Does Tighter Glycemic Control Beyond Hemoglobin A1c of 8% Improve Outcome for Lumbar Spine Surgery? A MSSIC Study

BACKGROUND AND OBJECTIVES: Diabetes mellitus is associated with increased risk of postoperative adverse outcomes. Previous studies have emphasized the role of glycemic control in postoperative complications. This study aims to ascertain whether controlling hemoglobin A1c (HbA1c) lower than 8% preoperatively results in meaningful risk reduction or improved outcomes. METHODS: We used patient-level data from the Michigan Spine Surgery Improvement Collaborative registry, focusing on patients who underwent elective lumbar spine surgery between 2018 and 2021. The primary outcomes were length of stay and the occurrence of postoperative adverse events. Secondary outcomes included patient satisfaction, achievement of a minimum clinically important difference (MCID) of Patient-Reported Outcomes Measurement Information System-Physical Function, the EuroQol-5D and NRS of leg and back pain, and return to work. RESULTS: A total of 11 348 patients were included in this analysis. Patients with HbA1c above the thresholds before surgery had significantly higher risks of urinary retention for all 3 possible threshold values (incidence rate ratio [IRR] = 1.30, P = .015; IRR = 1.35, P = .001; IRR = 1.25, P = .011 for the HbA1c cutoffs of 8%, 7.5%, and 7%, respectively). They also had longer hospital stay (IRR = 1.04, P = .002; IRR = 1.03, P = .001; IRR = 1.03, P < .001 for the HbA1c cutoffs of 8%, 7.5%, and 7%, respectively) and had higher risks of developing any complication with HbA1c cutoff of 7.5% (IRR = 1.09, P = .010) and 7% (IRR = 1.12, P = .001). Diabetics with preoperative HbA1c above all 3 thresholds were less likely to achieve Patient-Reported Outcomes Measurement Information System MCID at the 90-day follow-up (IRR = .81, P < .001; IRR = .86, P < .001; IRR = .90, P = .007 for the HbA1c cutoffs of 8%, 7.5%, and 7%, respectively) and less likely to achieve EuroQol-5D MCID at the 2-year follow-up (IRR = .87, P = .027; IRR = .84, P = .005 for the HbA1c cutoffs of 7.5% and 7%, respectively). CONCLUSION: Our study suggests that reducing HbA1c below 8% may have diminishing returns regarding reducing complications after spine surgery.