRVVT)

A

PT= normal
PTT= INCREASED
TT= normal
Mixing studies= no correction with normal plasma
DRVVT= POSITIVE

DRVVT= Dilute Russel Viper Venom Time

62
Q

DRVVT: principle

A
  • viper venom activates factor X
  • reagent has low [phospholipid]

PROLONGED/ POSITIVE= Lupus Anticoagulant (LAC) in patient plasma interferes with prothrombin activation

Normal= no LAC

63
Q

Follow-up testing after POSITIVE DRVVT

A
  1. Use reagent with EXCESS PHOSPHOLIPIDS to neutralize LAC = normal clotting time = LAC positive
  2. Mixing study 1:1 of patient plasma and Normal plasma = uncorrected = LAC positive
64
Q

Which of the following would lead to a prolonged bleeding time?

a.
A platelet count of 155 x 10^9/L

b.
Von Willebrand disease

c.
Fibrinogen value of 1.2 g/L

d.
Hemophilia A

A

b.
Von Willebrand disease

NOTE: primary hemostasis is affected

65
Q

Prolonged PT and PTT: DIC, primary/ hyper fibrinoloysis, both or neither ?

A

DIC and hyper/primary fibrinoloysis

66
Q

Increased D-dimers: DIC, primary/ hyper fibrinoloysis, both or neither ?

A

DIC and hyper/primary fibrinoloysis

67
Q

Elevated plasmin: DIC, primary fibrinoloysis, both or neither ?

A

DIC and hyper/primary fibrinoloysis

68
Q

Platelet count is normal: DIC, primary/ hyper fibrinoloysis, both or neither ?

A

ONLY hyperfibrinolytic states (primary fibrinolysis)

69
Q

Schistocytes can be seen on the smear: DIC, primary fibrinoloysis, both or neither ?

A

ONLY Disseminated Intravascular Coagulation (DIC)

70
Q

Fibrinogen degradation products are elevated: DIC, primary fibrinoloysis, both or neither ?

A

Both

71
Q

Which of the following is true about the aPTT test?

a.
It will be abnormal with a factor XIII deficiency

b.
It is used to monitor coumadin therapy

c.
It will be prolonged with abnormal platelet function

d.
It will be prolonged in Von Willebrand deficiency

A

d.
It will be prolonged in Von Willebrand deficiency

72
Q

Thrombocytopenia on PBS: HUS, TTP, both or neither ?

A

Both

73
Q

Microangiopathic hemolytic anemia with schisto and poly: HUS, TTP, both or neither ?

A

Both

74
Q

Clotting factors are decreased (used up): HUS, TTP, both or neither ?

A

Neither

75
Q

Toxins damage renal glomerular capillaries: HUS, TTP, both or neither ?

A

ONLY Hemolytic Uremic Syndrome (HUS)

76
Q

Abnormally large vWF multimers are implicated: HUS, TTP, both or neither ?

A

ONLY Thrombotic Thrombocytopenic Purpura (TTP)

77
Q

Autoantibodies to ADAMTS 13 can occur: HUS, TTP, both or neither ?

A

ONLY Thrombotic Thrombocytopenic Purpura (TTP)

78
Q

Prolonged PT and APTT: HUS, TTP, both or neither ?

A

Neither

79
Q

Which of the following can cause a prolonged APTT?

a.
Decreased levels of factor XIII

b.
Decreased levels of factor VII

c.
Decreased levels of factor XI

d.
In-vitro hemolysis

A

c.
Decreased levels of factor XI

80
Q

Crit: PLT

A

inpatient: <10 x10^9/L
outpatient: <20 x10^9/L

81
Q

Crit: PTT

A

> 120 sec

82
Q

Which statement about the fibrinogen assay is most correct?

a.
Clotting time is proportional to the amount of thrombin in the plasma

b.
An abnormal result is seen in patients on heparin therapy

c.
Concentrated thrombin reagent is added to dilute plasma

d.
Patient plasma is mixed 1:1 with fibrinogen-deficient plasma

A

c.
Concentrated thrombin reagent is added to dilute plasma

83
Q
  1. Mode of action of heparin as an anticoagulant in the human body
  2. List which coagulation factors are inhibited by UFH
A
    • Heparin is a cofactor for Antithrombin
    • Heparin binds to AT, changes its conformation, and accelerates the rate of inactivation of coagulation factors by AT
  2. UFH inhibits all the serine proteases except VII and Kallikrein
    - serine proteases: XIIa, XIa, IXa, Xa and IIa (and plasmin)
84
Q

Thrombocytosis is typically seen in which of the following?

a.
Acute leukemia

b.
Post-splenectomy

c.
Essential Thrombocythemia

d.
Ineffective thrombopoiesis

A

b.
Post-splenectomy

c.
Essential Thrombocythemia

85
Q

A patient specimen is received from an outside laboratory for coagulation testing. The history provided indicates the patient is on Coumadin (warfarin). The following results are obtained:

PT: no clot detected

PTT: no clot detected

The specimen is retested and the results check. You bring the results to your supervisor, who instructs you to perform a fibrinogen assay. Will the fibrinogen assay be useful?

A

Yes. A fibrinogen assay would be useful. The patients history indicates coumadin therapy and coumadin acts by inhibiting fibrinogen function

86
Q

Which clotting factors would be affected by coumadin therapy? Select all that apply:

a.
Factor XIII

b.
Factor V

c.
Factor VIII

d.
Factor IX

A

d.
Factor IX

87
Q

How is the fibrinogen concentration of a sample determined in the fibrinogen assay?

A

The instrument compares the clotting time to a calibration curve

88
Q

Which statement about the quantitative D-dimer assay is correct?

a.
The normal reference range is >0.5 g/L

b.
The result is abnormal when FDP’s are decreased

c.
Micro-latex particles in the reagent are coated with monoclonal antibodies to D-dimer

d.
The presence of D-dimers is detected by clot formation

A

c.
Micro-latex particles in the reagent are coated with monoclonal antibodies to D-dimer

89
Q

In the APTT test, what happens during the initial incubation after the APTT reagent is added to the test plasma?

a.
Factor VII and the extrinsic pathway are activated

b.
Factors IX and VIII are activated

c.
Factor XI and XII are activated

d.
Factor X and V are activated

A

c.
Factor XI and XII are activated

90
Q

Which of the following is correct with respect to specimen collection for coagulation testing?

a.
Mix the sample well with vigor

b.
Draw coagulation specimens after an EDTA tube

c.
Use a 1:9 dilution of anticoagulant to blood

d.
Make sure the vacutainer tube is filled 70% capacity

A

c.
Use a 1:9 dilution of anticoagulant to blood

91
Q

Follow-up for Hct > 0.55 L/L

A
  • there is excess anticoagulant = extra citrate will bind the calcium in the test reagent and falsely prolong clotting times
  • specimen should be recollected with less anticoagulant and the tests repeated

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