Establishing a reference range for thromboelastography maximum amplitude in patients administrating with antiplatelet drugs

Abstract Objective We aimed to establish the reference range of thromboelastograph (TEG) maximum amplitude (MA) in patients taking antiplatelet drugs. Methods Between August 2015 and July 2018, a total of 4614 patients administrating with antiplatelet drugs (clopidogrel and aspirin) were retrospectively analyzed in this study. For MAA parameter, we used the 10th and 90th percentiles to establish a reference range. The Spearman correlation was used for the correlation analysis among the inhibition rate of adenosine diphosphate (ADP%) and MAADP, inhibition rate of arachidonic acid (AA%) and MAAA. Then, through receiver operating characteristic (ROC) curve analysis of the best cutoff point, the reference ranges of MAADP and MAAA could be deduced. Consistency evaluation was performed by statistical analysis of ADP% and MAADP, AA% and MAAA pairing for 4459 patients. Results The reference range of MAA was 8.1‐25.8 mm. The reference range of MAADP was 19.8‐43.2 mm, and the corresponding sensitivity of two endpoints was 0.796, 0.856 and specificity were 0.897, 0.904, respectively. The reference range of MAAA was 18.9‐37.7 mm, and the corresponding sensitivity of two endpoints was 0.819, 0.829 and specificity were 0.922, 0.896, respectively. The inconsistency rate of ADP% and MAADP, and AA% and MAAA was 20.1% (898 cases) and 16.6% (738 cases), respectively. Conclusions The reference range of MAADP and MAAA established by us were better in sensitivity and specificity. MAADP and MAAA were more accurate than conventional inhibition rate analysis in guidance of antiplatelet therapy, especially in patients with excessive low MA or high MAA.


| INTRODUC TI ON
Thrombus is one of the most common lethal disease in non-malignant diseases, including myocardial infarction, cerebral infarction, pulmonary embolism, and so on. 1 Once onset, long-term anticoagulant therapy is needed. 2 For arterial thrombus, long-term treatment with antiplatelet agents is usually required, such as aspirin and clopidogrel. 3 It is necessary to monitor the blood coagulation functions of patients administrating with antiplatelet drugs to test the effectiveness of the drug.
Routine coagulation tests (such as activated partial thromboplastin time (APTT), prothrombin time (PT), and platelet count) are the most commonly used method for evaluating coagulation function.
These tests are often used as a starting place when investigating the cause of bleeding. However, routine tests possess only limited capacities to reveal patient's risk of bleeding and do not provide information on the risk for thrombus. 4 Besides, they do not provide specific data about clot quality or stability. 5,6 In comparison to the conventional tests, the thromboelastograph (TEG) hemostasis analyzer system can objectively reflect the blood clotting, fibrinogen/fibrin/platelet interactions, and the processes of formation, development, and dissolution of thrombus in the body. [7][8][9][10][11] TEG can reflect the function of platelet. 12,13 The therapeutic effect of antiplatelet drugs can be evaluated by adding ADP or AA inducer and deducting the coagulation effect of fibrin reticulum. Maximum amplitude (MA) parameters reflect the strength of blood clots. 14 The strength of the blood clot is composed of platelet aggregation, contraction, and fibrin network. 15 Platelets account for about 80%, and fibrin network accounts for about 20%. According to different inducers and detection types, MA can be divided into four types, including Kaolin activity (MA CK ), fibrin activity (MA A ), ADP-stimulated platelet activity (MA ADP ), and AA-stimulated platelet activity (MA AA ). 16,17 It is generally believed that drugs are more effective when platelet function is inhibited by more than 50%. 18 According to clinical experience and manufacturer's recommendation, our hospital has established a reference range of 40%-90% induction inhibition rate of ADP and 50%-90% induction inhibition rate of AA. However, the platelet inhibition rate needs to consider the MA CK value of the common detection and the MA A value of the fibrin network. When these two values are too high or too low, the calculated inhibition rate will be affected. Therefore, this study retrospectively analyzed the previous thromboelastograph (TEG) data, aiming to directly establish a reference range of MA A , MA ADP , and MA AA , and guide the rational use of drug in clinical practice.

| Patients
We retrospectively reviewed 4614 patients administrating with antiplatelet drugs (clopidogrel and aspirin), who were treated in

| TEG analysis
Platelet-fibrin clot strength measurements were carried out using the TEG Hemostasis System (Haemoscope Corporation). The TEG Hemostasis Analyzer with automated analytical software provides quantitative and qualitative measurements of the physical properties of a clot.
All analyses were performed with TEG disposable cups and pins as devised by the manufacturer and measurements were performed within 4 minutes of sampling. Briefly, a stationary pin is suspended into an oscillating cup that contains the whole blood sample. As the blood clots, it links the pin to the cup. Clot strength is determined by measuring the amplitude of the rotation of the pin, which increases proportionally with clot strength. Maximum amplitude represents maximum clot strength, expressed as the MA parameter.

| Statistical analysis
All statistical analyses were performed by using SPSS version 17.0 (SPSS Institute). The normality of distribution of continuous variables was tested by one-sample Kolmogorov-Smirnov test. Continuous variables with normal distribution were presented as means ± standard deviation (SD); non-normal variables were reported as median

| Demographic characteristics
We retrospectively reviewed 4614 patients administrating with clopidogrel and aspirin, who were treated in our department from

| Establishment and evaluation of MA A reference range
Considering the skewed distribution of MA A values ( Figure 1A), the reference range was 8.

| Establishment of MA ADP and MA AA reference range
The values of MA AA and MA ADP were skewed distributed

| D ISCUSS I ON
In recent years, the TEG has attracted much attention in assessing blood coagulation function and guiding blood transfusion in the preoperative period. Compared with routine coagulation function tests, TEG can reflect the first and second stages of hemostasis and fibrinolysis and can also reflect clinical bleeding more sensitively. 19 Besides, a significant negative correlation was also found between MA ADP and ADP%.
Since the reference range was negatively correlated with the inhibition rate, attention should be paid to clinical use. Exceeding the upper limit of the reference range indicated poor drug efficacy, and the closer the result was to the MA CK value, the worse the efficacy was. Below the limit of the reference range, the original inhibition  This study has several limitations. Firstly, this study was a retrospective, single-center and non-control study, which had certain limitations in clinical application. Secondly, this study only studied the MA parameters and did not analyze other TEG parameters such as r-time, k-time, and α-angle. 25 Therefore, multi-centered prospective studies should be conducted in the future to establish a more accurate reference range of TEG in patients taking antiplatelet drugs.
In conclusion, TEG could be used as a relatively reliable method for monitoring antiplatelet drugs. Compared with the traditional inhibition rate analysis, the direct establishment of MA A , MA ADP , and MA AA reference range could be more rationally in guide the use of drug in clinical practice.

ACK N OWLED G M ENT
None.