Comparison of four laboratory methods to assess aspirin sensitivity

A Sticky Situation: Variable Agreement Between Platelet Function Tests Used to Assess Anti-platelet Therapy Response

Background

Platelet function testing to monitor antiplatelet therapy is important for reducing thromboembolic complications, yet variability across testing methods remains challenging. Here we evaluated the agreement of four different testing platforms used to monitor antiplatelet effects of aspirin (ASA) or P2Y₁₂ inhibitors (P2Y12-I).

Methods

Blood and urine specimens from 20 patients receiving dual antiplatelet therapy were analyzed by light transmission aggregometry (LTA), whole blood aggregometry (WBA), VerifyNow PRUTest and AspirinWorks. Result interpretation based on pre-defined cutoff values was used to calculate raw agreement indices, and Pearson's correlation coefficient determined using individual units of measure.

Results

Agreement between LTA and WBA for P2Y12-I-response was 60% (r = 0.65, high-dose ADP; r = 0.75, low-dose ADP). VerifyNow agreed with LTA in 75% (r = 0.86, high-dose ADP; r = 0.75, low-dose ADP) and WBA in 55% (r = 0.57) of cases. Agreement between LTA and WBA for ASA-response was 45% (r = 0.09, high-dose collagen WBA; r = 0.19, low-dose collagen WBA). AspirinWorks agreed with LTA in 60% (r = 0.32) and WBA in 35% (r = 0.02, high-dose collagen WBA; r = 0.08, low-dose collagen WBA) of cases.

Conclusions

Overall agreement varied from 35 to 75%. LTA and VerifyNow demonstrated the highest agreement for P2Y12-I-response, followed by moderate agreement between LTA and WBA. LTA and AspirinWorks showed moderate agreement for aspirin response, while WBA showed the weakest agreement with both LTA and AspirinWorks. The results from this study support the continued use of LTA for monitoring dual antiplatelet therapy, with VerifyNow as an appropriate alternative for P2Y12-I-response. Integration of results obtained from these varied testing platforms with patient outcomes remains paramount for future studies.

Whole Blood Platelet Aggregometry

Light transmittance aggregometry is the historical reference method for platelet function testing and continues to be used extensively. Whole blood impedance lumiaggregometry represents an updated methodology that provides for simplified specimen management, an assay milieu that replicates in vivo platelet activation conditions, improved reproducibility, and near-patient testing. While the impedance-based whole blood aggregometer with luminescence channel is becoming the standard for platelet function testing using this methodology, at least three near-patient whole blood instruments are available, each employing its unique technology. We provide descriptions of whole blood lumiaggregometry and three near-patient systems. We include the principle of operation, materials, and stepwise example protocols and speculate on the importance of concordance among the platforms.

Platelet function testing: from routine to specialist testing

Platelets have many functions within the haemostatic system, and when these actions are diminished for whatever reason, a bleeding tendency can manifest. Unravelling the reason(s) for this bleeding can be complex due to the multiple roles platelets perform. This review seeks to explain each level of platelet testing moving from those performed at local hospital laboratories to those performed by specialist centres and university research departments. It will examine the testing available and discuss when to move on to additional testing.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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%.

CONCLUSIONS

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.

Perioperative assessment of platelet function in patients under antiplatelet therapy

Platelets play a central role in primary hemostasis. Analysis of platelet function is therefore a cornerstone in the global assessment of the coagulation status in the perioperative setting, primarily in patients receiving antiplatelet medication, such as cyclooxygenase-1 inhibitors, adenosine diphosphate antagonists and glycoprotein IIb/IIIa inhibitors. In these patients, knowledge of residual platelet function is highly warranted in order to maintain an optimal and individual balance perioperatively between platelet function and inhibition - that is, bleeding and thrombosis. Traditional laboratory-based assays, such as light-transmission aggregometry and flow cytometry, are the clinical standards of platelet function testing today. Light-transmission aggregometry is one of the most widely used tests to identify and diagnose defects in platelet function. The majority of the conventional laboratory-based techniques are labor intensive, costly and time consuming, and require a high degree of experience and expertise to perform and interpret. Therefore, new automated technologies have been developed to measure platelet function more rapidly and easily, and several techniques can be used at the bedside, including whole blood aggregometry, high shear-induced platelet function assessment or viscoelastic measurement techniques. All methods assessing platelet function are summarized and their limitations are discussed in this article, emphasizing their perioperative use.

Variability and persistence of aspirin response in lower extremity peripheral arterial disease patients

OBJECTIVE

To determine the prevalence of poor response to aspirin (ASA) therapy over 12-month follow-up in patients with lower extremity peripheral arterial disease (PAD), and to compare the classification agreement among different ASA response assays.

METHODS

Patients with PAD on ASA therapy at baseline were included from the ongoing Effect of Lipid Modification on Peripheral Arterial Disease after Endovascular Intervention Trial (ELIMIT), which is a randomized trial testing whether combination treatment with ezetimibe, niacin, and a statin will halt/regress atherosclerosis compared with statin monotherapy. Patients who had baseline platelet testing and repeat testing at 6-month or 12-month follow-up were included. ASA responsiveness was tested using three different assays: Optical aggregation with 0.5 mg/mL of arachidonic acid (AA), optical aggregation with 10 μM of adenosine diphosphate (ADP), and platelet function analyzer-100 (PFA-100) testing with collagen/epinephrine (Epi) loaded cartridges. ASA response was defined as AA aggregation <30%, ADP aggregation <70%, or PFA-100 Epi >164 seconds. Patients who showed response to ASA at baseline were classified as Responders. Poor response to ASA was defined as AA aggregation ≥ 30%, ADP aggregation ≥ 70%, or PFA-100 Epi ≤ 164 seconds. Patients who showed poor response (PR) to an assay at baseline, but then were responsive at follow-up visits were classified as Initial PRs. Patients who showed poor response at baseline and all follow-up visits were classified as Persistent PRs. The classification agreement between assays was tested using the kappa statistic.

RESULTS

Of 102 patients randomized in ELIMIT, 80 patients satisfied inclusion criteria. There were no significant baseline demographic differences between Responders, Initial PRs, and Persistent PRs. The prevalence of persistent poor response varied by the assay used; 5% of subjects (4/80) were Persistent PRs by AA aggregation, compared with 27.5% (22/80) of subjects by ADP aggregation and 9.9% (7/71) of patients by PFA-100 Epi. Regarding the agreement of the assays, only AA aggregation and PFA-100 Epi agreed significantly (K = 0.3223; 95% confidence interval [CI] 0.15-0.493; P = .0001), and though statistically significant, the magnitude of this agreement is small. AA aggregation and ADP aggregation did not agree (K = 0.1161; 95% CI -0.004-0.236; P = .029), nor did ADP aggregation and PFA-100 Epi (K = 0.0044; 95% CI -0.151-0.160; P = .48).

CONCLUSIONS

Between 5% and 27.5% of PAD patients were Persistent PRs to ASA over 6- to 12-month follow-up using different platelet assays. Further, these commonly used platelet assays show weak agreement in determining poor response to aspirin.

Platelet function testing in clinical diagnostics

Although the utility of platelet function testing is still under debate, the necessity to inhibit platelets in patients suffering from cardiovascular and cerebrovascular disease is undoubted and well proven. The wide variety of available platelet function tests often using different methodologies, the apparent lack of standardization, and finally the emerging evidence on the clinical value of platelet function testing are resulting in a considerable uncertainty in the clinical practice, how to deal with the issue of platelet function testing. Platelet function testing might not only yield clinical benefits for the patients but also economical advantages by identifying the right drug at the right dose for the right patient. This article intends to provide an overview of the current platelet function tests such as light transmittance aggregometry, whole blood impedance aggregometry, the PFA-1001 system, the VerifyNow2 system, flow cytometry, as well as other promising technologies like Plateletworks3, IMPACT-R4, PADA, thromboelastography, and the mean platelet component (MPC), briefly addressing strengths, weaknesses and clinical utility of these tests.

Grape polyphenols do not affect vascular function in healthy men

Data suggest that polyphenol-rich products may improve endothelial function and other cardiovascular health risk factors. Grape and wine contain high amounts of polyphenols, but effects of these polyphenols have hardly been investigated in isolation in randomized controlled studies. Our objective in this study was to test the chronic effect of polyphenol-rich solids derived from either a wine grape mix or grape seed on flow-mediated dilation (FMD). Blood pressure and other vascular function measures, platelet function, and blood lipids were secondary outcomes. Thirty-five healthy males were randomized in a double-blind, placebo-controlled crossover study consisting of three 2-wk intervention periods separated by 1-wk washout periods. The test products, containing 800 mg of polyphenols, were consumed as capsules. At the end of each intervention period, effects were measured after consumption of a low-fat breakfast (~751 kJ, 25% fat) and a high-fat lunch (~3136 kJ, 78% fat). After the low-fat breakfast, the treatments did not significantly affect FMD. The absolute difference after the wine grape solid treatment was -0.4% (95% CI = -1.8 to 0.9; P = 0.77) and after grape seed solids, 0.2% (95% CI = -1.2 to 1.5; P = 0.94) compared with after the placebo treatment. FMD effects after the high-fat lunch and effects on secondary outcomes also showed no consistent differences between both of the grape solids and placebo treatment. In conclusion, consumption of grape polyphenols has no major impact on FMD in healthy men. Future studies should address whether grape polyphenols can improve FMD and other cardiovascular health risk factors in populations with increased cardiovascular risk.

Human platelet aggregation and degranulation is induced in vitro by L-thyroxine, but not by 3,5,3'-triiodo-L-thyronine or diiodothyropropionic acid (DITPA)

The endogenous thyroid hormones L-thyroxine (T(4)) and 3,5,3'-triiodo-L-thyronine (T(3)) induce angiogenesis via an endothelial cell iodothyronine receptor on integrin alphaVbeta3. This receptor also exists on platelets. Diiodothyropropionic acid (DITPA) and GC-1, a noniodinated thyroid hormone analog, also induce angiogenesis. Here we examined the effects of iodothyronines (L-T(4) vs L-T(3)) and analogs DITPA and GC-1 on human platelet function. Subthreshold aggregation of platelets obtained from healthy human donors was induced with collagen. Platelet activation (proaggregation) and adenosine triphosphate (ATP) secretion (degranulation) induced by L-T( 4), L-T(4)-agarose, L-T(3), DITPA, or GC-1 were determined simultaneously. Platelet aggregation and ATP secretion induced by a subthreshold level of collagen were enhanced 3-fold by either L-T(4) or L-T( 4)-agarose (0.01 micromol/L) as compared to control, whereas, L-T( 3), DITPA, or GC-1 had no effect under the same conditions. The platelet proaggregatory and degranulation effects of L-T(4) were blocked by the alphavbeta3 antagonist XT199 (0.1 micromol/ L) and by tetraiodothyroacetic acid (tetrac; 0.1 micromol/L). Tetrac inhibits binding of thyroid hormone analogs to the receptor on alphavbeta3 and lacks thyromimetic activity at this site; thus, the proaggregatory action of L-T(4) likely involves the cell surface receptor on integrin alphavbeta3. The thyroid hormone receptor (TR) on human platelets but not endothelial cells distinguishes among iodothyronines, reflecting quantitative differences in integrin sites on endothelial cells and platelets or qualitative differences in the phospholipids/protein microenvironment of endothelial and platelet membranes that can affect integrin function. Additional studies in different populations with larger sample sizes are warranted to determine the impact of the current findings on clinical interventions.

Laboratory assessment and perioperative management of patients on antiplatelet therapy: from the bench to the bedside

The contribution of platelets in the pathophysiology of thromboses has established antiplatelet therapy as a cornerstone for prevention or treatment of these disorders. However, patients on antiplatelet drugs undergoing surgery face the life-threatening dilemma between the risk of perioperative thrombosis by ceasing therapy and restoring platelet function versus the risk of surgical bleeding by its continuation. According to their mechanism of action, antiplatelet drugs can be conventionally classified as agents that inhibit cyclooxygenase, block the platelet adenosine diphosphate P2Y12 receptor, inhibit phosphodiesterase, or block platelet glycoprotein IIb/IIIa. Although several tests have been developed to assess platelet inhibition by most of these compounds, studies to date have not been able to reliably evaluate the diagnostic efficiency of these tests to predict hemorrhage and/or blood loss, and accordingly perioperative assessment of drug-induced platelet inhibition cannot be recommended as yet. Although several management options are available to counteract the hemorrhagic risk of surgical patients using antiplatelet agents, perioperative discontinuation of these drugs is the preferable choice wherever possible. The use of platelet transfusions should be limited where necessary to the treatment of major, life-threatening bleeding. The contribution of newer hemostatic agents, such as desmopressin and recombinant activated factor VII, is yet to be fully determined, and there remain many challenges and unresolved issues in the clinical care of these patients.

[Incidence of aspirin resistance in the patient group of a university hospital in Korea]

BACKGROUND

Aspirin is the most common drug used for the prevention of arterial thrombosis. However, platelet responsiveness to aspirin is variable among individuals and it is important to detect aspirin resistance to improve clinical outcome. We analyzed the changes of platelet reactivity before and after aspirin treatment. We also investigated the incidence and influencing factors of aspirin resistance in Korean.

METHODS

We tested platelet function in 198 patients who had been treated with aspirin in a Korean university hospital, and 59 of these patients were tested for platelet function before and after aspirin treatment. We also analyzed platelet reactivity in 136 patients who had not been treated with aspirin. Platelet function was tested using the VerifyNow Aspirin Assay (Accumetrics, USA). Platelet reactivity was expressed as aspirin reaction unit (ARU) and > or =550 ARU was defined as aspirin resistance.

RESULTS

Platelet reactivity of 136 patients who had not been treated with aspirin was 632.2plusmn;46.3 ARU (meanplusmn;SD) (range, 462-675). Platelet reactivity of 198 patients who had been treated with aspirin was 472.5plusmn;60.0 (338-666) ARU, and 10.1% of patients were aspirin-resistant. The difference of platelet reactivity before and after aspirin treatment was 128.3plusmn;68.7 (-40-248) ARU. Hb level was lower and platelet count was higher in aspirin-resistant group than in aspirin-sensitive group (P<0.05).

CONCLUSIONS

We demonstrated the distribution of platelet reactivity before and after aspirin treatment using the VerifyNow Aspirin Assay. The incidence of aspirin resistance was 10.1%, and low Hb level and high platelet count were related with aspirin resistance.