coagulation in the lab Flashcards
APTT prolonged but normal PT
intrinsic pathway
factor deficiency
- VIII
- XI
- IX
- XII
prolonged PT but normal APTT
extrinsic pathway
factor deficiency most likely VII
- could also be X, V, I, II
both APTT and PT prolonged
- deficiencies of factor II, V, X and I
multiple factor deficiencies
TCT prolonged
- deficiency of fibrinogen
- thrombin inhibitor (heparin or dabigatran)
what factors are of concern if APTT is prolonged
VIII
IX
XI
XII
mechanism of APTT testing
- venous blood collected into citrate
- removes Ca2+ inhibiting clotting
- spin sample down to collect plasma
- add phospholipid and activator
- then add Ca2+ to overcome citrate
- measure length of time for clot to form
mixing studies
1: 1 with normal plasma + incubation
- e.g. patient sample + normal sample
if sample correct to normal = factor deficiency
if sample does not correct = inhibitor present
causes of prolonged APTT
lupus anticoagulant
heparin
dabigatran
describe lupus anticoagulant
- is the most common cause of prolonged APTT
- plasma antibodies interfere with phospholipid in APTT
- does not cause bleeding
describe heparin
- up-regulates antithrombin therefore works as an anticoagulant
- prolonged 1+1 corrects with protamine
describe dabigatran
- is a direct thrombin inhibitor
- prolonged 1+1 doesn’t correct with protamine
describe factor inhibitors
autoimmune antibodies against clotting factor
- usually VIII
associated with bleeding and bruising
describe the prothrombin time test
- adding tissue factor to stimulate extrinsic pathway
- accesses vitamin K dependent factors
e. g. VII, II, X
ratio = PT (patient) / PT (normal)
- should be 1
describe thrombin clotting time
- thrombin added to plasma: which converts fibrinogen to fibrin
- will be prolonged for heparin and dabigatran
- protamine to differentiate
other test to assess coagulation
- single factor assays
- whole blood clotting tests
- platelet function assay
- D-dimer (fragments of broken down fibrin)
