Transcript Coagulation Tests

General Approach in
Investigation of Haemostasis
Lecture 2: Bleeding Time
The process of haemostasis occurs in three
phases :
1. The vascular platelet phase, which assures primary
haemostasis
2. Activation of the coagulation cascade, which assures
formation of the clot
3. And activation of a series of control mechanisms, which
stop propagation of the clot and limit activation of the
coagulation cascade to the region of endothelial rupture.
Coagulation Tests
1. Tests of the Vascular Platelet Phase of Haemostasis:
 Bleeding Time (BT)
2. Tests of the Coagulation Cascade:
 Clotting Time ( CT) or Coagulation time
 Activated Partial Thromboplastin Time (APTT).
 Prothrombin Time (PT).
3. Tests of Fibrinolysis and the Mechanisms That
Control Hemostasis:
 Fibrin Degradation Products (FDP)
Bleeding Time (BT)
Principle:
 The bleeding time test is a useful tool to test for platelet
plug formation and capillary integrity. Occasionally, the
bleeding time test will be ordered on a patient scheduled
for surgery.
 The bleeding time is dependent upon
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The efficiency of tissue fluid in accelerating the
coagulation process
Capillary function and
The number of blood platelets present and their
ability to form a platelet plug.
Bleeding Time (BT)
 Prolonged bleeding times are generally found when
 The platelet count is below 50,000/µL
 When there is platelet dysfunction.
 Four procedures are currently in use for determining
the bleeding time:
 The Duke method.
 The Ivy Method.
 The Mielke Method.
 The Simplate or Surgicutt Method.
Duke Method
 With the Duke method, the patient is pricked
with a special needle or lancet, preferably on
the earlobe or fingertip, after having been
swabbed with alcohol.
 The prick is about 3–4 mm deep. The
technician then wipes the blood every 30
seconds with a filter paper.
 The test ceases when bleeding ceases.
 The usual time is about 1–3 minutes.
 No repeat testing is allowed due to space.
 The test causes nervousness in the patient.
 This test method is the easiest to perform, but
is the least standardized and has the less
precision and accuracy.
Ivy Method
 In the Ivy method, a blood pressure cuff is placed on the
upper arm and inflated to 40 mmHg to control capillary
tone and to improve the sensitivity and reproducibility– this
will maintain constant pressure within the capillaries and
help standardize the procedure- .
 A sterile, disposable blood lancet or scalpel blade is used
to make a shallow incision that is 1 millimeter deep on the
underside of the forearm.
 Every 30 seconds, filter paper is used to draw off the
blood.
 The time from when the incision is made until all bleeding
has stopped is measured.
Ivy Method
 The test is finished when bleeding has stopped
completely.
 A prolonged bleeding time may be a result from
decreased number of thrombocytes or impaired blood
vessels. However, it should also be noted that the depth
of the puncture or incision may be the source of error.
 Normal values fall between 2 – 7 minutes depending on
the method used.
 The greatest source of variation in this test is largely due
to difficulty in performing a standardized puncture. This
usually leads to erroneously low results.
Mielke Method
 A Modification of the Ivy Method.
 A Bard-Parker or similar disposable blade is used, along
with a rectangular polystyrene or plastic template that
contains a standardized slit. The blade is placed in a
special handle containing a gauge in order to standardize
the depth of the incision.
 The same procedure as described for the Surgicutt
method is employed.
Mielke Method
Mielke Method
 Advantages of this method include:
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That the surgical incision more closely approximates
the patient’s haemostatic response to surgery, when
compared to the puncture in the Ivy Method.
The depth of the incision can be controlled.
 Disadvantages of this method include:
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Patient anxiety, due to open blade.
Small scars might form.
Simplate / Surgicutt Method
 The Preferred Method
 Modified From the Ivy Method.
 The first bleeding time device introduced was the
Simplate.
 The Simplate device has a trigger and spring method
for the blade. The blade has a depth of 1.0 mm and a
width of 5.0 mm. Another brand name is the Surgicutt.
Simplate / Surgicutt Method
 Advantages of this method include:
 Instrument is a sterile, standardized, easy to use
device that makes a uniform incision.
 Instrument is a spring activated surgical steel blade
which is housed in a plastic unit. This eliminates
variability of blade incision.
 This method is the most standardized method of all the
bleeding time procedures.
 Disadvantages of this method include:
 Slight scarring can occur so patient should be
informed.
Materials:
 Blood pressure cuff
 Sterile, disposable blood lancet,
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capable of a puncture 5 mm wide and 1
mm deep
Stopwatch
Whatman No. 1 circular filter paper
Alcohol pads
Gloves
Butterfly bandage
Preparation of the Patient
 After proper greeting and identification of the patient,
explain the test for patient.
 It is critical that you ask the patient whether or not they
have taken aspirin, aspirin containing compounds (many
over the counter medications contain aspirin) or blood
thinners such as heparin or Coumadin recently. These
drugs will cause a falsely abnormal bleeding time and the
test should not be done.
Procedure:
1. Greet and identify the patient.
2. Explain the procedure to the patient.
3. Obtain a history about aspirin or aspirin containing compounds
taken within last 7 - 10 days.
4. Select a site on the patient's forearm approximately three fingers
widths below the bend in the elbow that is free of visible
subcutaneous veins.
5. Cleanse the outer surface of the patient's forearm by moving the
alcohol pad in concentric circles from the incision site outward;
allow to air dry.
6. Place a blood pressure cuff on the patient's arm above the elbow.
Turn the knob on the bulb of the sphygmomanometer until it stops.
Squeeze the bulb to inflate the sphygmomanometer. Inflate the
cuff and maintain pressure at 40 mm Hg.
Procedure:
Remove the Surgicutt device from the blister pack, being
careful not to contaminate or touch the blade-slot surface.
Remove the safety clip.
8. Holding the skin tight, depress the “trigger” on the bleeding
time device. The puncture must be performed within 30 to 60
seconds of inflation of the blood pressure cuff. Simultaneously
start the stopwatch.
9. After 30 seconds have passed blot (do not wipe) the blood with
the filter paper. The filter paper must not touch the wound on
the arm. Blot the site at regular thirty second intervals. Rotate
the filter paper after each 30 seconds.
10. When bleeding ceases and blood no longer is drawn to the
filter paper, stop the watch and release the blood pressure cuff
by turning the knob next to the bulb in the opposite direction
used to inflate the cuff. Remove the blood pressure cuff.
11. Record the bleeding time. Bleeding time is determined to the
nearest 30 seconds.
7.
Procedure:
12. If bleeding continues for more than 15 minutes, the procedure
should be discontinued, and pressure applied to the wound sites.
13. After ensuring that the bleeding has stopped, carefully bandage
the site.
14. Appropriately discard all used materials and wash hands.
Result
 Normal Values
 2.5 – 9.5 minutes
 The critical Value for bleeding time is > 15 min.
 If the puncture site is still bleeding after 15 minutes,
discountinue the test apply pressure to the site.
Document and report the results to the clinician.
Calibration , Quality Control:
 Calibration: None
 Quality Control:
No external QC is available. Care must be taken to
standardize the procedure.
The protocol must followed exactly!
Sources of Error
 If the patient has taken aspirin or aspirin-containing compounds 7 to
10 days prior to the procedure, the bleeding time may be
prolonged. The technician must determine the patient's history
concerning aspirin ingestion to ensure quality results.
About 20 different medications, including antihistamines and
nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen,
impair the platelets' ability to stick to wounds, and therefore produce a
longer bleeding time.
 Results may be affected by an improperly performed puncture. A
puncture that is too shallow, too deep, or in an inappropriate
location will adversely affect test results.
 The alcohol must be completely dried before making the puncture.
If residual alcohol is on a puncture site, the bleeding time will be
erroneously prolonged.
Sources of Error
 If the technician does not initiate timing of the procedure
simultaneously with the puncture, the results will be adversely
affected.
 If the technician allows the filter paper to touch the wound, the platelet
clot may be dislodged, causing falsely elevated results.
 If the stopwatch has not been appropriately calibrated, it may keep
incorrect time. Stopwatches should be calibrated on a regular basis
as a part of the quality assurance program.
 The direction of the incision should be consistent. A horizontal
incision gives a longer bleeding time than a vertical incision
 The bleeding time is prolonged in thrombocytopenia, hereditary and
acquired platelet dysfunctions, von Willebrand's disease, a
fibrinogenemia, severe hypofibrinogenemia, and some vascular
bleeding disorders
Sources of Error
 Errors producing false positive results
 Blood pressure cuff maintained too high (>40mm Hg (.
 Incision too deep, caused by excessive pressure on
the incision device .
 Disturbing the clot with the filter paper .
 Low fibrinogen (<100 mg/dl) or platelet count (100,00
/mm3(
 Drug ingestion affecting platelet function (e.g. Asprin (
 Errors producing false negative results
 Blood pressure cuff maintained too low (<40 mm Hg)
 Incision too shallow .