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hemostasis > section 8 - testing methods > Flashcards

section 8 - testing methods Flashcards

1
Q

list mechanisms of coagulation instrumentation

A
  • mechanical
  • photo-optical (turbidometric)
  • nephelometric
  • chromogenic
  • immunologic
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2
Q

describe mechanical clot detection

A
  • electro: two probes, clot completes the circuit = stop timer
  • magnetic: less movement of steel ball = breaks contact with magnetic sensor when clot forms
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3
Q

describe photo-optical/turbidimetric principle of coagulation testing

A

measures change in optical density (light transmittance) through a sample
- less light = stop timer = clot formed

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4
Q

describe nephelometric coagulation instrumentaitn

A
  • antibody-antigen complex precipitates causing turbidity that scatters light
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5
Q

describe chromogenic coagulation instrumentation

A
  • based on color changing substance pNA
  • protein protease frees pNA
  • intensity is proportional to protease activity
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6
Q

describe immunologic coagulation instrumentation

A
  • antigen-antibody reactions w/ coated Ab microlatex
  • particles agglutinate and absorb light equal to amount of Ag present
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7
Q

what factors are measured in PT

A
  • VII, X, V, II and I
  • adequacy of the extrinsic pathway
  • cannot measure the alternative pathway
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8
Q

what is in the PT reagent

A
  • thromboplastin: TFIII, PFIII and Ca
  • can contain a heparin inhibitor
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9
Q

reference range of PT

A

11-13 seconds

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10
Q

how do oral anticoagulants impact PT

A
  • used to monitor effects
  • should have a PT of 20-27
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11
Q

define INR

A
  • international normalized ratio
  • correction standardizes patient PT between laboratories
  • measures PIVKA (vit K factors) effect on PT
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12
Q

how does the ISI relate to INR

A
  • ISI is the defined sensitivity of individual reagents
  • reference thromboplastin has a value of 1
  • further ISI of a reagent is from 1, the less sensitive to PIVKA (vit K nonfunctional factors)
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13
Q

INR calculation and reference range

A

INR= (patient PT/normal PT) ^ ISI
- reference: 0.9-1.2 (not taking coumadin)
- therapeutic reference range: 2.0-3.0

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14
Q

what does the APTT measure

A
  • adequacy of intrinsic pathwaya
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15
Q

how is APTT measured

A
  • activator reagent for contact factors, PF3 and Ca
  • activator reagent + PPP –(warmed)–> add Ca –> time to clot
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16
Q

APTT reference range

A

26-36 seconds

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17
Q

what is the APTT used for

A

intrinsic pathway adequacy and effects of heparin
- heparin patients = 1.5-2.5 times normal value

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18
Q

describe the thrombin time test (TT)

A
  • adequacy of fibrinogen
  • reagent = dilute thrombin
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19
Q

how is TT measured

A

PPP + 100 micro liters thrombin reagent

20
Q

TT reference range

A

14-20 seconds

21
Q

describe the purpose of a 50:50 mix

A

if PT, APTT or TT is prolonged = it determines if it is due to deficiency or inhibitor
- normal plasma and patient plasma in a 1:1 ratio

22
Q

what causes a prolonged PT/APTT or TT if a 50:50 mix corrects the time to clot

A

factor deficiency
- normal plasma is supplying the deficient factor

23
Q

what causes a prolonged PT/APTT or TT if a 50:50 test does not fix the prolonged time

A

due to inhibitor
- inhibitor also inhibits normal plasm

24
Q

describe the immunological fibrinogen assay

A
  • RID or nephelometry
  • quantitates total fibrinogen including dysfunctional
25
Q

describe the fibrinogen activity assay

A
  • mechanical or photo-op method
  • quantitates functional fibrinogen
  • most common assay
26
Q

describe the fibrinogen assay

A
  • quantitates fibrinogen activity only functional fibrinogen
  • similar to TT but plasma diluted 1:10 w/ thrombin added each time
  • used standard curve to convert mg/dL of fibrinogen
27
Q

reagents in fibrinogen assay

A
  • fibrinogen calibration reference
  • thrombin
  • owrens veronal buffer (diluent)
28
Q

reference range for fibrinogen assay

A

200-450 mg/dL

29
Q

describe D-Dimer assay

A
  • present only in fibrinolysis
  • all assays use monoclonal Ab
  • ELISA/ELFA and latex agglutinattion most common -> OD, fluorescence or visible agglutination
30
Q

D-Dimer interpretation

A
  • if no agglutination test is reported as <0.5 ug/mL never 0
  • see in cases of active thrombosis
    -> DIC
    -> DVT
    -> PE
31
Q

describe the priciniple of the factor assay

A
  • used when PT or APTT is prolonged to determine which factor is missing
  • specific factor deficient plasma and pt plasma
    -> if remains prolonged = deficient
    -> if fixed = not the problem
32
Q

what is the % activity of factor

A

using dilutions of normal plasma and deficient plasma see how active the factor is
- read % activity off of the curve

33
Q

reference range for factor acvitity

A

60-150%

34
Q

describe the anti-Xa assay

A
  • monitors LMW heparin, UFH or direct Xa inhibitors
  • chromogenic assay
  • add pt plasma + reagent (constant Xa) + chromogenic = degree of color is inversely proportional to amt AT in sample
35
Q

describe the russell viper venom time (RVVT)

A
  • venom is a direct activator of factor X
  • measures common pathway
  • reference range 20-30 seconds
36
Q

RVVT reference range

A

20-30 seconds

37
Q

describe the reptilase time test

A
  • reptilase cleaves only fibrinopeptide A from fibrinogen (enough to start clotting)
  • not inhibited by thrombin inhibitors (heparin)
  • differentiates deficiency of fibrinogen from inhibitor
  • RR: 16-22 seconds
38
Q

reference range of reptilase time (RT)

A

16-22 seconds

39
Q

what is the issue if TT is prolonged but RT is normal

A

thrombin inhibitor, not fibrinogen deficiency

40
Q

what is the issue if TT and RT is prolonged

A

fibrinogen deficiency or FDPs present in high amounts

41
Q

describe the Urea Clot lysis (urea solubility)

A
  • determines adequacy of FXIII
  • clot formed with PRP and Ca in glass tube -> 5 M urea added -> see if clot dissolves
  • if clot dissolves = inadequate FXIII
42
Q

describe the euglobulin clot lysis test

A
  • qualitative measure of pt endogenous fibrinolytic capability
  • monitors fibrinolytic activity of tPA medicine pt
  • check fibrinogenolysis amount
43
Q

euglobulin clot lysis procedure

A
  • euglobulin = plasminogen, plasmin/plasmin activators and fibrinogen
  • euglobulin fraction precipitated in acetic acid
  • precipitate recovered and resolubilized in buffer
  • fibrinogen is added to clot
  • watch for clot lysis
44
Q

euglobulin clot lysis reference range

A

> 1 hour (usually less than 4 hours)
- increased fibrinolytic activity = clot lysis in <1 hour

45
Q

describe activated clotting time (ACT)

A
  • whole blood clotting time
  • point of care assay
  • monitors high dosage heparin during surgery
  • intrinsic pathway through contact factors

hemostasis (10 decks)

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