Does Baseline Hematocrit Influence Reactivity to Clopidogrel?

In This Article

Abstract and Introduction

Abstract

Background High on-treatment platelet reactivity (HTPR) has been shown to be associated with adverse cardiac events in patients undergoing percutaneous coronary intervention, but the effect of baseline hematologic parameters upon platelet reactivity remains controversial.

Objective The present study aims to evaluate the impact of hematocrit on 2 different assay methods used to assess on-treatment platelet reactivity to clopidogrel.

Methods We tested clopidogrel on-treatment platelet reactivity in 466 consecutive patients using VerifyNow P2Y12 (VN) and light transmission aggregometry (LTA) with adenosine diphosphate (ADP) 5 and 20 μM assays 6 to 24 hours after percutaneous coronary intervention. Patients were categorized into 4 groups according to baseline hematocrit. One-year major adverse cardiac events, including death, nonfatal myocardial infarction, and definite stent thrombosis, were collected.

Results Lower hematocrit was associated with higher P2Y12 reaction unit (PRU) and a higher rate of HTPR (P < .001) as measured by VN assay. No differences were seen among the 4 groups in platelet reactivity measured by LTA using ADP 5 μM (P = .23) and ADP 20 μM (P = .21). In a multivariable logistic regression model, baseline hematocrit was independently associated with PRU ≥208 (odds ratio [OR] 0.92, 95% CI 0.86–0.97, P = .005) but had no correlation with LTA ADP 5 μM ≥46% (OR 1.0, 95% CI 0.95–1.06, P = .88) or LTA ADP 20 μM ≥59% (OR 1.03, 95% CI 0.97–1.09, P = .39). In a logistic regression model, the addition of VN assay results, hematocrit, and interaction between the hematocrit and assay results had shown a significant influence on the area under curve for prediction of 1-year major adverse cardiac events compared with baseline clinical variables only for PRU (0.63 vs 0.76, P = .006) but not with LTA (0.64 vs 0.74, P = .13).

Conclusion Baseline hematocrit has a differential influence on results of the ex vivo platelet functional assays. Lower baseline hematocrit was independently associated with HTPR by VN but not LTA. This may affect the interpretation of platelet function testing in patients with significant anemia.

Introduction

Current guidelines recommend dual antiplatelet therapy, which includes aspirin and a platelet P2Y12 adenosine diphosphate (ADP) receptor antagonist, for treatment of patients with acute coronary syndrome, after percutaneous coronary intervention (PCI) with or without stent implantation.^[1] Currently, there are several techniques that may be used to assess platelet function. The VerifyNow system (VN; Accumetrics, San Diego, CA) is a turbidimetric assay that measures the agglutination of fibrinogen-coated beads to stimulated platelets in citrated whole blood.^[2] The increase in light transmittance, proportional to platelet aggregation, is reported in P2Y12 reaction units (PRUs). The historical "gold standard" is light transmittance aggregometry (LTA), which measures platelet aggregation in platelet-rich plasma in response to certain agonists.^[3] The pharmacodynamic effect of clopidogrel varies substantially among individuals.^[4,5] Studies have identified several patient-related factors that influence this interindividual variability in the response to clopidogrel, as assessed with platelet function assays.^[6,7] The impact of baseline hematologic parameters upon platelet reactivity remains controversial.^[8–10] In the present study, we sought to examine the interaction between the baseline hematocrit upon 2 different ex vivo platelet functional assays in an unselected cohort of patients undergoing PCI.

Table I. Baseline clinical characteristics
Characteristic	Whole group	Hematocrit <39%	Hematocrit ≥39%	P
Age (y)	63 ± 12	66 ± 12	61 ± 11	<.001
Male	338 (73%)	133 (57%)	205 (88%)	<.001
White	333 (72%)	159 (68%)	174 (75%)	.12
African American	108 (23%)	64 (28%)	44 (19%)	.03
Hypertension*	413 (87%)	211 (91%)	202 (87%)	.19
Diabetes mellitus	176 (38%)	107 (46%)	69 (29%)	<.001
Insulin-treated diabetes mellitus	66 (14%)	43 (18%)	23 (10%)	.008
Dyslipidemia^†	415 (89%)	204 (88%)	211 (91%)	.29
Peripheral vascular disease	70 (15%)	49 (21%)	21 (9%)	<.001
History of smoking	265 (57%)	134 (57%)	131 (56%)	.78
Family history of coronary artery disease	227 (49%)	109 (47%)	118 (51%)	.40
Congestive heart failure	56 (12%)	34 (15%)	22 (9%)	.09
Ejection fraction (%)	49 ± 15	49 ± 14	48 ± 16	.60
Body mass index (kg/m²)	30 ± 6	30 ± 7	30 ± 5	.90
Chronic renal insufficiency	78 (17%)	53 (23%)	25 (11%)	<.001
Previous myocardial infarction	134 (29%)	72 (31%)	62 (27%)	.32
Previous coronary artery bypass grafting	115 (25%)	70 (30%)	45 (19%)	.007
Previous angioplasty	212 (46%)	114 (49%)	98 (43%)	.16
Clinical presentation
Stable angina	162 (35%)	85 (37%)	77 (33%)	.43
Unstable angina	242 (52%)	119 (51%)	123 (53%)	.71
Acute myocardial infarction	52 (11%)	23 (10%)	29 (12%)	.38
Procedural characteristics
Bivalirudin	416 (89%)	207 (89%)	209 (90%)	.77
Clopidogrel loading	338 (73%)	100 (72%)	239 (75%)	.47
Platelet count (×10⁹/L)	232 ± 67	237 ± 73	228 ± 60	.19
Hemoglobin (g/dL)	13.2 ± 1.9	11 ± 1.7	14 ± 1.1	<.01
Hematocrit (g/dL)	39 ± 4.2	36 ± 3	43 ± 2	<.001
Medications
Aspirin	454 (98%)	225 (97%)	229 (98%)	.54
Statin	384 (83%)	191 (82%)	193 (84%)	.57
Calcium-channel blocker	87 (19%)	49 (21%)	38 (16%)	.19
Proton pump inhibitors	111 (24%)	34 (24%)	77 (24%)	.94

Values are expressed as n (%) or mean ± SD.
*History of systemic hypertension diagnosed and/or treated with medication or currently being treated with diet and/or medication by a physician.
†Includes patients with a previously documented diagnosis of dyslipidemia. The patient may be treated with diet or medication. A new diagnosis can be made during this hospitalization with an elevated total cholesterol >160 mg/dL. Does not include elevated triglycerides.

Table II. Multivariable correlates of HTPR for VN PRU ≥208, LTA ADP 5 μM ≥46%, and LTA ADP 20 μM ≥59%
Variable	Multivariable correlates PRU ≥208		Multivariable correlates LTA 5 μM ≥46%		Multivariable correlates LTA 20 μM ≥59%
Variable	OR (95% CI)	P	HR (95% CI)	P	HR (95% CI)	P
AA race	1.66 (0.99–2.78)	.05	0.83 (0.50–1.37)	.46	1.34 (0.81–2.24)	.25
Age	1.02 (1.00–1.04)	.03	1.01 (0.99–1.03)	.34	1.02 (1.00–1.04)	.03
Body mass index	1.05 (1.00–1.11)	.01	1.03 (0.99–1.06)	.09	1.04 (1.01–1.08)	.02
Hematocrit	0.92 (0.87–0.97)	.002	1.01 (0.95–1.06)	.84	1.01 (0.96–1.06)	.79
History of CABG	1.39 (0.80–2.42)	.25	0.78 (0.44–1.38)	.39	0.81 (0.46–1.42)	.46
History of CAD	1.42 (0.86–2.35)	.17	1.71 (1.07–2.76)	.03	1.65 (1.02–2.67)	.04
eGFR	1.00 (0.99–1.00)	.29	0.99 (0.99–1.00)	.16	1.00 (0.99–1.00)	.37
Diabetes mellitus	1.43 (0.91–2.26)	.12	1.37 (0.87–2.16)	.18	1.25 (0.80–1.97)	.33
CHF	1.29 (0.63–2.62)	.92	0.69 (0.36–1.33)	.27	0.92 (0.48–1.77)	.80
Unstable angina	0.71 (0.45–1.11)	.13	0.49 (0.31–0.76)	.002	0.52 (0.33–0.81)	.004
Acute MI	1.83 (0.88–3.80)	.11	0.87 (0.43–1.77)	.70	0.95 (0.47–1.94)	.89

Odds ratios and 95% CIs for multivariate analysis are listed for each parameter. Abbreviations: AA, African American; CABG, coronary artery bypass surgery; CAD, coronary artery disease; eGFR, estimated glomerular filtration rate; CHF, congestive heart failure; MI, myocardial infarction.

Table III. Discretionary power of logistic regression model for 1-year composite MACEs
VN P2Y12 PRU	AUC 95% CI	P
Model 1 Clinical variables	0.63
Model 2 Clinical variables + PRU	0.72	.07
Model 3 Clinical variables + hematocrit	0.69	.36
Model 4 Clinical variables + PRU + hematocrit	0.74	.04
Model 5 Clinical variables + PRU + hematocrit + hematocrit and PRU	0.76	.006
LTA MPA 20 μM	AUC 95% CI	P
Model 1 Clinical variables	0.64
Model 2 Clinical variables + LTA	0.72	.14
Model 3 Clinical variables + hematocrit	0.69	.36
Model 4 Clinical variables + LTA + hematocrit	0.76	.07
Model 5 Clinical variables + LTA + hematocrit + hematocrit and LTA	0.74	.13