Activated partial thromboplastin time
Reference values of APTT are 25-35 s.
APTTV is one of the most valuable common tests to get an idea of the blood coagulation system. APTTV is a test that detects the clear plasma defects of the internal X-factor activation system in the first phase( the formation of prothrombinase) of blood coagulation excluding
. The extension of the ACTTV reflects the deficiency of plasma factors( except VII and XIII) and is observed with a significant decrease( below 25-10%) decrease [Barka-gan ZS, 1988].The prolongation of the APTT indicates a predominance of hypocoagulation.
Reasons for prolonging the
APTT ■ Violation of the APTT values in normal prothrombin and thrombin time is observed only in case of deficiency or inhibition of factors VIII, IX, XI, XII, as well as prekallikrein and high-molecular kininogen. Of these forms of pathology, deficiency and / or inhibition of factors VIII and IX are most often observed, which is characteristic of haemophilia A and B, as well as deficiency of von Willebrand factor. More rarely in the blood of previously healthy individuals, there appear immune factor VIII inhibitors.
■ Deceleration of coagulation in determining both APTT and prothrombin time in normal thrombin time and fibrinogen concentration is observed with deficiency of factors X, V, II, and also when exposed to indirect anticoagulants.
■ Prothrombin time prolongation with normal indications of APTT and thrombin time is characteristic only of factor VII deficiency.
■ Extension of APTT, prothrombin and thrombin time is observed with deep hypofibrinogenemia, treatment with fibro-rhinolysis activators. The prolongation of the clotting time only in the thrombin test is characteristic for dysfibrinogenemia and violations of the polymerization of fibrin monomers.
■ Afibrinogenemia and hypofibrinogenemia, both congenital and associated with severe liver damage, are accompanied by an extension of APTT.
■ In the course of heparin therapy, APTT, prothrombin and thrombin time are prolonged. Importance is attached to the definition of APTTV.It is known that patients may have increased and decreased sensitivity to heparin. Finally, the question of tolerance to heparin can be refined by re-determining the APTT for 1 h before the next administration of heparin. If APTTV at this time will be elongated more than 2.5 times compared with the norm, they detect increased sensitivity to heparin and reduce its dose or increase the interval between administrations.
■ Elongation of APTT can indicate the presence of a patient with a wave anticoagulant( BA), in the absence of violations of other coagulogram parameters.
In Table.data are given on the combinations in which indications of baseline coagulation tests are violated with the deficit of various coagulation factors and the action of anticoagulants. The shortening of APTT indicates a predominance of hypercoagulation and is noted in the first( hypercoagulable) phase of acute DIC syndrome.
Table Results of the main coagulation tests with deficiency of different coagulation factors
Table Results of the main coagulation tests in the presence of deficiency of various coagulation factors
Detection of signs of hypercoagulation( shortening the time of blood coagulation, prothrombin time, APTT) is considered an indication for medication of medium molecular weight( 15 000-25000 Yes) or low molecular weight( 4200-6100) heparin. To monitor the adequacy of ongoing therapy 2 times a day, it is necessary to determine the time of blood coagulation or APTT.When examining the time of blood clotting, infusion of heparin( using infusion pumps) should be selected in such a way as to maintain this index within 15-23 min, and APTT is 2-3 times higher than normal. Recommended regimens for monitoring the treatment of medium-molecular heparin are given in Table. In addition, when administering high doses of heparin, daily monitoring of the content of ATH is required, since its level is sharply reduced as a result of consumption.
Low molecular weight( fractionated) heparins cause less consumption of ATH, practically do not activate platelets and cause no immune reactions. They are not able to bind simultaneously thrombin and ATH, therefore, they do not accelerate the inactivation of ATH, but retain the ability to catalyze inhibition of Xa ATP factor. Acceleration of the inactivation of factor Xa does not require the formation of a ternary complex and can be achieved only through the binding of heparin with ATH( depending on the preparation of low molecular weight heparin, the anti-Xa / anti IIa ratio is 2: 1 to 4: 1).
To control the treatment with low molecular weight heparin, a more sensitive test is used than APTT-determine anti-Xa plasma activity( quantitative determination of heparin, where Xa is used as a reagent for
).In determining the anti-Xa activity of the plasma, dextran sulfate is used to drive out heparin from the complex with proteins, which provides an accurate measurement of the number of complexes Xa and ATH.As an indicator, the reaction with the chromogenic substrate on the factor Xa is used. The recommended regimens for monitoring the treatment of low-molecular heparin are given in the table.
Table Control scheme for treatment with medium molecular weight heparin
Table Control scheme for treatment with medium molecular weight heparin
Table Treatment regimen for low-molecular heparin
Table Treatment regimen for low-molecular-weight heparin
With MI on the effectiveness of anticoagulanttherapy( heparin) is judged by the degree of extension of APTT, which also reflects the patency of the coronary arteries. In Fig.the relationship between the degree of patency of the coronary arteries( according to angiography) and the duration of APTT in anticoagulant therapy with heparin in patients with MI( Alexander R. W. et al., 1998) is shown.