Measurement of functional fibrinogen levels using the Thrombelastograph.

STUDY OBJECTIVE: To validate a Thromboelastograph (Haemoscope Corporation, Niles, IL) assay for functional fibrinogen. DESIGN: Correlation study of the Thromboelastograph assay with two conventional fibrinogen assays by the standard Clauss method. SETTING: Research laboratory of a university medical center. PARTICIPANTS AND INTERVENTIONS: Blood samples were obtained from 19 healthy volunteers. MEASUREMENT AND MAIN RESULTS: Thromboelastograph assays, using heparinized whole blood from 19 healthy donors, indicated that reptilase-XIIIa mixture (Activatorf)-generated clot shear elasticity in dynes per square centimeter (Gf) correlated with fibrinogen (mg/dL). Blood from four donors was used to define the contribution of hematocrit (Hct) to Gf by titration with platelet-rich plasma. The Gf versus Hct gave linear correlations (r2 = 0.746) with Gf = 1258 - 17.8 x % Hct. A commercial collection of 19 normal, 10 borderline, and one deficient for functional fibrinogen-citrated plasmas was assayed for Gf after recalcification using Activatorf. Of the 30 plasma samples, four were from factor X- or factor VII-deficient donors and one was from a coumadin-treated donor. There was a linear correlation of Activatorf Gf with functional fibrinogen (r2 = 0.940) with Gf = -730 + 9.21 x fibrinogen (mg/dL). CONCLUSION: Thrombelastography with Activatorf may be used to determine fibrinogen levels in whole blood.

Measurement of patients' bivalirudin plasma levels by a thrombelastograph ecarin clotting time assay: a comparison to a standard activated clotting time.

Standard activated clotting time (ACT) tests have a poor correlation to bivalirudin levels, leading to uncertainty regarding adequate anticoagulation in percutaneous coronary intervention patients. We tested a Thrombelastograph (TEG) ecarin clotting time (ECT) assay for sensitivity to bivalirudin using blood from 80 patients undergoing interventional cardiology procedures with bivalirudin anticoagulation. This was compared to a standard Hemochron ACT assay using diatomaceous earth. With the TEG assay, the direct thrombin activator, ecarin, was used to initiate coagulation and measured as the reaction time. Plasma samples were evaluated for bivalirudin by a chromogenic assay at an independent hematological laboratory. Linear regression of the standard ACT versus bivalirudin level gave an r = 0.306 whereas the TEG ECT gave a much higher r2 = 0.746 (both P < 0.0001). The TEG ECT should prove more useful than the standard ACT for monitoring bivalirudin anticoagulation across the clinically therapeutic range.

Evaluation of a point-of-care coagulation analyzer on patients undergoing cardiopulmonary bypass surgery.

STUDY OBJECTIVE: To evaluate a point-of-care (POC) coagulation monitoring analyzer (CoaguChek Pro DM) in patients undergoing cardiopulmonary bypass (CPB). DESIGN: Prospective, blinded study. SETTING: University hospital. PARTICIPANTS: 32 patients scheduled for elective cardiac surgery with CPB. INTERVENTION: Arterial blood samples were drawn four times: preoperatively, postinduction, and 10 minutes and 60 minutes after reversal of heparin with protamine. MEASUREMENTS AND MAIN RESULTS: Activated partial thromboplastin time (aPTT) and prothrombin time (PT) were measured with a point-of-care system--CoaguChek Pro DM as well as with the Core Laboratory facility using a MD180 analyzer. A total of 128 consecutive paired analyses were conducted. There was very good agreement of the point-of-care-based monitoring of aPTT and PT with the Core Laboratory-based monitoring of aPTT and PT (positive correlations by linear regression analysis: r2 = 0.83 and 0.92, respectively). The turn-around time (time from blood sampling until availability of data for the anesthesiologists) was significantly shorter for the point-of-care system (averaging <10 min) than for the Core Laboratory system (averaging >30 min). CONCLUSION: CoaguChek Pro DM is a reliable and time-efficient point-of-care system for monitoring coagulation of patients undergoing CPB. The use of this system may improve patient care in this group through timely and accurate clinical decisions.

Correlation of perioperative platelet function and coagulation tests with bleeding after cardiopulmonary bypass surgery.

The authors evaluated the correlation of post-cardiopulmonary bypass surgery bleeding, measured as 24-hour chest tube output/kilogram body weight, with platelet function tests using glass bead adhesion and Thrombelastograph Platelet Mapping (Haemoscope Corporation, Niles, Ill); coagulation tests; patient characteristics; surgery parameters; and visual assessment of surgical field bleeding before closure as not bleeding (code 1), oozing (code 2), and excessive bleeding (code 3). All platelet function and coagulation tests indicated significant dysfunction 15 minutes after protamine neutralization of heparin. With the exception of glass bead adherence, these assays indicated poor recovery of function 1 hour postoperatively. By multiple regression, the most significant predictors of postoperative bleeding were a low body mass index (BMI) (P < 0.0001), lowest core body temperature (P = 0.0006), and cross clamp time (P < 0.0001). Low core temperature was significantly (P < 0.0001) correlated with cross clamp time, which the authors believe is the most likely cause of coagulation and platelet dysfunction. None of the platelet function tests significantly correlated with bleeding. Looking at the highest quartile of chest tube output patients (n = 19) versus the upper and lower 50th percentile of coagulation and platelet function, bleeding could be explained for 11 patients by BMI plus surgery parameters along with coagulation and/or platelet dysfunction. In three cases without negative surgery parameters, coagulation dysfunction was observed. The remaining five cases did not give a clear indication of which parameters were primarily responsible for the bleeding.

Comparison of modified Thrombelastograph and Plateletworks whole blood assays to optical platelet aggregation for monitoring reversal of clopidogrel inhibition in elective surgery patients.

Clinically monitoring recovery from clopidogrel and nonsteroidal anti-inflammatory drug (NSAID) inhibition requires whole blood assays corresponding to a standard methodology such as platelet-rich plasma aggregation monitored optically (OPA). We compared OPA, using an ED 50 dose of adenosine diphosphate activation, with 2 whole blood assays, Plateletworks (PWA) and modified Thrombelastograph (TEG). Two sets of assays were performed on 43 surgery patients while on clopidogrel and off clopidogrel to determine the reversal of absolute and relative inhibition. The modified TEG had Spearman correlations with OPA for absolute (rho = .424; P = .006) and relative inhibition (rho = .742; P < .0001). PWA correlations with OPA gave absolute (rho = .28; P = .08) and relative inhibition (rho = .46; P = .004) values. Bland-Altman analysis indicated agreement of both tests with OPA, showing constant biases of about 18% and some dependency on mean magnitude error. Cohen effect size thresholds defined nonresponders as < 7.7% clopidogrel inhibition relative to baseline recovery of full platelet function. Apparent nonresponse to clopidogrel or lack of platelet recovery did not correlate with statin or NSAID therapies. These PWA and modified TEG whole blood assays could prove useful for monitoring the reversal of clopidogrel and NSAID inhibition before surgery. More important, these assays done at baseline and after beginning clopidogrel therapy could monitor the effectiveness for the individual patients with cardiovascular disease and help identify the need for alternative therapies.

A Thrombelastograph whole blood assay for clinical monitoring of NSAID-insensitive transcellular platelet activation by arachidonic acid.

Optical platelet aggregation (OPA) with platelet-rich plasma (PRP) was compared with a Thrombelastograph (TEG) whole blood assay for monitoring arachidonic acid (AA)-induced platelet activation. Assays were performed on 47 interventional cardiology and 24 general surgery patients receiving aspirin therapy for cardiovascular disease, as well as 48 volunteers asked to take nonsteroidal anti-inflammatory drugs (NSAIDs) or 12 volunteers on chronic NSAID therapy unrelated to diagnosed cardiovascular disease. Whole blood TEG monitoring of NSAID inhibition detected NSAID-insensitive AA activation of platelets in a significantly higher number of cardiology (23%) and surgery (25%) patients and normal volunteers on chronic NSAID (25%) therapy relative to normal subjects not on chronic NSAID therapy (0%). Whole blood NSAID insensitivity was observed with cyclooxygenase-I inhibitors, such as aspirin and ibuprofen; was not affected by Celebrex, a cyclooxygenase-II inhibitor; but was completely inhibited by thromboxane-receptor antagonists. This was not due to platelet NSAID insensitivity, because complete inhibition of AA-activation responses in PRP was observed with either TEG or OPA assays. We confirmed that thromboxane B(2) formation in PRP from NSAID-insensitive subjects was completely inhibited by NSAIDs. However, significant amounts were formed in whole blood from NSAID-insensitive subjects, but not in whole blood from NSAID-sensitive subjects. Thromboxane formation after AA addition was not found in washed blood cells with 90% reduced platelet counts or in leukocyte-rich buffy coat fractions, but could be restored by addition of PRP. NSAID-insensitive activation was inhibited by nordihydroguaiaretic acid, with an IC(50) of 30 micromol, implicating 12- and/or 15-lipoxygenases in this transcellular pathway.

A novel modification of the Thrombelastograph assay, isolating platelet function, correlates with optical platelet aggregation.

Flow cytometry, singlet platelet counting, and optical aggregation have been used to monitor clopidogrel and glycoprotein IIb/IIIa (GPIIb/IIIa) platelet antagonists. Optical aggregation is considered the gold standard, but neither it nor flow cytometry is convenient in larger-scale clinical studies or point-of-care systems. Singlet platelet counting, a point-of-care assay correlated with optical platelet aggregation, only provides a measurement of platelet function at a single point in time. The Thrombelastograph is used to assay whole blood for thrombin-generated maximal clot-shear elasticity, referred to as the maximal amplitude (MA). Although platelet dysfunction, thrombocytopenia, and the in vitro effect of strong inhibitors such as IIb/IIIa antagonists can be observed, with thrombin generation milder platelet inhibitors cannot be assessed. We modified the Thromboelastograph assay, using reptilase and factor XIIIa, to form a clot, without thrombin generation, in heparinized whole blood. The resulting clot MA is dependent on added platelet agonists such as ADP or arachidonic acid, is sensitive to platelet antagonists, and provides a continuous measure of platelet function more analogous and better correlated with optical aggregation. This novel modification of the Thromboelastograph assay should prove to be a useful point-of-care whole-blood assay with which to monitor the effects of GPIIb/IIIa, ADP, and thromboxane A(2)-receptor-inhibiting drugs in patients.

A novel thrombelastograph tissue factor/kaolin assay of activated clotting times for monitoring heparin anticoagulation during cardiopulmonary bypass.

We used a thrombelastograph (TEG) assay with tissue factor and kaolin (TEG TF/K) to measure activated clotting time (ACT) in 31 patients during cardiopulmonary bypass. For comparison, ACTs were also determined by a Hemochron Jr. Signature and a Hepcon HMS. The TEG TF/K correlated with both the Hepcon (r(2) = 0.789) and Hemochron (r(2) = 0.743) ACTs. The average ACT after heparin was 319 +/- 119 s (mean +/- sd) for the TEG TF/K compared with 624 +/- 118 s for the Hepcon instrument. To evaluate the effects of hemodilution on TEG TF/K and Hemochron assays, ACT assays were performed on blood diluted to 50% and titrated with heparin from 0 to 6 U/mL. Both instruments showed significant (P < 0.01) changes in the ACT-versus-heparin slope, but the 0 heparin intercept for the TEG TF/K ACTs was not significantly changed (P = 0.292), in contrast to that for the Hemochron device (P = 0.041). Both instruments also indicated the same 1.3:1 ratio of protamine to heparin for optimum heparin neutralization, with increasing ACTs at ratios >2.6:1. The TEG TF/K ACT assay rapidly monitors heparin anticoagulation, in addition to the capabilities of this instrument to monitor platelet function, clotting factors, and fibrinolysis.