Clinically-defined preoperative serum phosphorus abnormalities and outcomes of coronary artery bypass grafting: Retrospective analysis using inverse probability weighting adjustment

BACKGROUND: Serum phosphorus is a well-known marker of vascular calcification, but the effects of serum phosphorus abnormalities defined by clinical criteria on the outcomes of coronary artery bypass grafting (CABG) remain unclear. We aimed to evaluate whether preoperative serum phosphorus abnormalities defined based on clinical criteria are associated with outcomes of CABG using a relatively new statistical technique, inverse probability weighting (IPW) adjustment. METHODS: From January 2001 to December 2014, 4,989 consecutive patients who underwent CABG were stratified into normal (2.5-4.5 mg/dl; n = 4,544), hypophosphatemia (<2.5 mg/dl; n = 238), or hyperphophatemia (>4.5 mg/dl; n = 207) groups depending on preoperative serum phosphorus level. RESULTS: The primary outcome was all-cause death during a median follow-up of 48 months. Secondary outcomes were cardiovascular death, graft failure, myocardial infarction, repeat revascularization, and stroke. In multivariate Cox analysis, preoperative hypophosphatemia was significantly associated with all-cause death (hazard ratio [HR] 1.76; 95% confidence interval [CI] 1.13-2.76; P = 0.01). However, this association varied depending on chronic kidney disease and emergent operation (p for interaction = 0.05 and 0.03, respectively). In addition, analysis after IPW adjustment demonstrated that preoperative serum phosphorus abnormalities were not significantly associated with all-cause death (P = 0.08) or any secondary outcomes except graft failure. Graft failure was significantly associated with preoperative hypophosphatemia (HR 2.51; 95% CI 1.37-4.61; P = 0.003). CONCLUSION: Our study showed that preoperative serum phosphorus abnormalities in clinical criteria were not associated with outcomes after CABG except for graft failure. And, the association of hypophosphatemia with graft failure remains to be evaluated.