Hemostasis Assays Flashcards
how is blood kept from clotting during a coagulation screening test?
- remove calcium using citrate
general activating agents for tests of coagulation
- calcium
- phospholipid
routine coagulation tests
- prothrombin time (PT)
- activated partial thromboplastin time (aPTT)
- thrombin time (TT) or thrombin clotting time (TCT)
TCT tests for
- conversion of fibrinogen to fibrin
- using thrombin
activating agents for thrombin time
- we do not use activating agents
how to do a TT test
- citrated plasma
- add thrombin
- record the time until clot forms
what causes a prolonged TT
- low fibrinogen
- abnormal fibrinogen
- inhibitor of added thrombin
another name for low fibrinogen
- hypofibrinogenemia
another name for abnormal fibrinogen
- dysfibrinogenemia
ways to get abnormal fibrinogen
- inherited
- acquired
acquired abnormal fibrinogen from
- severe liver disease
ways to get inhibitor of added thrombin
- direct inhibitor
- indirect inhibitor
direct inhibitor example
- argatroban
- dabigatran
indirect inhibitor example
- heparin
how to do the prothrombin time
- citrated plasma
- add thromboplastin and calcium
- record the time until clot forms
thromboplastin provides which compounds
- tissue factor
- phospholipid
prothrombin time measures which part of the coagulation cascade
- extrinsic pathway
if TF/VIIa can also activate factor 9, how come the PT is not sensitive to factor8/9 deficiency?
- the TF in vast excess drives the pathway toward X activation only
what causes a prolonged PT
- anything that prolongs the TT
- anything that lowers levels or inhibits common pathway factors
- low levels of Factor 7
sensitivity of PT compared to TT
- PT much less sensitive than TT
what things is the PT much less sensitive to
- heparin
- abnormal fibrinogen
- FDPs
the common pathway factors
- 10
- 5
- 2 (prothrombin)
- fibrinogen
how do we get low levels of factor 7?
- congenital
- acquired
acquired ways to get low levels of factor 7
- deficiency of vitamin K
- vitamin K inhibitors
- DIC
- liver disease
vitamin K dependent factors
- 2
- 7
- 9
- 10
- protein C
- protein S
how do vitamin K factors get into the plasma membrane
- inserted via their gamma carboxyl groups
purpose of vitamin K
- source of the gamma carboxyl group
sources of vitamin K
- diet
- gut flora
diet sources of vitamin K
- green leafy vegetables
causes of vitamin K deficiency
- dietary
- antibiotics
- fat malabsorption
- being a newborn
how to calculate the INR
mean normal PT
ISI
- given on the box for a new batch of thromboplastin
normal value for INR
- 1
aPTT measures which part of the coagulation pathway?
- the intrinsic pathway
how to perform the aPTT
- add activator
- add partial thromboplastin and calcium
- record the time until clot forms
what does the activator in the aPTT do?
- provides negative charges to activate the contact system
components of the contact system
- HMWK
- PK
- factor 12
what is missing in partial thromboplastin that is in complete thromboplastin
- tissue factor is missing
does partial thromboplastin have phospholipid
- yes!
what causes a prolonged aPTT?
- problems with common pathway factors
- problems with contact factors
- problems with hemophilia factors
- warfarin in excess
- severe vitamin K deficiency
- unfractionated heparan
- lupus inhibitor
CCHLWKH
Could Coagulation Have Less
Work? Hello, K!
factors in the common pathway affecting prolonged aPTT
- factor 2
- factor 5
- factor 10
- fibrinogen
contact factors affecting prolonged PTT
- factor 12
- HMWK
- PK
hemophilia factors affecting prolonged PTT
- factor 11 - hemo C
- factor 9 - hemo B
- factor 8 - hemo A
warfarin in excess or severe vitamin K deficiency due to their effects on
- 9
- 10
- 2
another name for lupus inhibitor
- lupus anticoagulant
what is a lupus inhibitor
- an autoantibody directed against phospholipid
how to tell if it’s a lupus inhibitor
- antibody prolongs coagulation reactions in test tube
- prolongation blocked by additional of more phospholipid in the reaction mix
broad differential of prolonged aPTT
- factor deficiency
- inhibitor
how a mixing study works
- take patient’s plasma
- mix it 1:1 with normal plasma
- repeat aPTT
if the clotting times remain prolonged, the result of the prolonged PTT is the
- inhibitor
if the clotting times normalize, the result of the prolonged PTT is the
- factor deficiency
- must be within normal range. cannot decrease and call it good
Ddx if both PT and PTT are prolonged
- deficiency of common pathway factor
- excess of warfarin
- excess of heparin
- multiple factor deficiencies
CWH MF
come hang with me, fucker!
multiple factor deficiencies due to
- severe liver disease
- severe DIC
tests of primary hemostasis
- bleeding time
- PFA 100
how PFA 100 works
- whole blood sucked through
- platelets plug up collagen coated grid
closure time in PFA 100
- how long it takes for flow to stop
what makes PFA-100 prolonged
- low platelet count
- low hemoglobin
- low vWF
- abnormal platelet function
low platelet numbers
< 100 x 10^9
low hemoglobin numbers
< 10 g/dL
