Table 2. Impact on mortality in patients with both COPD and CKD.

COPD: chronic obstructive pulmonary disorder; CRF: chronic renal failure; CKD: chronic kidney disease; OR: odds ratio; HR: hazard ratio; eGFR: estimated glomerular filtration rate; ESRD: end-stage renal disease; CKDcys: chronic kidney disease based on cystatine

Author	Country of patients	Year of publication	Purpose of study	Number of patients	Type of study	Result/mortality with CKD	Conclusion
Suzuki et al. [22]	Yamagata, Japan	2020	Mortality in COPD and CKD	1233 health checkup participants	Cohort	Mortality HR: 2.94 when they have CKD and airflow limitation, 1.29 if only airflow limitation, 1.45 if CKDcys alone	When the two diseases coexist, there is an important risk factor for mortality
Lai et al. [23]	Taiwan	2018	Impact of COPD in advanced CKD	33,399 enrolled, but two similar subgroups with 1820 patients each were created	Cohort	HR 1.22 for mortality	COPD increases the mortality in elderly and males, but not the risk of ESRD
Mukai et al. [24]	Huddinge, Sweden	2018	Correlation of mortality among individuals with normal to severe GFR with lung function	404 individuals with lung function: normal 252, obstructive 42, restrictive 110	Observational	Restrictive lung dysfunction mortality risk sHR: 1.8; no statistically significant obstructive mortality risk. The prevalence of obstructive disease 6% in G1 vs 11% in G5; restrictive 9% in G1 vs 36% in G5	Lung dysfunction is associated with renal function decline
Fabbian et al. [25]	Ferrara, Italy	2016	Relationship between CKD, acute kidney injury and in-hospital mortality in patients admitted for COPD exacerbation	7073 exacerbation COPD patients	Observational retrospective	10.9% CKD prevalence; 5% acute kidney injury	Acute kidney injury is an important factor for in-hospital mortality (OR, 3.849), especially in older males with other comorbidities
Fedeli et al. [26]	Veneto, Italy	2017	Relationship between comorbidities, CKD and mortality in patients with COPD diagnosis	27,272 patients	Cohort	CKD mortality HR: 1.36	Comorbidities and CKD affect the survival of COPD patients
Trudzinski et al. [27]	Germany	2019	Relationship between COPD, CKD, eGFR outcomes and mortality	2274 patients with CKD 161 (7.1%)	Cohort	CKD HR: 2.3	CKD is a relevant comorbidity in COPD patients that affects mortality