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Activated clotting time (ABC)
Last reviewed: 04.07.2025
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ABC is normal - 80-120 s.
The method of determining the activated blood clotting time (ABC) allows to control and regulate the level of heparinization of the patient during the work of artificial organs (heart-lung machine, artificial kidney, liver, hemosorption), calculate the neutralizing dose of protamine sulfate and evaluate the completeness of heparin neutralization. A great advantage of the method is the ability to identify patients with varying degrees of resistance to heparin, when in order to achieve the optimal degree of heparinization it is necessary to administer heparin to the patient in a dose of up to 13 mg / kg, while 2-4 mg / kg is usually used. Practical use of the ABC method to control the level of heparinization is described on the example of its application in patients operated on artificial circulation. An individual graph is plotted for each patient. On the ordinate axis - the amount of heparin administered to the patient (mg / kg), on the parallel scale - the level of protamine sulfate (mg / kg), on the abscissa axis - the ABC value in seconds. The vertical lines delimit the optimal ABC limits during artificial circulation - 480-600 sec. Optimal heparinization of a patient undergoing surgery under artificial circulation is usually achieved with a heparin dose of 2-4 mg/kg and an ABC value of 480-600 sec. The amount of heparin (ml) to be administered to the patient is calculated as follows: 1 ml (1 ml contains 5000 U) of heparin solution contains 50 mg of pure heparin, if the patient's body weight is 80 kg, then the amount of heparin (ml) is equal to: 80 kg • 3 mg/kg (2-4 mg/kg) = 240 mg of pure heparin; 240 mg: 50 mg = 4.8 ml of heparin. The initial ABC value, which is determined for the patient before connecting the artificial circulation apparatus, is plotted on the graph.
Five minutes after the calculated dose of heparin has been administered, ABC is determined again and this point is marked on the graph - the intersection of the ABC value and the administered dose of heparin (mg/kg); points A and B are connected by a straight line, which is then used to monitor the level of heparinization during artificial circulation. If this ABC value is not within its optimal values (480-600 sec), i.e. there is refractoriness to heparin, the additional amount of heparin for administration is calculated using the method below. ABC is then determined every 30 minutes of artificial circulation.
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