At any given time, a patient’s blood-glucose level is easy to measure. Beyond the standard pre/postoperative lab values, there are finger sticks, transdermal meters, and other modalities that make taking a patient’s glucose “snapshot” pretty straightforward. So why don’t we surgeons keep track of it more frequently before and after joint replacement, when, according to the prognostic study by Shohat et al. in the July 5, 2018 issue of JBJS, fluctuating glucose levels can have a critical impact on outcomes?
By retrospectively studying more than 5,000 patients who had undergone either total hip or total knee arthroplasty, the authors found that increased variability of glucose levels (measured by a coefficient of variation) was associated with increased risks of 90-day mortality, surgical-site infection, and periprosthetic joint infection. Specifically, the authors demonstrated that for every 10-percentage-point increase in the glycemic coefficient of variation, the risk of 90-day mortality increased by 26%, and the risk of periprosthetic or surgical-site infection increased by 20%. These are remarkable increases in extremely important outcome measures, and the associations held regardless of the patient’s mean glucose values prior to or after the surgery. In fact, some of the highest levels of glucose variability were found in patients who had well-controlled glucose levels preoperatively. Furthermore, as Charles Cornell, MD points out in a commentary on this study, “Glucose variability appears to affect surgical prognosis more than chronic hyperglycemia.”
These findings were surprising and a bit concerning. I don’t tend to order routine blood-glucose measurements postoperatively on patients who appear to be euglycemic based on preoperative testing. Yet, according to these data, maybe I should. Findings of high glucose variability postoperatively might now prompt me to consult with endocrine or perioperative medicine specialists or at least consider informing patients with fluctuating glucose levels that they may be at increased risk of serious postoperative complications.
Measuring a patient’s blood sugar is neither challenging nor prohibitively expensive. So why don’t we monitor it more closely? Probably because, until now, we have not had a compelling reason to do so with “low-risk” patients. What this study suggests is that our definition of a “low-risk” patient from a glycemic-control standpoint may be misinformed. And while further research needs to be performed to corroborate these findings, that is a pretty scary thought to digest.
Chad A. Krueger, MD
JBJS Deputy Editor for Social Media
Patients with diabetes have an increased risk of postoperative complications following total joint arthroplasty (TJA). Additionally, perioperative hyperglycemia has been identified as a common and independent risk factor for periprosthetic joint infection, even among patients without diabetes. Therefore, knowing a patient’s glycemic status prior to surgery is very helpful.
In the November 15, 2017 edition of The Journal of Bone & Joint Surgery, Shohat et al. demonstrate that serum fructosamine, a measure of glycemic control obtainable via a simple and inexpensive blood test, is a good predictor of adverse outcomes among TJA patients—whether or not they have diabetes.
Researchers screened 829 patients undergoing TJA for serum fructosamine and HbA1c—a common measure, levels of which <7% are typically considered good glycemic control. Patients with fructosamine levels ≥292 µmol/L had a significantly higher risk of postoperative deep infection, readmission, and reoperation, while HbA1c levels ≥7% showed no significant correlations with any of those three adverse outcomes. Among the 51 patients who had fructosamine levels ≥292 µmol/L, 39% did not have HbA1c levels ≥7%, and 35% did not have diabetes.
In addition to being more predictive of postsurgical complications than HbA1c, fructosamine is also a more practical measurement. A high HbA1c level during preop screening could mean postponing surgery for 2 to 3 months, while the patient waits to see whether HbA1c levels come down. Fructosamine levels, on the other hand, change within 14 to 21 days, so patients could be reassessed for glycemic control after only 2 or 3 weeks.
While conceding that the ≥292 µmol/L threshold for fructosamine suggested in this study should not be etched in stone, the authors conclude that “fructosamine could serve as the screening marker of choice” for presurgical glycemic assessment. However, because the study did not examine whether correcting fructosamine levels leads to reduced postoperative complications, a prospective clinical trial to answer that question is needed.