Coagulation Lab Tests
Terms
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- Purpose of Bleeding Time
- Screen for defects of PRIMARY hemostasis. Measures in vivo plt function
- Normal range for BT
- 1-9 Minutes
- Causes of FALSELY increased BT
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aspirin
other drugs that inhibit plt fctn - Conditions assoc with increased BT
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Thrombocytopenia, Platelet dysfunction, vascular abnormalities, vWF disease, Bernard-Soulier,
Glanzmann's thrombasthenia, Congenital storage pool disease, Afibrinogenemia, Ehlers-Danlos syndrome, Uremia - Principle of Platelet Function Analysis
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Test cartriges w/ membranes coated w/ platelet agonists
-whole blood aspirated under controlled flow cond thru an aperture in membrane
-Plts undergo AAA on membrane surrounding aperture
-time req for plt plug to occulude aperture indicates plt function - Purpose of Platelet Function Analysis
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Reliable, cost-effective
-easier than plt aggregometry - Principle of Platelet Aggregation
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-PRP measured photometrically
-aggreg agent added, plts clump, % transmittance directly prop to amt clumping in plts
-Aggreg. agents: ADP, collagen, ristocetin, epinep., arachidonic acid - What are the primary and secondary waves in the platelet aggregation test?
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1=direct response of plts to aggregating reagent (shape change)
2=complete aggregation (endogenous ADP release from plt dense bodies) - What's special about using ristocetin in platelet aggregometry?
- it's action is dependent on interaction of vWF & GPIb/IX. Represents plt agglutination, not aggregation
- Purpose of PT Test
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-mainly monitor oral anticoag therapy
-screen for inherited EXTRINSIC or COMMON pathway deficiencies
-acquired factor deficiencies - Principle of PT Test
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-Plasma re-Ca in presence of excess tissue factor & time for clot formation is measured
-Test bypasses intrinsic factors
-unaffected by plts (because FIII has phospholipids) - What is the normal range for PT test? and what caveat is there?
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~10-14 sec
varies from lab to lab because of different techs, reagents, populations, equipment... - Causes for elevated PT
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oral anticoag therapy
vitamin K deficiency
Liver disease (acquired cond)
specific coag factor deficiencies
inhibitor - Purpose of APTT
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-screen to eval factors in INTRINSIC pathway (eval all xcpt VII,XIII,PF3)
-acquired or inherited
-monitor heparin therapy
-detect inhibitors in blood - Principle of APTT
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-Ca in blood bound by NaCitrate to prevent coag
-plasma after centrifg contains all intrinsic factors xcpt Ca & plts
-must add: Ca source (CaCl), Phospholipid substitute (PF3), activator (ellagic acid) - normal ranges for APTT
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- 30-40 sec
-varies lab to lab - APTT increased in...
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INTRINSIC or COMMON pathway deficiencies
heparin therapy (main use)
inhibitors - What does elevated APTT w/ prolonged incubation mean?
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Fletcher factor deficiency
-incubating 10 min instead of 4 - Purpose & Principle of TT
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measures conversion of fibrinogen to fibrin after adding excess thrombin to citrated plasma
-time for clot to form measured - Normal range for TT
- 10-15 sec
- Causes of prolonged TT
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Hypofibrinogenemia
Dysfibrinogenemia
Paraproteins (e.g., cryoglobulin)
Presence of heparin
Presence of FDPs
Presence of plasmin - Principle of Quantitative Fibrinogen
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ability of thrombin to convert fibrinogen to fibrn
-clotting time of diluted plasma INVERSELY prop to fibrinogen conc
-excess amts thrombin added to diluted plasma & clotting time noted - Normal range for Quant Fibrinogen
- 200-400 mg/dL
- Causes of LOW fibrinogen levels
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<200 in children normal!
-hypofibrinogenemia, dysfibrinogenemia
-liver disease
-DIC
-fibrinolysis - Causes of HIGH fibrinogen levels
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Remember: Fibrinogen=Acute Phase Reactant
-Pregnancy
-Trauma
-estrogen therapy - Purpose of FXIII screening test
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Remember: FXIII changes H-bonds to covalent in clot
-deficiency of FXIII results in unstable clots
-test is time for clot to dissolve in 5M urea. Normal=~24 hrs - Principle of FDP
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-latex particles coated w/ Ab to fibrinogen fragments D & E
-positive is agglutination - Purpose of soybean trypsin inhibitor in FDP
- prevents In vitro fibrinolysis
- Normal range for FDP
- 10-40 ug/dL
- Purpose of D-Dimer
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-latex agglut for specific cross-linked fibrin derivatives w/ D-Dimer domain
-eval pts w/ DVT or PE (which have elevated values) - Purpose of mixing studies
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differentiate a factor deficiency from the presence of an inhibitor.
Mix pt. plasma w/ normal plasma. If inhibitor, will also inhibit normal factors, thus no correction - What are 2 specific coagulating inhibitors, and what would the results be in mixing studies?
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Lupus-like anticoagulant,
Factor VIII inhibitor
-There will be NO CORRECTION after 2 hr incubation
(FVIII inhibitor corrects after immediate, but goes away) - What is the dRVVT
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Dilute Russell's Viper Venom Time
-has venom, Ca, LIMITED conc phospholipid
-venom in presence of FV, phospholipid, and Ca will activate FX => prothrmbn to thrombin
-dRVVT ELEVATED w/ lupus anticoagulant - What patients do we see inhibitors?
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Chronic illness
FVIII and FIX deficiencies
congenital coag deficiencies
postpartum women