Kiri Victor A
Faculty of Pharmaceutical Sciences, University of Port Harcourt, Choba, Nigeria FV&JK Consulting Ltd, Guildford, UK.
BMJ Open. 2016 Jul 25;6(7):e012105. doi: 10.1136/bmjopen-2016-012105.
Patients with a chronic disease often suffer from other diseases called comorbidities, which can be important factors in the assessment of risks associated with the disease and its management. However, comorbidities can pose important methodological issues because factors such as time, age, duration and the disease can influence their impact on the risk of interest.
To identify comorbidities of a chronic disease, it is common practice to construct 2 separate cohorts of patients-a set with the disease and another as a random sample of patients free of the disease-and compare the event rates for each candidate's comorbidity over a specific period between the 2, while accounting for factors which may confound the results. We describe an incidence-based alternative approach that exploits the longitudinal properties of observational databases to track incident event rates along the natural history of the chronic disease. We illustrate it in a retrospective cohort of patients with chronic obstructive pulmonary disease (COPD) aged 50 and above-each patient with COPD was matched with another without COPD on certain confounding factors.
We obtained 24 079 matched pairs. We found that chronic conditions such as lung cancer, asthma, fracture and osteoporosis were more common in patients with COPD. We also found evidence of time-varying associations.
Our findings in COPD suggest that time is an important factor and comorbidity studies which are based on information in a single fixed period (such as first year postdiagnosis of COPD) are more likely to report spurious associations.
患有慢性病的患者通常还患有其他疾病，即共病，这些疾病可能是评估与该疾病及其管理相关风险的重要因素。然而，共病可能带来重要的方法学问题，因为时间、年龄、病程和疾病等因素会影响它们对所关注风险的影响。
为了识别慢性病的共病，常见的做法是构建两组独立的患者队列——一组患有该疾病，另一组是无该疾病患者的随机样本——并比较两者在特定时间段内每种候选共病的事件发生率，同时考虑可能混淆结果的因素。我们描述了一种基于发病率的替代方法，该方法利用观察性数据库的纵向特性，沿着慢性病的自然病程追踪发病事件率。我们在一个50岁及以上慢性阻塞性肺疾病（COPD）患者的回顾性队列中进行了说明——每个COPD患者在某些混杂因素上与另一名无COPD患者进行匹配。
我们获得了24079对匹配对。我们发现肺癌、哮喘、骨折和骨质疏松等慢性病在COPD患者中更为常见。我们还发现了随时间变化的关联证据。
我们在COPD方面的研究结果表明，时间是一个重要因素，基于单一固定时间段（如COPD诊断后第一年）信息的共病研究更有可能报告虚假关联。
