LO5

What pathways and factors are measured by APTT

intrinsic and common pathways - XII, XI, IX, VIII, X, V, II, I, HMWK, Prekallikrein

Which factors aren’t tested for by APTT

Factor XIII and VII

What is APTT most sensitve to

VIII and IX deficiencies - Hemophilia - sever fibrinogen deficiencies

What does prolonged APTT mean

factor deficiency

WHat is the purpose of ordering an APTT

monitoring heparin therapy - test of choice to screen factor deficience of intrinsic and common - detects phospholipid inhibitors

What is the specimen collected for APTT

NaCitrate - Platelet poor plasma

WHat is in the reagent for APTT

partial thromboplastin and CaCL2

What is within the Controls of APTT

commercial - lyophilized or frozen - normal and abnormal

What is partial thromboplastin within the reagent

composed of phospholipid (platelet of source or substitute) and activator

WHat does an activator do in the partail thromboplastin reagent

maximum activation of the contact factors is accomplished and speeds up the reaction

What is the CaCl2 in the reagent

supplies Ca for the cascade - sodium citrate binds to calcium to prevent coagulation - we need to supply it for coagulation to occur

WHat is the procedure of APTT

PPD is added to citrate - APTT reagent is added and mixture is incubated at 37 degrees - after incubation period, add warmed calcium chloride and start timer - when clot is detected, timer is stopped

WHat is the APTT reference range? What is the critical range?

25-40 seconds - Critical >150 seconds

What causes prolonged APTT

Factor Deficiency - acquired antibody to a specific factor - aquired inhibitor (inhibio=tor to phospholipid - severe liver disease - heparin therapy

What is the criteria for a factor to be deficient

factor is less than 50% of normal

What causes a shortened APTT

high levels of Factor VII - acute phase reactant

What are the most common single factor deficiences

VIII - Hemophilia A, IX - Hemophilia B, XI - Hemophilia C

What is heparin

produced naturally in body in mast cells and basophils - commercial preparations are glycosaminoglycans with molecular weights - effect of heparin depends on the patients amount of antithrombin

What is antithrombin

coagulation inhibitor - main target of inhibitation are IIa and Xa (forms complex with them and inhibits their action) - Also inhibits IXa, XIa, XIIa, plasmin, and kallikrein - does not inhibit VIIa

What is the relationship between heparin and AT

AT is heparin’s cofactor - heparin accelerates AT action, heparin prevents clot from forming

what happens when there is no heparin

AT neutralizes thrombin and Xa forming 1:1 complex in several minutes

What does therapeutic heparin do

same thing as natural heparin

WHat is high molecular wight heparin (unfractionated heparin

most common heparin treatment - has a short half life so requires frequent administration - IV - enhances AT activit against thrombin and Xa

What is unfractionated heparin used in preventionand treatment of:

venous thromboembolism, unstable angina, during and after coronary angioplasty, during cardiovascular surgery

What are therapeutic levels -

1.5-2x the patients - results vary depending on reagent - standardization of results has not yet been achieved

How does the admnistration of heparin work

small amounts of heparin are given until therapeutic levels have been reached - monitored every 6-24 hours - levels should be reached within 24 hours

WHat does long term heparin therapy do

decrease AT which can be dangerous - switch to different anticoagulant once stabilized on heparin

What is Heparin Induced Thrombocytopenia

IgG antibodies cause platelet consumption by the spleen = decrease PLT - may also affect formation of thrombi = life threatening = we must monitor platelet counts as heparin induced thrombocytopenia may occur

What should be monitored on HIT

APTT and Platelets - if platelets drop below 50% of baseline, stop heparin