Classification of blood clotting tests
Substantially all coagulometers used in laboratory diagnostics are based on the methods of testing of the hemostasis system created more than fifty years ago. The majority of these methods are good to detect defects in one of the hemostasis components, without diagnosing other possible defects. Another problem of the actual hemostasis system diagnostics is the thrombosis prediction, i.e. sensitivity to the patient’s prethrombotic state.
All the diversity of clinical tests of the blood coagulation system can be divided into 2 groups: global (integral, general) tests, and «local» (specific) tests.
Global tests characterize the results of work of the whole clotting cascade. They suit to diagnose the general state of the blood coagulation system and the intensity of pathologies, and to simultaneously record all attendant influences. Global methods play the key role at the first stage of diagnostics: they provide an integral picture of alterations within the coagulation system and allow predicting a tendency to hyper- or hypo-coagulation in general.
Local tests characterize the results of work of the separate components of the blood coagulation system cascade, as well as of the separate coagulation factors. They are essential for the possibility to specify the pathology localization within the accuracy of coagulation factor.
A D-dimer (product of thrombi degradation) test can be specified separately. The rise of D-dimers concentration in the patient’s blood states the possibility of the completed thrombosis. To obtain a complete picture of the work of hemostasis by a patient, the doctor should have a possibility to choose which test is necessary.
According to the type of the investigated object, the following complementary groups of methods can be specified:
Tests in platelet poor plasma or in platelet free plasma (convenient for transportation; can be frozen; possibility to use optical observation methods; but the thrombocyte component of the hemostasis is not taken into account),
Tests in platelet rich plasma (close to real conditions in the body, but restrictions as to the terms of work),
Tests in whole blood (the most adjusted to human physiology; the test can be started immediately; but the least convenient due to terms of blood storage and difficulties of the results’ interpretation).
Specific global tests
investigation of the whole blood
no information about the thrombin formation kinetics, low separability of plasma and thrombocyte hemostasis contribution
Thrombin generation test (thrombin potential, endogenous thrombin potential)
possibility to use platelet poor plasma or platelet rich plasma
information about the catalyst of the main reaction – transformation of fibrinogen into fibrin
homogenous (activation in the whole sample volume)
non-homogenous: realization of the three-dimensional model of the clot growth
use of platelet free plasma
record of information about the clot formation as a diagram, giving the possibility to calculate the key parameters of the blood coagulation system
new test, not widely accepted
Specific local tests
characteristics of the velocity of passage of the intrinsic coagulation pathway
poor plasma (the most convenient to work with, but no realization of the thrombocyte clotting mechanism)
contact activation pathway
Prothrombin time test (or prothrombin test, INR, PT) – velocity of passage of the extrinsic blood coagulation pathway
not sensitive to deficiency of intrinsic coagulation pathway factors
Highly specialized methods to reveal the alteration in concentration of separate factors.
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