How to Do a PTT Test

Bleeding from small wounds should normally take two to five minutes to clot or coagulate. In some conditions, the clotting time may be extended due to various factors, including low-level or absence of clotting, use of medications like heparin which thins out the blood, inhibitors, or even high levels of clotting. To measure the time taken by your blood to clot when exposed to air, the Partial Thromboplastin Time test, or PTT, is conducted.

Things You'll Need

• Elastic band
• Syringe
• Alcohol
• Tube or air tight container
• Gauze pad / cotton ball
• Bandage
• Oxalate or citrate ions
• Centrifugation cell
• Flat dish
• Thromboplastin
• Warm water bath
• Thermometer
• Calcium chloride
• Timer

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Instructions

• 1

  Wrap the elastic band tightly on your upper arm to restrict blood flow and locate the veins. Wipe the syringe with alcohol dipped cotton to sterilize it. Locate veins and pierce the needle into the vein. Add oxalate or citrate ions to the tube. Attach the tube to the syringe and draw blood into it. Collect sufficient blood (not more than 20 ccs) and remove the needle. Release the elastic band and place a sterilized cotton ball or gauze pad on the needle prick. Hold with mild pressure. Seal the wound with a bandage.

• 2

  Place the blood into the centrifugation cell and switch it on. The blood will be separated into three main components. The first level will be plasma, the second will be white blood corpuscles, and the third level will be red blood corpuscles. Switch off the centrifugation when the separation is completed. Remove the plasma content only from the centrifugation cell into the flat dish.

• 3

  Add the thromboplastin to the plasma content. This will convert the prothrombin into thrombin.

• 4

  Heat the water in the water bath to 37 degrees C. Check for the right temperature with the thermometer. Keep the plasma mixture in the warm water bath for about two minutes and remove.

• 5

  Add calcium chloride to the plasma mixture and start the stop watch. The calcium chloride will counteract the sodium citrate that was earlier added to the blood when being drawn. The process of coagulation or clotting will start. Watch how much time the blood takes to clot and stop the stop watch when the blood has coagulated fully. Note the time taken--this will be the Prothrombin Time (PT).