clotting screen Flashcards
what are the key parts of a coagulation screen
PT/INR
APTT
(bleeding time)
Fibrinogen
Thrombin time
normal PT?
Normal INR?
What do they indicate?
12-13 seconds
0.8-1.2
The prothrombin time (PT) is a measure of the time taken for blood to clot via the extrinsic pathway (a good way to remember is that you ‘Play Tennis OUTSIDE’ therefore PT is EXTRINSIC).
Since the only factor in the pathway is VII (which is rarely deficient in isolation), these tests are a measure of overall clotting factor synthesis or consumption.This test can be affected by liver disease, disseminated intravascular coagulation (DIC), vitamin K deficiency and warfarin levels.
They indicate WIDESPREAD COAGULOPATHY
normal APTT ?
what does it indicate?
35-45 seconds
The activated partial thromboplastin time (APTT) is a measure of the time taken for blood to clot via the intrinsic pathway (a good way to remember, following PT, is that you ‘Play Table Tennis INSIDE’ therefore PTT is INTRINSIC).
Like with PT, APTT time will be affected by overall clotting factor synthesis or consumption.
APTT, however, can indicate issues with factors VIII (and vWF), IX, and XI specifically.
The main conditions that could result in an abnormal APTT include:
Haemophilia A (VIII – X-linked recessive)
Haemophilia B (IX – X-linked recessive)
Haemophilia C (XI – autosomal recessive)
von Willebrands disease (as vWF pairs up with factor VIII)
Heparin (as affects factor 10a)
antiphospholipid and APTT
anti-phospholipid syndrome can cause a high APTT despite being a disorder that causes clots, due to it inactivating the phospholipid used in APTT.
what does heparin impact in coagualtion screen
APTT
what type of disorders impact bleeding time?
platelet specific disorders will increase the overall bleeding time
normal is 1-6 minutes for finger prick
von Willebrand’s disease (vWF deficiency – autosomal dominant)
Bernard-Soulier syndrome (GpIb deficiency)
Glanzmann thrombasthenia (GpIIb/IIIa deficiency)
TTP/ITP/HUS/DIC
Thrombocytopaenia
fibrinogen.
normal level?
high or low means?
The fibrinogen level reflects the blood’s clotting ability (low = increased bleeding risk; high = may increase clotting)
Low levels are due to: increased consumption (e.g. disseminated intravascular coagulation) or decreased production (e.g. liver disease, malnutrition)
Low fibrinogen is more common in predominantly fibrinolytic types of DIC (e.g., patients with acute promyelocytic leukemia or obstetric-related DIC).
Fibrinogen is an acute phase protein and high levels may be due to: inflammation, malignancy, trauma, or infection
Sepsis increases fibrinogen levels, so sepsis-induced DIC may have elevated or normal levels of fibrinogen. Falling fibrinogen may suggest ongoing DIC with consumption of fibrinogen.
