Section 8 Hemostasis testing Flashcards
Specimen collection
3.2% sodium citrate (light blue top tube)
EDTA - degrades Factor V
Heparin - inhibits coag factors
Binds Ca
Specimen adjustment
More Hct - less anticoagulant
Less Hct - More anticoag
Sample centrifugation
Coag uses PPP
Platelet uses PRP
Specimen handling
Always in plastic - glass has activating factors
for PT - RT for up to 24 hours
for APTT - up to 4 hours
Mechanical Coag instrumentation
Electromechanical: two probes. Circuit connected with clot formation
Magnetically: Detects movement change in small steel ball
Photoptical coag instruments
Turbometric: decrease in detection of light as clot forms
Nephelometric: Antigen-antibody complexes precip causing turbidity that scatters light. measures scattered like at 90 and 180 degree angles.
Trouble with turbidity of the sample
Prothrombin Time
Extrinsic Pthwy
VII
uses PPP
Reagent: thromboplastin
Does NOT test for factor XIII
Thromboplastin
Reagent in PT
Includes TF3
Phospholipid *PF3 replacement
CaCL to overcome the sodium citrate
PT reference range
11-13 seconds
International Normalized Ratio
PIVKA - proteins made by Vit K absence of antogonists
Reagent sensitivity to PIVKAs determines INR
International sensitivity index
ISI- baseline 1, further from 1 the reagent for PT is the more sensitive it is to PIVKAs
INR calculation
INR = (Patient PT/Normal PT)^ISI
RR: .9-1.2
Activated Partial Thromboplastin Time
Intrinsic Pathway
VIII, IX, X, XI, XII, PK, HMWK
Uses PPP
2 reagents: Activator and CaCL
RR: 26-36 seconds
APTT reagents
IX,XI, PK, HMWK
Contact activators
Phospholipids
APTT use
Monitors effects of Heparin
PT use
Monitors oral anticoag effects
Approach to bleeding disorders
PT normal/APTT prolonged: XII,XI,IX,VIII,PK,HMWK
PT prolonged/APTT normal: VII
PT & APTT Prolonged: X, V, II, I
Assuming a single factor defficiency
Thrombin Time
Tests for adequacy of fibrinogen
I -> Ia
Reagent: dilute Thrombin
RR: 14-20 seconds
50:50 mix
Determines if prolonged PT/APTT/TT is due to a factor deficiency or an inhibitor
50:50 mix results
Addition of normal plasma corrects towards the RR: factor deficiency
Addition of normal plasma has no effect: inhibitor
Fibrinogen assays
Immunological: Measures AG (total fibrinogen, even dysfunctional)
Fibrinogen activity: most common. Measures functional Fibrinogen
Fibrinogen assay vs TT
Fibrinogen uses 1:10 diluted plasma. minimizes inhibitors
reported as a standard curve vice a time in seconds.
Fibrinogen reagents
Calibrating reference
thrombin
Owrens veronal buffer
D-Dimers
formed in the process of 2nd degree fibrinolysis
Assays use monoclonal Abs, most commonly in latex agglutination
D-Dimer assay interpretation
D-Dimers present in fibrinolysis -> active thrombosis (DIC, DVT, PE)
Watch out for post zone phenomenon
RVVT
Russell Viper Venom Time
Activator of factor X. Ca and patient PPP tests common pthwy
RR: 20-30 seconds
Reptilase Time
RT
Acts same as thrombin on Fibrogen, excepts only cleaves A
Not inhibited by common inhibitors (heparin/anticoags)
FDP will inhibit but to a lesser degree
RT use
Differentiates lack of Fibrinogen from presence of inhibitor
RR: 16-22 seconds
TT is prolonged/RT normal
Heparin inhibitor
TT is prolong and RT is prolong
Inhibited by FDPs
Lack of fibrinogen
Urea solubility
Determines adequacy of Factor XIII
RR: 60-150%
