GSTM1 and chronic obstructive pulmonary disease: THA: total hip arthroplasty; TKA: total knee arthroplasty; UKA: unicompartmental knee arthroplasty; SD: standard deviation; Hb: haemoglobin; CKD: chronic kidney disease; COPD: chronic obstructive pulmonary disease; MI: myocardial infarction; GI: gastrointestinal