HESS'S TEST
This test measures the capillary resistance (vascular fragility) as well as any abnormality of platelet number or function. It is a non-specific test and may not always give positive results. It is performed on the patient.
Principle
Impeding venous return raises blood pressure in the capillaries, resulting in small breaches. Normally these are plugged by platelets. But if breaches are more due to increased vascular fragility or if platelets are either less in number or defective in function, then blood extravasates and petechiae appear in greater number.
Requirements
Sphygmomanometer
Procedure
Apply the sphygmomanometer sleeve to the arm, and blow up it to 80 mm Hg pressure. Maintain this pressure for 5 min. Inspect the volar surface of the forearm for appearance of petechiae over antecubital fossa. Count the number of petechiae in a 3 cm2 area. On the off chance that there are at least 20 petechiae the Hess' test is positive.
Causes of positive Hess’s test
• Thrombocytopenia
• Platelet function defect
• Decrease in capillary resistance
BLEEDING TIME (BT)
Principle
When a standard incision is made on the volar surface of the forearm all mechanisms involved in arrest of bleeding are activated and after some time flow of blood stops. The time taken for the blood to stop flowing, without assistance, from the wound is known as the bleeding time. Bleeding time depends upon the number and function of platelets. On the off chance that the quantity of the platelets is diminished under a basic level or
these are practically unusual, the draining time is delayed. Bleeding time is also prolonged in von Willebrand disease in which, platelet function is disturbed due to absence of vWF.
Requirements
• Sphygmomanometer
• Lancet or template
• Circular filter paper
• Stopwatch
Method
There are two strategies by which the draining time can be estimated:
1. Duke's method. This method is some times used in infants and children.
2. Ivy's method. This is the standard method used.
Duke's method
In this method incisions are made in the ear lobe, pulp of the finger or heel (while it is warm), as these are the sites rich in capillaries.
• Clean the site with a soul swab.
• Allow the area to dry.
• With the help of a lancet, puncture deeply so that blood flows out freely. Start the stopwatch. At half min intervals blot the drop of the blood at the site of puncture with the help of a filter paper.
• Keep on doing so until blood stops coming out and there is no mark of blood left on the filter paper. As of now stop the stopwatch and note the time. This is the bleeding time.
Ivy’s Method
This is the standard method.
• Apply the cuff of the sphygmomanometer to the arm of the patient lying supine on a couch.
• Inflate the cuff to 40 mm Hg. This pressure should be maintained throughout the test.
• Clean the volar surface of the forearm with spirit swabs and choose an area of the skin that does not have any visible veins.
• Make two 4-8 mm long, 1 mm deep, separate punctures along the long axis of the forearm, 5-10 cm apart with standard depth lancet or by a template.
• Let the blood flow out freely and start stopwatch.
• Keep on blotting the oozing blood by gently touching it with edge of circular filter paper at 15 seconds intervals, until the blood stops coming out and no blood spot is left on filter paper.
• Stop the stopwatch and note the time. This is the bleeding time.
• If the bleeding time is more than 15 min and blood is still oozing, stop the test and apply pressure till bleeding is arrested. Write the result as bleeding time more than 15 min.
Precautions
• Check the platelet count before the test. If the count is less than 50x109/L then test should not be performed.
• There is dependably a propensity for the injury to close. Therefore, 1 mm deep incision should be made. A superficial incision will result in erroneous results.
• Blood pressure, number and size of incisions must be standardised.
• Area of skin selected for puncture should be clear of visible veins.
Reference range
Dukes' method: 2 - 7 min
Ivy's method (lancet): 2 - 7 min
Ivy's method (template): 2.5 – 9.5 min
Interpretation
WHOLE BLOOD CLOTTING TIME
Principle
At the point when blood got by a clean venepuncture is placed in a glass tube, thickening systems are enacted and soon a coagulation is framed. The time taken by the blood to clump in this manner is called entire blood thickening time (CT). Entire blood thickening time is an obtuse and vague test. It will be prolonged only in severe haemophilia or Christmas disease, when the factor levels are as low as 1 percent. It is sometimes used as a bedside procedure to screen for heparin effect and circulating anticoagulants. The Lee and White strategy is generally utilized.
Requirements
• Disposable plastic syringe
• Water bath at 37°C
• Stop watches (3)
Procedure
1. Place three glass test tubes in water bath at 37°C to warm.
2. Clean the venepuncture site with a spirit swab and let it dry.
3. Utilizing an expendable plastic needle gather 3 ml of blood. As the blood enters the syringe, start all the three stopwatches.
4. Put 01 ml of the blood in each of the three glass tubes already placed in the water bath.
5. At first slant the cylinders after 4 min and afterward after like clockwork to see regardless of whether the blood has coagulated.
6. When the blood clots in a tube, stop the stopwatch for that tube. Note the time taken by blood to clot for each tube. Take mean of the three readings as result. This is the clotting time.
Precautions
• The venepuncture ought to be perfect and just those examples are to be managed, which are gotten after a solitary prick. This is on the grounds that by rehashed injury more tissue factor is delivered and the coagulating time might be abbreviated.
• It is important to start the stopwatch as soon as the blood enters the syringe.
• The tubes should be of specified bore (10 mm) otherwise the result may vary.
Reference range
5-11 min
Interpretation
Clotting time is prolonged in:
• Severe Haemophilia.
• Severe Christmas disease
• Anticoagulant therapy particularly with heparin
• Factor XII deficiency.
• Circulating anticoagulants
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Good topic
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