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Coagulation Lab Tests


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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
other drugs that inhibit plt fctn
Conditions assoc with increased BT
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
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
Reliable, cost-effective
-easier than plt aggregometry
Principle of Platelet Aggregation
-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?
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
-mainly monitor oral anticoag therapy
-screen for inherited EXTRINSIC or COMMON pathway deficiencies
-acquired factor deficiencies
Principle of PT Test
-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?
~10-14 sec
varies from lab to lab because of different techs, reagents, populations, equipment...
Causes for elevated PT
oral anticoag therapy
vitamin K deficiency
Liver disease (acquired cond)
specific coag factor deficiencies
Purpose of APTT
-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
-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
- 30-40 sec
-varies lab to lab
APTT increased in...
INTRINSIC or COMMON pathway deficiencies
heparin therapy (main use)
What does elevated APTT w/ prolonged incubation mean?
Fletcher factor deficiency

-incubating 10 min instead of 4
Purpose & Principle of TT
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
Paraproteins (e.g., cryoglobulin)
Presence of heparin
Presence of FDPs
Presence of plasmin
Principle of Quantitative Fibrinogen
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
<200 in children normal!
-hypofibrinogenemia, dysfibrinogenemia
-liver disease
Causes of HIGH fibrinogen levels
Remember: Fibrinogen=Acute Phase Reactant
-estrogen therapy
Purpose of FXIII screening test
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
-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
-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
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?
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
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?
Chronic illness
FVIII and FIX deficiencies
congenital coag deficiencies
postpartum women

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