The high prevalence of multimorbidity among middle-aged and older adults has become a serious issue needing to be addressed by China's healthcare system. The number of chronic diseases is related to health service utilization and medical costs, but there is still a lack of relevant national surveys in China.

To understand the prevalence and features of multimorbidity and to examine its associations with health service utilization and medical costs among middle-aged and older Chinese adults.

Data were collected from the 2018 wave of China Health and Retirement Longitudinal Study (CHARLS) during April to October 2021, involving 16 674 Chinese adults (≥45 years old) . Multimorbidity was defined as the coexistence of two or more of the self-reported 14 chronic conditions. Health service utilization was measured using inpatient service utilization in the past year and outpatient service utilization in the past month. Medical costs were measured using total inpatient cost and out-of-pocket (OOP) cost for inpatient care in the past one year, total outpatient costs and OOP cost for outpatient care in the past one month. Logistic regression was used to estimate the association between the number of chronic diseases and health service utilization. Quantile regression was adopted to estimate the association between the number of chronic diseases and medical costs.

Of all participants, 9 561 (57.34%) had multimorbidity. 2 624 (15.74%) had utilized inpatient services in the past year, and 2 588 (15.52%) used outpatient services in the past one month. Inpatient service utilization, outpatient service utilization, total inpatient cost, OOP cost for inpatient care, total outpatient cost, and OOP cost for outpatient care varied significantly by the number of chronic diseases (P<0.05) . Multivariate Logistic regression analysis indicated that the number of chronic diseases was associated with inpatient service utilization (P<0.05) . Suffering from 1, 2, 3, 4 and ≥5 chronic diseases was associated with 1.882 times〔95%CI (1.547, 2.290) 〕, 2.939 times〔95%CI (2.429, 3.555) 〕, 4.231 times〔95%CI (3.490, 5.130) 〕, 5.723 times〔95%CI (4.680, 7.000) 〕, and 8.671 times〔95%CI (7.173, 10.482) 〕 higher rate of inpatient service utilization, respectively. Having 1, 2, 3, 4 and ≥5 chronic diseases was associated with 1.684 times〔95%CI (1.421, 1.995) 〕, 2.481 times〔95%CI (2.101, 2.931) 〕, 3.691 times〔95%CI (3.115, 4.374) 〕, 3.774 times〔95%CI (3.134, 4.544) 〕, and 5.577 times〔95%CI (4.698, 6.620) 〕 higher rate of outpatient service utilization, respectively. Each increased chronic disease was associated with an increase in both total inpatient costs and OOP for inpatient care at the upper and middle (50, 75 and 90 percentiles) percentile levels, with larger effects on the upper percentile 〔90th percentile Coeff (95%CI) =1 248.43 (219.20, 2 277.66) for total hospital costs; 90th percentile Coeff (95%CI) =706.36 (266.87, 1 145.86) for OOP for inpatient care〕. Each increased chronic disease was also associated with an increase in both total outpatient costs and OOP for outpatient care, and the effects on the upper percentiles were larger〔90th percentile Coeff (95%CI) =196.33 (31.06, 361.61) for total outpatient costs; 90th percentile Coeff (95%CI) =128.56 (26.83, 230.28) for OOP for outpatient care〕.

In middle-aged and older Chinese adults, multimorbidity was highly prevalent, and the increase in the number of coexisted chronic diseases was associated with higher rate of health service utilization and medical costs. The government should pay more attention on primary care to manage the demand for health services and medical costs associated with multimorbidity.

中老年人慢性病共病情况严重，已成为我国卫生体系面临的重要问题。慢性病患病数量与卫生服务利用和医疗费用相关，但目前我国尚缺乏该方向研究的全国性调查。

了解我国中老年人慢性病共病的患病情况和特征，分析患慢性病数量对中老年人卫生服务利用和医疗费用的影响。

于2021年4—10月，在中国健康与养老追踪调查（CHARLS）2018年数据库中获取16 674例≥45岁受访者的问卷资料。问卷中设置了14种慢性病，以受访者自我报告患≥2种慢性病为存在慢性病共病。选取的卫生服务利用指标为受访者过去1年是否利用过住院服务、过去1个月是否利用过门诊服务，选取的医疗费用指标为过去1年的住院总费用和住院自付费用、过去1个月的门诊总费用和门诊自付费用。采用Logistic回归分析慢性病患病数量对卫生服务利用的影响，采用分位数回归分析慢性病患病数量对医疗费用的影响。

在16 674例中老年人中，9 561例（57.34%）患≥2种慢性病（慢性病共病），2 624例（15.74%）在过去1年利用过住院服务，2 588例（15.52%）在过去1个月利用过门诊服务。不同慢性病患病种数患者的住院服务利用率、门诊服务利用率，以及住院总费用、住院自付费用、门诊总费用、门诊自付费用比较，差异有统计学意义（P<0.05）。多因素Logistic回归分析结果显示，慢性病患病种数是中老年人住院服务利用的影响因素，患1、2、3、4、≥5种慢性病患者的住院服务利用率分别是未患慢性病者的1.882倍〔95%CI（1.547，2.290）〕、2.939倍〔95%CI（2.429，3.555）〕、4.231倍〔95%CI（3.490，5.130）〕、5.723倍〔95%CI（4.680，7.000）〕、8.671倍〔95%CI（7.173，10.482）〕，门诊服务利用率分别是未患慢性病者的1.684倍〔95%CI（1.421，1.995）〕、2.481倍〔95%CI（2.101，2.931）〕、3.691倍〔95%CI（3.115，4.374）〕、3.774倍〔95%CI（3.134，4.544）〕、5.577倍〔95%CI（4.698，6.620）〕。分位数回归分析结果显示：每增加1种慢性病，第50、75、90百分位数下的住院总费用和住院自付费用增加，且对上百分位数费用水平的影响更大〔住院总费用第90百分位Coeff（95%CI）=1 248.43（219.20，2 277.66），住院自付费用第90百分位Coeff（95%CI）=706.36（266.87，1 145.86）〕；每增加1种慢性病，各百分位数下的门诊总费用和门诊自付费用均增加，且对上百分位数的影响更大〔门诊总费用第90百分位Coeff（95%CI）=196.33（31.06，361.61），门诊自付费用第90百分位Coeff（95%CI）=128.56（26.83，230.28）〕。

我国中老年人的慢性病共病情况严重，慢性病患病种数增加与更高的卫生服务利用和医疗费用相关。政府应重视初级保健，以管理与慢性病共病有关的卫生服务需求和医疗费用。