Coagulation screens Flashcards
why are coagulation screens carried out?
to monitor coagulation
what is prothombin time (PT)?
Measure of the time taken for blood to clot via theextrinsicpathway
’PlayTennisOUTSIDE = PT extrinsic’
What is added to plasma sample to measure PT?
Tissue factor is added to a sample of plasma along with calcium
Time until fibrin formation is measured
Normal range of prothombrin time?
12-13 seconds
Limitations to prothrombin time?
samples only useful less than 24 hrs old - otherwise unreliable results
What 4 conditions can prolong prothrombin time?
- chronic Liver disease
- Disseminated intravascular coagulation (DIC)
- Vit K deficiency
- Warfarin levels
What are the factors measured in the sample for prothrombin time?
FVII
FV, FX, prothrombin, fibrinogen
What are the activators of common pathway to measure prothrombin time?
Tissue factor
Calcium
Which pathways are assessed in prothrombin time measurements?
extrinsic and common
What is Activated Partial Thromboplastin Time (APTT)?
Measure of the time taken for blood to clot via the intrinsic pathway
’Play Table Tennis INSIDE = APTT intrinsic’
Normal range of APTT?
24 - 38 seconds
Limitations to APTT measurements?
Artefacts in sample
Insensitivity to clinically important bleeding disorders that have normal PT + APTT (mild vM diesase)
- Detects conditions not associated with bleeding
- eg. Lupus anticoagulant
Name 4 conditions that can have an abnormal APTT?
- Lupus anticoagulant
- Haemophilia A
- Haemophilia B
- DIC
- von Willebrands disease
What factors are measured in APTT?
FVIII, FIX, FXI, FXII
FV, FX, prothrombin, fibrinogen
what is the activator to measure APTT?
‘Contact activator’
Phospholipid + calcium
What pathways is being measured in APTT?
Intrinsic and Common
What is thrombin time measurements?
A measure of how long the blood’s plasma takes to form a clot
Normal range of thrombin time?
14 to 16 secs
Limitations of thrombin time measurements?
sample > 8 hrs = inaccurate results
What one factor often affects thrombin time measurements?
Low fibrinogen states
What is being measured in thrombin time?
Fibrinogen
What is the activator to measure thrombin time?
thrombin
what pathway is measured in thrombin time?
Fibrinogen → fibrin
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