Blood sugar and A1c before hip or knee replacement: why control matters

Diabetes and perioperative hyperglycemia are associated with higher infection and complication risks after hip or knee replacement. That does not mean every elevated A1c requires the same response or that a single cutoff should automatically deny surgery. The useful response is to understand the pattern, improve control when it can be done safely, and coordinate a plan for medicines, fasting, monitoring, and recovery.

The decision also depends on arthritis disability, glucose trends, episodes of low blood sugar, kidney and heart health, nutrition, the urgency and complexity of surgery, and how quickly improvement is realistically possible.

Hemoglobin A1c reflects how much glucose has attached to red blood cells and estimates average exposure over roughly two to three months. It is useful for seeing the longer trend, but it does not show today's value or reveal wide swings between highs and lows.

A finger-stick, laboratory glucose, or continuous glucose monitor reading shows current glucose. Surgical stress, pain, fasting, steroids, infection, and changes in medicine can raise or lower glucose even when the A1c looked acceptable. This is why the preoperative evaluation and the day-of-surgery plan use more than one measure.

High glucose can impair white-blood-cell function and wound healing. Arthroplasty studies consistently associate perioperative hyperglycemia with surgical-site infection and periprosthetic joint infection, although observational studies cannot prove that glucose alone caused each complication.

A systematic review of 17 studies found that inadequate glycemic control was associated with higher surgical-site infection risk after total joint arthroplasty. The authors also found substantial variation between studies and did not support a universal 7% A1c cutoff. That uncertainty is important: risk usually changes along a continuum rather than at one magical number.

In a multicenter retrospective study of 1,645 patients with diabetes having hip or knee replacement, infection rates were higher above an A1c threshold identified by the study as 7.7%. The test's ability to discriminate risk was modest, and the study was not a randomized trial. Its threshold is therefore a useful risk signal, not a universal cancellation rule.

The American Diabetes Association's 2026 hospital-care standards recommend aiming for a preoperative A1c below 8% within three months of elective surgery, while individualizing the risk-benefit assessment. The same guidance advises against postponing surgery based on A1c alone because that can create unnecessary delay or deny needed care.

A1c can look reasonable while glucose is high on the day of surgery or after the operation. In a study of more than 13,000 primary joint replacements, periprosthetic joint infection risk rose as postoperative day-one glucose increased. Another lower-limb arthroplasty cohort found that postoperative hyperglycemia was associated with infection even among patients without a prior diabetes diagnosis.

A large 2023 database study of total hip replacement also found higher infection risk at markedly elevated day-of-surgery glucose levels in patients with and without diabetes. The exact thresholds differed by diabetes status and study design. The practical lesson is to monitor and manage the real-time value rather than relying on A1c as the only gate.

A1c depends on red-blood-cell lifespan. Recent transfusion, blood loss, iron deficiency, some anemias, kidney disease, hemoglobin variants, and other conditions can make it less representative of average glucose. A sudden change in glucose habits may also take time to appear in the A1c.

If the A1c does not fit home readings or symptoms, the medical team may repeat the test, review laboratory factors, use glucose logs or continuous-monitor data, or consider another marker. The goal is to understand actual control—not simply to improve a laboratory number.

Bring a recent A1c, glucose log or continuous-monitor summary when available, a complete medication list, and information about low-glucose episodes. The team should know whether you use insulin, an insulin pump, metformin, a sulfonylurea, an SGLT2 inhibitor, a GLP-1 medicine, steroids, or other drugs that affect glucose.

Kidney function, hydration, eating patterns, prior anesthesia problems, and the timing of the planned procedure can change the medication plan. Some medicines require temporary interruption or dose adjustment, but the instructions are treatment-specific. Do not stop diabetes medicine or change insulin on your own.

Before surgery, ask who is responsible for the diabetes plan and obtain clear instructions for the day before surgery, the fasting period, the morning of surgery, and the first days afterward. The plan should address what to take, what to hold, how often to check glucose, what range should prompt a call, and how to treat a low reading while fasting.

Patients with type 1 diabetes still require basal insulin. Patients using pumps or continuous glucose monitors need a plan that fits the facility's policies and the type of anesthesia and surgery. Continuous glucose monitoring can be helpful, but intraoperative decisions require approved point-of-care or laboratory confirmation.

Rapid intensification can cause hypoglycemia, dehydration, medication side effects, or wide glucose swings. These problems can be especially dangerous in older adults, people with kidney disease, and anyone who does not reliably feel low glucose.

Optimization should improve the overall risk profile, not merely reach a deadline. A thoughtful plan balances the potential benefit of better control against hypoglycemia, surgical delay, immobility, pain, falls, and deconditioning from severe arthritis.

Sometimes a purposeful delay is reasonable—for example, when glucose is severely uncontrolled, symptoms suggest a metabolic emergency, medicine has not been taken safely, or a short period of treatment is likely to reduce risk meaningfully. A delay should come with a diagnosis, treatment plan, follow-up date, and clear responsibility for reassessment.

In other cases, proceeding with enhanced monitoring may be reasonable because the elevation is modest, the trend is improving, hypoglycemia risk limits tighter control, or disability from arthritis is severe. The surgeon, anesthesia team, primary-care clinician, and diabetes clinician should make the decision together with the patient.

Surgical stress triggers hormones that raise glucose. Steroids used for nausea, pain, or inflammation can also increase it. People with prediabetes or no known diabetes may develop temporary postoperative hyperglycemia, and studies show that this can still be associated with infection risk.

Unexpected high glucose should not be dismissed, but it also does not automatically mean permanent diabetes. It may prompt repeat testing, medication review, and follow-up with primary care after recovery.

Regular meals with adequate protein, fiber-rich carbohydrates, and hydration can help reduce large swings before surgery. Crash dieting immediately before joint replacement can worsen nutrition and muscle loss. The JRH surgical nutrition guide and prehab guide can help organize preparation without replacing diabetes care.

Activity within the limits of the painful joint can improve glucose sensitivity, strength, and confidence. Choose exercises that do not create unsafe pain or falls, and ask for physical-therapy guidance when needed.

A concise record helps the orthopedic and medical teams build one coordinated plan:

Seek urgent medical advice for persistent severe hyperglycemia, repeated vomiting, abdominal pain, deep or rapid breathing, confusion, dehydration, or positive ketones. Severe hypoglycemia, loss of consciousness, seizure, or inability to swallow requires emergency treatment.

After joint replacement, call the surgical team for wound drainage, increasing redness, fever, worsening pain, or glucose that remains outside the range in your discharge plan. Call 911 for severe breathing difficulty, chest pain, stroke symptoms, unconsciousness, or another life-threatening emergency.

Turn the laboratory result into a practical plan:

A1c is useful, but it is not the whole story. Current glucose, day-to-day variability, medication safety, low-glucose risk, and the disability caused by arthritis all belong in the decision. Better control can reduce avoidable risk, while a rigid cutoff can oversimplify a complex patient.

Bring your glucose history and complete medication list to an orthopedic consultation or call (808) 439-6201. Dr. Paul Morton can coordinate the joint-replacement plan with the clinicians managing diabetes so the timing and monitoring strategy fit your health.

• American Diabetes Association: Diabetes Care in the Hospital—Standards of Care in Diabetes 2026
• HbA1c threshold and adverse outcomes after total joint arthroplasty
• Glycemic control and surgical-site infection after total joint arthroplasty: systematic review
• Postoperative blood glucose and infection after total joint arthroplasty
• Perioperative hyperglycemia and infection after lower-limb arthroplasty
• Day-of-surgery glucose and infection risk after total hip arthroplasty