PREFINAL LABORATORY L2: CT/BT Flashcards
what does bleeding time evaluate
function of platelets, von Willebrand factor and small blood vessels
is bleeding time a screening or diagnostic test
screening test
bleeding time is directly affected by what factors
platelet count and platelet’s ability to form a plug
it is required for platelet adhesion to a vessel wound with exposed subendothelial collagen
von Willebrand factor
factors that may affect the result of bleeding time
1) deficiency in von Willebrand factor
2) thickness of bv
3) ability to constrict and retract of bv
T or F:
Coagulation process does not affect the bleeding time
T
(unless there is a presence of severe deficiency)
how can aspirin affect bleeding time
prolong bleeding time by helping not to have thrombus formation
bleeding time should not be performed after taking aspirin for how many days
7 days
bleeding time should not be performed after taking NSAIDs for how long
24 hours
two methods of bleeding time
Ivy method
Duke method
identify:
an incision on the volar surface of the arm is made
Ivy method
in Ivy method, the sphygmomanometer is used and inflated up to how many mmHg
40 mmHg
identify:
performed by making a puncture in the earlobe and the time required for the bleeding to stop is measured
Duke method
In Duke method, what is the depth of the puncture using a sterile lancet
2-3 mm
in Duke method, when is the stopwatch started
when the first drop of blood appears
how many seconds is the interval in Duke method
15 or 30 seconds
reference value of Ivy method
2-9 minutes
reference value of Duke method
1-3 minutes
in Ivy method, puncture must be made in an area that is free of
large superficial blood vessels
depth of puncture in Ivy method
3 mm
when is the sphygmomanometer removed in Ivy method
after the bleeding ceases
assesses platelet function by measuring how quickly a blood clot shrinks and draws the edges of a broken blood vessel together
clot retraction test
principle of clot retraction test
fresh whole clotted blood is placed in a 37C water bath and inspected at 1, 2, 4 and 24 hours for the presence of retracted clot
when is maximum clot retraction observed
24 hours, time the dot occupies about half the original blood volume
normally, when does clot retraction commences
within 30 seconds after the blood has clotted
there should be appreciable clot retraction at the end of how many hours
1 hour
most retraction occurs within how many hours
first 4 hours
clot retraction should be complete within how many hours
24 hours
abnormal clot retraction time is observed in what conditions
1) Glanzmann’s thrombasthenia
2) thrombocytopenia
3) paraproteinemia (e.g. multiple myeloma)
in what disease where there is a small clot formed with an increased amounts of red blood cells expressed from the clot
dysfibrinogenemia or hypofibrinogenemia
term used to describe a small clot formed with an increased amounts of RBC expressed from the clot
RBC fall out
what happens in paraproteinemia
there is interference of fibrin formation by abnormal proteins
what happens in DIC
the formed clot will appear small and ragged with increased RBC fall out
what is the degree of clot retraction in specimen with erythrocytosis
limited due to large volume of blood cells within the clot
what is the degree of clot retraction in specimen with anemic conditions
increased
manner of reporting of clot retraction
1) no retraction
2) partial retraction
3) complete retraction
4) very poor
5) poor
6) partial normal retraction
methods of clotting time
Slide method
Lee & White method
principle of clotting time
the coagulation time of whole blood is the length of time required for a measured volume of blood to clot under specific conditions
the lack of sensitivity and precision of the LW led researchers to look for better methods of monitoring what
heparin therapy
this was recognized to be sensitive to heparin
Partial Thromboplastin Time (PTT)
what year was PTT recognized
1964
who developed the activated clotting time test (ACT)
Dr. Paul Hattersley
how many mL of whole blood is used in ACT
2mL
tube used in ACT
gray stoppered BD vacutainer with diatomaceous earth (diatomite)
function of diatomaceous earth
functions as the activator of the contact factors
contact factors
1) factor XII (Hageman factor)
2) high-molecular weight kininogen
3) prekallikrein
ACT required blood to be constantly warmed at what temp
37C
when is the tube tilted in ACT
after the 1st minute
how many second intervals in ACT
5-10 until the clot forms
coagulation is normally complete for how long
less than 101 seconds
this is commonly known as clotting time
capillary blood method (slide method)
reference value of clotting time
2-4 minutes
what should be observed in clotting time before stopping the timer
fibrin thead
how many tubes are used in Lee and White
3 13x100 mm test tube
needle gauge used in LW method
20
amount of blood drawn in LW method
4 mL
how many mL of blood in each tube in LW
1 mL each, last 1mL is discarded
when is the timer started in LW method
after blood is placed in tube #3
when is the #1 tube tilted
5 minutes
angle of the tube should be tilted
45 degrees
the tube is titled every how many seconds
30 seconds until the blood is completely clotted
how many seconds before proceeding with test tube #2
30 seconds after tube #1 is clotted
what tube is the reported result
3
why is tube #3 the reported result
since agitation and handling speed up coagulation
reference value of LW method
5-15 minutes
