目的：观察阿司匹林100 mg/d更换为40 mg/d后血小板聚集率变化，评估高龄老年患者对阿司匹林的反应性，分析阿司匹林相关出血的影响因素。方法：入选537例服用阿司匹林100 mg/d（7 d以上）的年龄≥80岁老年患者，根据心血管疾病风险、出血风险评估和花生四烯酸诱导的血小板聚集率（arachidonic acid-induced platelet aggregation，AA-Ag），100例患者更换为阿司匹林40 mg/d。观察阿司匹林更换为40 mg/d的患者AAAg水平及变化，以及3个月内出血情况和上消化道症状变化。结果：537例高龄老年患者服用阿司匹林100 mg/d时的AA-Ag平均10.27%±5.34%（0.42%~28.78%），下四分位数为5.80%；阿司匹林40 mg组减量前AA-Ag平均为5.00%±2.32%，其中71.00%的患者AA-Ag<5.80%。40 mg组患者黑便或便潜血阳性、其他部位出血、上消化道症状和消化道出血史明显高于100 mg组。服用阿司匹林40 mg/d后AAAg增加至11.21%±4.95%（2.12%~28.84%），AA-Ag≥20%者仅为5.00%。多因素分析显示，阿司匹林40 mg AA-Ag与100 mg AA-Ag、体重指数、血小板数正相关,阿司匹林40 mg组中有消化道出血症状的患者比率由减量前的12.00%降低至5.00%，其他部位出血由26.00%降低至8.00%，上消化道症状改善。结论：阿司匹林40 mg/d能够有效抑制高龄老年患者的血小板聚集；100 mg/d改为40 mg/d，患者出血风险降低、上消化道不适症状改善。

Objective： To assess the consequences of switching aspirin dosage from 100 mg/d to 40 mg/d  on cardiovascular benefit, bleeding risk and platelet aggregation in very elderly patients. Methods: Arachidonic acid induced platelet aggregation(AA-Ag) was measured in 537 patients aged 80 or older treated with aspirin (100 mg/d). In the study, 100 patients with low on-treatment platelet aggregation and at high risk of bleeding and low risk of cardiovascular events, were switched to aspirin (40 mg/d) and their platelet aggregation was measured again 7 days later.Their bleeding and upper gastrointestinal symptoms were also recorded in following 3 months. Results: The study observed a heterogeneous distributed aspirin 100 mg/d AA-Ag (range: 0.42% to 28.78%)in the 537 very elderly patients.Aspirin 100 mg/d AA-Ag before the switch in aspirin 40 mg/d group was 5.00%±2.32% and the rate of the patients with low on-treatment platelet aggregation was 71.00%. The rates of melena or occult blood positive, other minimal bleeding,upper gastrointestinal symptoms and a history of gastrointestinal bleeding in 40 mg/d group were higher than those in 100 mg/d group. On a regimen of aspirin 40 mg/d, AA-Ag increased to 11.21%±4.95%(range: 2.12% to 28.84%) with 95.00%of the patients with AA-Ag<20%and the rate of the patients with low on-treatment platelet aggregation was 15.00%. Multiple variable analysis revealed that aspirin 40 mg/d AA-Ag was significantly influenced by aspirin 100 mg/d AA-Ag, BMI and platelet counts. The rate of gastrointestinal bleeding decreased from 12.00% to 5.00%,and upper gastrointestinal symptoms decreased from 59.00% to 21.00% after the switch in 40 mg/d group. Conclusion: Switching aspirin dosage from 100 mg/d to 40 mg/d reduces the bleeding events and improves upper gastrointestinal symptoms, thus inhibiting platelet aggregation effectively in very elderly patients.