Section 8: Hemostasis Testing Flashcards
If hct is low, do you need more or less anticoagulant?
- More anticoag
- Low hct means more plasma
If hct is high, do you need more or less anticoagulant?
- Less anticoag
- High hct means less plasma
What type of sample do coag studies vs platelet studies use?
- Coag studies use PPP
- Plt studies use PRP
Coag specimens should always be handled and prepared in what kind of material?
Plastic to prevent contact activation by glass
Prothrombin Time holding sample conditions
- room temp up to 24 hr
- FVII gets activated at colder temps
Plasma sample holding time conditions
- -20C for 2 wk
- -70C for longer than 2 wk
- freeze/thaw rapidly at 37C or ice crystals denature proteins
APTT holding sample conditions
- up to 4 hrs
- if on heparin centrifuged within 1 hr and tested within 4 hr
describe manual tilt tube method
- add reagents and specimens to tube and maintain heat by heat block
- time how long it takes for plasma to clot
when would you use manual tilt tube method?
- sometimes pt plasma won’t get turbid when it clots, and automated analyzers measure light transmittance change when a clot forms, so false neg
- so do manual method to troubleshoot
Electromechanical clot detection (mechanical)
- measures the change in conductivity between 2 metal probes immersed in plasma
- when fibrin clot forms it completes the previously unclosed circuit and stops the timer
Magnetically monitoring clot (mechanical)
- as clot forms, test solution increases in viscosity
- detects the change in movement of the steel ball by changing its range of motion or a break in contact with magnetic sensors
Instrument we’re using in coag lab
Diagnostica Stago STArt 4
Photo-optical (turbometric) coag testing
- measures change in OD of test sample
- light of a specific wavelength passes thru sample. As clot forms, the plasma becomes more opaque and decreases light detected
Nephelometric coag testing
- immunometric method form measuring proteins
- antigen-Ab complexes ppt -> turbidity-> scatters light
- detects variations in light scatter at 90° and 180°
- if immune complexes are too small then Ab are attached to latex particles
Chromogenic (amidolytic) coag instrumentation
- based on chromophore usually para-nitroaniline (pNA)
- goal is for coagulation protein (protease) to attack chromogenic substrate to free pNA
- free pNA is yellow. Color intensity proportional to amount of protease activity
Immunologic endpoint coag testing
- based on antigen-Ab interactions
- microlatex particles coated with specific Ab to analyte
- Beam of monochromatic light passes thru suspension
- wavelength of light greater than diameter of individual particles, so only small amount of light absorbed
- When Ag-Ab complexes form, their bigger diameter allows more light absorption
PT tests for what pathway? List factors
- Extrinsic
- FVII, X, V, II, I
Sample and reagents for PT?
- sample is PPP in sodium citrate
- thromboplastin (mix of phospholipids + TF3 + CaCl2)
PT procedure
- warm thromboplastin to 37°C
- PPP warmed to 37°C separate tube
- add thromboplastin to pt specimen and observe for clot formation
- time recorded for clot formation is the PT
PT cannot test for what?
- TFIII, Ca2+, PF3
- XIII
PT reference range
11-13 sec
PT used for what? What should the PT be?
- monitoring effects of oral anticoags
- these pt should have PT of 20-27 s
international normalized ratio (INR)
- standardizes pt results between labs
- commercial reagents are assigned a sensitivity index by WHO - thromboplastin is assigned value of 1
- Farther ISI from 1, the less sensitive it is to PIVKAs
PIVKAs
proteins induced by Vit K absence or antagonists
INR calculation
INR = (Pt PT/Normal PT)^ISI
INR ref range
0.9-1.2
APTT tests for what pathway? List coag factors
- intrinsic
- XII, XI, IX, VIII, PK, HMWK
Contact factors
XI, XII, PK, HMWK