Preoperative Platelet Function Testing Research Articles

Center Variation in Use of Preoperative Dual Antiplatelet Therapy and Platelet Function Testing at the Time of Coronary Artery Bypass Grafting in Maryland.

Patients presenting with acute coronary syndrome are administered a P2Y 12 inhibitor and aspirin before coronary catheterization to prevent further myocardial injury from thrombosis. Guidelines recommend a standard waiting period between the time patients are administered dual antiplatelet therapy (DAPT) and elective cardiac surgery. Since 25% to 30% of the population may be considered nonresponders to clopidogrel, platelet function testing can be utilized for timing of surgery and to assess bleeding risks. The extent to which a standard waiting period or platelet function testing is used across centers is not established, representing an important opportunity to standardize practice. We conducted a retrospective cohort study from 2011 to 2020 using data from the Maryland Cardiac Surgical Quality Initiative, a consortium of all 10 hospitals in the state performing cardiac surgery. The proportion of patients administered DAPT within 5 days of surgery was examined by hospital over the time period. Mixed-effects multivariable logistic regressions were used to examine the association of preoperative DAPT with ischemic and bleeding outcomes. Centers were surveyed on use or nonuse of preoperative platelet function testing, and bleeding outcomes were compared. There was significant heterogeneity of preoperative DAPT usage across centers ranging from 2% to 54% ( P < .001). DAPT within 5 days of isolated coronary artery bypass grafting (CABG) was associated with higher odds of reoperation for bleeding (odds ratio [OR], 1.55; 95% confidence interval [CI], 1.19-2.01; P = .001), >2 units of red blood cells (RBCs) transfused (OR, 1.62; 95% CI, 1.44-1.81; P < .001), and >2 units of non-RBCs transfused (OR, 1.79; 95% CI, 1.60-2.00; P < .001). In the 5 hospitals using preoperative platelet function testing to guide timing of surgery, there were greater odds for DAPT within 5 days (OR, 1.33; 95% CI, 1.22-1.45; P < .001), fewer RBCs >2 units transfusions (22% vs 33%; P < .001), and non-RBCs >2 units (17% vs 28%; P < .001) transfusions within DAPT patients. There is significant variability in DAPT usage within 5 days of CABG between hospital centers. Preoperative platelet function testing may allow for earlier timing of surgery for those on DAPT without increased bleeding risks.

Thromboelastography Platelet Mapping—A Useful Preoperative Tool to Reduce Transfusion Requirement by Determining Timing of Coronary Artery Bypass Graft Surgery in Patients taking Dual Antiplatelet Medication: A Pilot Study from Eastern India

AbstractIn this pilot study, we proposed an algorithm to use thromboelastography platelet mapping (TEG-PM) as an effective preoperative platelet function assessment tool in coronary artery bypass graft surgery (CABG) to reduce the transfusion requirement by determining timing of surgery in patients who are on dual antiplatelet therapy (DAPT). Total 15 elective CABG patients who were receiving DAPT were tested by TEG-PM assay after 72 hours’ stoppage of both medications. Four patients who had &lt; 50% inhibition with agonists (arachidonic acid [AA] and adenosine diphosphate [ADP]) were operated within 24 hours of assay. Eight patients who had &gt; 70% inhibition with AA/ADP, surgery was deterred till 48 hours, and 3 patients with &gt; 50% but &lt; 70% inhibition were operated within 24 hours after preoperative prophylactic platelet transfusion. Transfusion requirement was recorded and compared with the previous transfusion data for CABG cases operated without TEG-PM. Distribution of ADP inhibition was 67.54 ± 30.03% and AA inhibition was 60.69 ± 30.14%, showing a variable offset of the effect of both medications starting after 72 hours of cessation. Overall transfusion requirement was decreased by using TEG-PM algorithm. Preoperative platelet function testing to determine the timing of surgery by TEG-PM assay in DAPT-treated patients may be a useful strategy to reduce transfusion requirement in CABG.

Platelet Function Testing in Patients on Antiplatelet Therapy before Cardiac Surgery.

Bleeding and transfusion, common challenges in cardiac surgery, are influenced by comorbidity, the complexity of surgery, hypothermia, and the specifics of cardiopulmonary bypass inducing hemodilution, thrombin generation, fibrinolysis, and platelet dysfunction.1-4 Nearly 11% of patients with acute coronary syndromes undergo coronary artery surgery during dual antiplatelet therapy.5 Although preoperative P2Y12 receptor inhibitor therapy may reduce ischemic events, late preoperative exposure to P2Y12 receptor inhibitors increases the risk of surgery-associated bleeding and reoperation for bleeding.2,6-8.

Point-of-Care Platelet Function Monitoring: Implications for Patients With Platelet Inhibitors in Cardiac Surgery

Although most physicians are comfortable managing the limited anticoagulant effect of aspirin, the recent administration of potent P2Y12 receptor inhibitors in patients undergoing cardiac surgery remains a dilemma. Guidelines recommend discontinuation of potent P2Y12 inhibitors 5- to- 7 days before surgery to reduce the risk of postoperative hemorrhage. Such a strategy might not be feasible before urgent surgery, due to ongoing myocardial ischemia or in patients at high risk for thromboembolic events. Recently, different point-of-care devices to assess functional platelet quality have become available for clinical use. The aim of this narrative review was to evaluate the implications and potential benefits of platelet function monitoring in guiding perioperative management and therapeutic options in patients treated with antiplatelets, including aspirin or P2Y12 receptor inhibitors, undergoing cardiac surgery. No objective superiority of one point-of-care device over another was found in a large meta-analysis. Their accuracy and reliability are generally limited in the perioperative period. In particular, preoperative platelet function testing has been used to assess platelet contribution to bleeding after cardiac surgery. However, predictive values for postoperative hemorrhage and transfusion requirements are low, and there is a significant variability between and within these tests. Further, platelet function monitoring has been used to optimize the preoperative waiting period after cessation of dual antiplatelet therapy before urgent cardiac surgery. Furthermore, studies assessing their value in therapeutic decisions in bleeding patients after cardiac surgery are scarce. A general and liberal use of perioperative platelet function testing is not yet recommended.

Reduction of Preoperative Waiting Time before Urgent Surgery for Patients on P2Y12 Inhibitors Using Multiple Electrode Aggregometry: A Retrospective Study.

P2Y12 inhibitor discontinuation is essential before most surgical interventions to limit bleeding complications. Based on pharmacodynamic data, fixed discontinuation durations have been recommended. However, as platelet function recovery is highly variable among patients, a more individualized approach based on platelet function testing (PFT) has been proposed. The aim of this retrospective single-centre study was to determine whether PFT using whole blood adenosine diphosphate–multiple electrode aggregometry (ADP–MEA) was associated with a safe reduction of preoperative waiting time. Preoperative ADP–MEA was performed for 29 patients on P2Y12 inhibitors. Among those, 17 patients underwent a coronary artery bypass graft. Twenty one were operated with an ADP–MEA ≥ 19 U (quantification of the area under the aggregation curve), and the waiting time was shorter by 1.6 days (median 1.8 days, IQR 0.5–2.9), by comparison with the current recommendations (five days for clopidogrel and ticagrelor, seven days for prasugrel). Platelet function recovery was indeed highly variable among individuals. With the 19 U threshold, high residual platelet inhibition was associated with perioperative platelet transfusion. These results suggest that preoperative PFT with ADP–MEA could help reduce waiting time before urgent surgery for patients on P2Y12 inhibitors.

Association among Clopidogrel Cessation, Platelet Function, and Bleeding in Coronary Bypass Surgery: An Observational Trial.

This study sought to determine (1) the association between the length of preoperative clopidogrel discontinuation, blood loss, and transfusion requirements and (2) whether preoperative platelet function testing predicts excessive postoperative bleeding in patients undergoing coronary artery bypass grafting (CABG) surgery. In this retrospective analysis, patients undergoing CABG were divided into three groups with regard to the period between preoperative clopidogrel cessation and surgery: group 1 (n = 94, ≤3 days), group 2 (n = 100, 4-5 days), and group 3 (n = 83, 6-7 days), respectively. Impedance aggregometry (Multiplate) with arachidonic acid (ASPI) test assay (used for platelets stimulation) and adenosine diphosphate (ADP) test (used for platelets stimulation) was performed before the surgery. Primary outcome was 24 hours chest tube output (CTO) and transfusion requirements (red blood cell concentrate [RBCC], platelet concentrate [PC], fibrinogen concentrate [FC], and fresh-frozen plasma [FFP]) were considered as secondary outcomes. CTO during 24 hours was significantly higher in group 1 as compared with groups 2 and 3, respectively (p = 0.003). Considering secondary outcomes, RBCC (p = 0.043), PC (p = 0.001), FC (p = 0.003), and FFP (p = 0.010) were more frequently transfused in group 1 as compared with groups 2 and 3, respectively. Multiple electrode aggregometry ASPI and ADP tests were significantly correlated with the 24-hour CTO (ASPI test-rho = -0.258, p < 0.001; ADP test-rho = -0.164, p = 0.007). A significant correlation was observed between clopidogrel-free interval and 24-hour CTO (rho = -0.200, p < 0.001). Receiver-operating characteristics (ROC) curve analysis revealed cutoff values to delineate bleeding tendency (ASPI test ≤ 25 area under the aggregation curve [AUC], ADP test ≤63 AUC, and clopidogrel-free interval ≤3 days). Excessive postoperative bleeding occurred less frequently if the period between clopidogrel discontinuation and surgery was longer than 3 days, as compared with shorter waiting time. Inadequate recovery of the platelets function following clopidogrel cessation in preoperative period was associated with increased bleeding risk. Platelet function testing was found to be a useful tool for postoperative bleeding management in our hands.

Is There a Role for Preoperative Platelet Function Testing in Patients Undergoing Cardiac Surgery During Antiplatelet Therapy?

Up to 11% of patients presenting with acute coronary syndromes undergo coronary artery bypass grafting. Guidelines largely recommend a one-size-fits-all preoperative discontinuation period for P2Y12 receptor blockers to avoid bleeding. These recommendations do not account for highly variable pharmacodynamic responsiveness and for variable recovery of platelet reactivity following discontinuation of P2Y12 receptor blockers. Several observational studies have demonstrated that an objective measurement of platelet function among these patients may reduce the waiting period while mitigating the risk of bleeding. Based on these findings, 2 recent guidelines included a Class IIa and IIb recommendation for platelet function testing in patients undergoing cardiac surgery. The following review article describes the rationale for discontinuation of dual antiplatelet therapy before cardiac surgery and the limitations with this approach, available platelet function assays to assess pharmacodynamic effects, and the association between platelet inhibition and other clinical factors with surgery-related bleeding. The information will assist the reader in determining which patients undergoing cardiac surgery might benefit from preoperative platelet function monitoring.

Point-of-care haemostasis and coagulation monitoring in cardiac surgery at IRCCS Policlinico San Donato.

A rational management of perioperative and postoperative bleeding in modern cardiac surgery requires a thorough application of point-of-care (POC) monitoring in order to prevent and readily treat alterations of the haemostatic process. Preoperative platelet dysfunction, residual heparin after extracorporeal circulation, coagulation factors, and/or fibrinogen deficiency could be ruled out and specifically addressed with an appropriate treatment. Our approach includes preoperative platelet function testing of patients administered with thienopyridines or ticagrelor within 7-10 days before planned surgery and platelet function testing-based surgery timing. In the case of postoperative bleeding, residual heparin is tested and additional protamine is eventually administered. Simultaneously, an overall activity of coagulation factors (except fibrinogen) is assessed and, if significantly reduced, correction with prothrombotic complex concentrate is considered. If fibrinogen deficiency is suspected, a specific test is run, and in the case of severe reduction, the deficiency is compensated by fibrinogen concentrate or appropriate volume of fresh-frozen plasma. If both coagulation factors and fibrinogen activity are reduced, fibrinogen is usually considered for correction as first line, followed by prothrombin complex concentrate in the case of further bleeding. It is our clinical practice not to test nor to treat patients until postoperative bleeding appears clinically relevant. At IRCCS Policlinico San Donato, we firmly believe in the importance of the POC-based strategy for haemostatic treatment and constantly update our knowledge through research projects targeted in answering clinically relevant questions.

Effect of Preoperative P2Y12 and Thrombin Platelet Receptor Inhibition on Bleeding After Cardiac Surgery

Background Drugs that act on the platelet P2Y12 receptor are responsible for postoperative bleeding in cardiac surgery. However, protease-activated receptor (PAR) that reacts to thrombin stimulation might still be active in patients treated with P2Y12 inhibitors. Preoperative platelet function testing could possibly guide the timing of surgery. We investigated the association between P2Y12 receptor and PAR inhibition and bleeding after cardiac surgery. Methods A retrospective cohort study of 361 patients undergoing cardiac surgery and treated with P2Y12 anti-platelet agents was undertaken. All patients received a preoperative multiplate electrode aggregometry testing of platelet P2Y12 receptor activity (ADPtest) and PAR reactivity with thrombin receptor-activating peptide (TRAP) stimulation. ADPtest and TRAPtest data measured before surgery were analysed for association with postoperative bleeding (ml per 12 h) and severe postoperative bleeding. Results Both the ADPtest and the TRAPtest were significantly (P=0.001) associated with postoperative bleeding. A threshold of 22 U for the ADPtest yielded a negative predictive value (NPV) of 94% and a positive predictive value (PPV) of 20%, and a threshold of 75 U for the TRAPtest yielded an NPV of 95% and a PPV of 23%. In the subgroup of patients with ADPtest Conclusions In patients taking P2Y12 receptor inhibitors, residual platelet reactivity to thrombin stimulation limits the risk of severe postoperative bleeding.

The role of point-of-care assessment of platelet function in predicting postoperative bleeding and transfusion requirements after coronary artery bypass grafting

Objective:Objective platelet function assessment after cardiac surgery can predict postoperative blood loss, guide transfusion requirements and discriminate the need for surgical re-exploration. We conducted this study to assess the predictive value of point-of-care testing platelet function using the Multiplate® device.Methods:Patients undergoing isolated coronary artery bypass grafting were prospectively recruited (n = 84). Group A (n = 42) patients were on anti-platelet therapy until surgery; patients in Group B (n = 42) stopped anti-platelet treatment at least 5 days preoperatively. Multiplate® and thromboelastography (TEG) tests were performed in the perioperative period. Primary end-point was excessive bleeding (>2.5 ml/kg/h) within first 3 h postoperative. Secondary end-points included transfusion requirements, re-exploration rates, intensive care unit and in-hospital stays.Results:Patients in Group A had excessive bleeding (59% vs. 33%, P = 0.02), higher re-exploration rates (14% vs. 0%, P < 0.01) and higher rate of blood (41% vs. 14%, P < 0.01) and platelet (14% vs. 2%, P = 0.05) transfusions. On multivariate analysis, preoperative platelet function testing was the most significant predictor of excessive bleeding (odds ratio [OR]: 2.3, P = 0.08), need for blood (OR: 5.5, P < 0.01) and platelet transfusion (OR: 15.1, P < 0.01). Postoperative “ASPI test” best predicted the need for transfusion (sensitivity - 0.86) and excessive blood loss (sensitivity - 0.81). TEG results did not correlate well with any of these outcome measures.Conclusions:Peri-operative platelet functional assessment with Multiplate® was the strongest predictor for bleeding and transfusion requirements in patients on anti-platelet therapy until the time of surgery. Study registration: ISRCTN43298975 (http://www.controlled-trials.com/ISRCTN43298975/).

Effect of preoperative P2Y12 and thrombin platelet receptor inhibition on bleeding after cardiac surgery

Drugs that act on the platelet P2Y12 receptor are responsible for postoperative bleeding in cardiac surgery. However, protease-activated receptor (PAR) that reacts to thrombin stimulation might still be active in patients treated with P2Y12 inhibitors. Preoperative platelet function testing could possibly guide the timing of surgery. We investigated the association between P2Y12 receptor and PAR inhibition and bleeding after cardiac surgery. A retrospective cohort study of 361 patients undergoing cardiac surgery and treated with P2Y12 anti-platelet agents was undertaken. All patients received a preoperative multiplate electrode aggregometry testing of platelet P2Y12 receptor activity (ADPtest) and PAR reactivity with thrombin receptor-activating peptide (TRAP) stimulation. ADPtest and TRAPtest data measured before surgery were analysed for association with postoperative bleeding (ml per 12 h) and severe postoperative bleeding. Both the ADPtest and the TRAPtest were significantly (P=0.001) associated with postoperative bleeding. A threshold of 22 U for the ADPtest yielded a negative predictive value (NPV) of 94% and a positive predictive value (PPV) of 20%, and a threshold of 75 U for the TRAPtest yielded an NPV of 95% and a PPV of 23%. In the subgroup of patients with ADPtest <22 U, TRAPtest ≥75 U was not associated with severe bleeding (NPV of 100% and PPV of 37%). In patients taking P2Y12 receptor inhibitors, residual platelet reactivity to thrombin stimulation limits the risk of severe postoperative bleeding.

Preoperative point-of-care platelet function testing in cardiac surgery.

To investigate if the use of preoperative platelet function testing (PFT) as part of a transfusion algorithm reduced blood product usage in coronary artery bypass surgery (CABG). Prospective, randomized, controlled trial. A cardiothoracic hospital. 249 patients having CABG surgery. The patients were allocated randomly to PFT preoperatively with Multiple Electrode Aggregometry (MEA, Group A), TEG PlateletMapping (PM, Group B) or none (control, Group C). Post-bypass bleeding management was determined by a transfusion algorithm. The primary outcome measure was blood product transfusion in the first 48 hours post-surgery. There was a significant reduction in all blood product transfusion between Groups A (MEA) and B (PM) and Group C (control) (median number of units transfused, 2 (A)/2 (B)/ 4(C), p=0.02). Those in A and B received fewer units of red cells (median number of units, 0 (A)/1 (B) /2 (C), p=0.006) and fresh frozen plasma than the control Group C (median number of units, 0 (A)/0 (B)/2 (C), p<0.001), without receiving significantly more units of platelets (median number of units, 1 (A)/1 (B)/0 (C), p=0.11). In those who had taken an adenosine disphosphate (ADP)-receptor antagonist within 5 days (n=173), these results were amplified, and additionally, there was a significant cost saving (median cost, A=£1738.53, B=£1736.96, C=£3191.80 p=0.006). Preoperative PFT as part of a point-of-care testing-based transfusion algorithm led to a reduction in blood transfusion. There is a potential cost saving in those who have taken an ADP-receptor antagonist within 5 days.

TCT-121 Relationship Between On-treatment Platelet Reactivity Prior to Coronary Artery Bypass Surgery and In-Hospital Major Bleeding The Surgical Timing based On Platelet Reactivity for Coronary Artery Bypass Graft surgery (STOP-CABG) trial

Use of aspirin plus thienopyridine increases bleeding risk of coronary artery bypass graft (CABG) surgery. In STOP-CABG trial we prospectively evaluated the association between the pre-operative platelet function testing by different assay methods on the occurrence of post CABG bleeding. 81

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Platelet activity measured by a rapid turnaround assay identifies coronary artery bypass grafting patients at increased risk for bleeding and transfusion complications after clopidogrel administration

We sought to establish a metric for easily estimating bleeding and transfusion risks for cardiac surgery patients after antiplatelet agent use. Deidentified records of patients who underwent coronary artery bypass grafting (CABG) at our institution (January 2010-June 2011) were searched for patients without identified risk factors for excessive bleeding who underwent documented P2Y12 testing after clopidogrel administration (n=276). Clinical outcomes were analyzed according to whether preoperative platelet function was higher (platelet reactivity units [PRUs], ≥237) or lower (PRU, <237) and according to preoperative PRU cutoffs: high (>290, or no clopidogrel), intermediate (200-290), or low (<200). Eighty-five patients (57%) received allogeneic blood products at 24 hours or less postoperatively: 33 (22%) received fresh frozen plasma, and 57 (38%) received platelets. The median 12-hour chest tube output (CTO) was 350 mL (interquartile range, 260-490 mL); CTO was "high" (>437 mL) in 62 (42%) of the clopidogrel-treated patients. Lower-PRU patients were more likely to receive coagulation factors (odds ratio [OR], 2.82; P=.0004) and to have high CTO or coagulation factor transfusion (OR, 2.35; P=.02) than higher-PRU patients. Likewise, intermediate- and low-PRU patients had incrementally greater incidences of high CTO (OR, 1.72; P=.002) and coagulation factor transfusion (OR, 2.08; P<.0001) than high-PRU/no clopidogrel patients. High CTO or coagulation factor transfusion was more frequent in intermediate-PRU (OR,2.67; P=.02) and low-PRU (OR, 5.08; P=.0002) patients than in high-PRU/no clopidogrel patients. Among clopidogrel-treated CABG patients, preoperative platelet function testing can identify those at increased risk for postoperative bleeding and transfusion.

Platelet Function Measurement–Based Strategy to Reduce Bleeding and Waiting Time in Clopidogrel-Treated Patients Undergoing Coronary Artery Bypass Graft Surgery

Aspirin and clopidogrel therapy is associated with a variable bleeding risk in patients undergoing coronary artery bypass graft surgery (CABG). We evaluated the role of platelet function testing in clopidogrel-treated patients undergoing CABG. One hundred eighty patients on background aspirin with/without clopidogrel therapy undergoing elective first time isolated on-pump CABG were enrolled in a prospective single-center, nonrandomized, unblinded investigation (Timing Based on Platelet Function Strategy to Reduce Clopidogrel-Associated Bleeding Related to CABG [TARGET-CABG] study) between September 2008 and January 2011. Clopidogrel responsiveness (ADP-induced platelet-fibrin clot strength [MA(ADP)]) was determined by thrombelastography; CABG was done within 1 day, 3-5 days, and >5 days in patients with an MA(ADP) >50 mm, 35-50 mm, and <35 mm, respectively. The primary end point was 24-hour chest tube drainage and key secondary end point was total number of transfused red blood cells. Equivalence was defined as ≤25% difference between groups. ANCOVA was used to adjust for confounders. Mean 24-hour chest tube drainage in clopidogrel-treated patients was 93% (95% confidence interval, 81-107%) of the amount observed in clopidogrel-naive patients, and the total amount of red blood cells transfused did not differ between groups (1.80 U versus 2.08 U, respectively, P=0.540). The total waiting period in clopidogrel-treated patients was 233 days (mean, 2.7 days per patient). A strategy based on preoperative platelet function testing to determine the timing of CABG in clopidogrel-treated patients was associated with the same amount of bleeding observed in clopidogrel-naive patients and ≈50% shorter waiting time than recommended in the current guidelines. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00857155.

Multiple Electrode Whole Blood Aggregometry, PFA-100, and In Vivo Bleeding Time for the Point-of-Care Assessment of Aspirin-Induced Platelet Dysfunction in the Preoperative Setting

Acquired platelet dysfunction due to aspirin ingestion may increase bleeding tendency during surgery. Thus, we examined the diagnostic accuracy of in vivo bleeding time (BT) and 2 platelet function assays for the preoperative assessment of a residual antiplatelet effect in patients treated with aspirin. Consecutive patients scheduled for surgery were prospectively enrolled in this study. The patients' last aspirin ingestion had occurred within the previous 48 hours before blood sampling in the "full aspirin effect" group, between 48 and 96 hours before in the "variable aspirin effect" group, and >96 hours before in the "recovered aspirin effect" group. The control group had not taken any aspirin. Multiple electrode aggregometry, platelet function analyzer (PFA)-100, and in vivo BT were performed to assess the effects of aspirin. One-way analysis of variance on ranks with a post hoc multiple-comparison procedure (Dunn) was used to detect differences among the groups. Categorical data were compared using the z test. Receiver operating characteristic (ROC) curves were created to determine the diagnostic accuracy of the platelet function assays investigated. The area under the ROC curve (AUC), sensitivity, and specificity of the assays were calculated. The level of statistical significance was set at P < 0.05. Three hundred ninety-four patients were included in the analysis (133 control and 261 aspirin-treated patients). All 3 methods were able to detect the antiplatelet effect of aspirin in the full aspirin effect group. Furthermore, no difference in the measurement values between the recovered aspirin effect and control group was found, irrespective of the assay performed. Measurement values in the variable aspirin effect group were different from those of the control group in the ASPItest using multiple electrode aggregometry and COL-EPI using PFA-100 but not in BT. ROC analysis showed the highest diagnostic accuracy in excluding the residual aspirin effect in the ASPItest (AUC 0.81, P < 0.001), followed by COL-EPI (AUC 0.78, P < 0.001) and BT (AUC 0.56, P = 0.05). The cutoff value of 53 U in the ASPItest excluded the effect of aspirin with a sensitivity of 88% and specificity of 71%. The full therapeutic antiplatelet effects of aspirin can be expected within 48 hours of the patient's last aspirin ingestion. Platelet function recovered in our study if aspirin cessation occurred >96 hours (4 days) before; thus, in these patients, preoperative platelet function testing is not useful. To quantify any residual aspirin effect in patients who ceased their intake of aspirin between 48 and 96 hours before surgery, the ASPItest might have the highest diagnostic accuracy.