Prevalence of aspirin resistance measured by PFA-100

Aspirin protects from cardiovascular events. However, a number of patients who take this drug suffer events, probably due to aspirin resistance. Our objective was to determine the prevalence of aspirin resistance in patients taking this drug and to test if resistance is related to different variables.

Platelet function was studied in 113 patients (90 men) aged 63+/-9 (80 with stable ischaemic heart disease) who took aspirin (100 to 300 mg/day). By a platelet function analyzer, called PFA-100, the epinephrine closure time was studied. We also analysed the possible relationship between epinephrine closure time and the following variables: total cholesterol, LDL, HDL cholesterol, total/HDL cholesterol, triglycerides, lipoprotein(a), and C reactive protein. The possible association between aspirin resistance (epinephrine closure time <161 s) and different variables was also analyzed with the SPSS statistical package. Results are expressed in median (interquartile range).

Aspirin resistance was found in 32% of cases. Ischaemic heart disease, smoking habit, and treatment with statins were associated with a significantly greater percent of resistance (p=0.049, 0.009, and 0.043, respectively). Patients with aspirin resistance had higher levels of total/HDL cholesterol: 4.46 (3.76-5.55) vs. 3.97 (3.20-4.75) (p = 0.023); and lipoprotein(a): 57.2 (24.8-85.0) mg/dl vs. 13.1 (3.7-38.0) mg/dl (p = 0.007).

Aspirin resistance is frequent and easily detected by PFA-100. It occurs more frequently in smokers. A mild association is found with ischaemic heart disease, some lipids, and treatment with statins. Our results support the applicability of this method to clinical practice.