A1c before surgery

Why the A1c matters before an operation

The stress of surgery and the hormones it releases raise the risk of high blood sugar, and high blood sugar around surgery is a risk factor for infections and other complications (ADA Standards 2026, sec. 16). The ADA says the evidence supports treating high glucose before admission for planned surgery as a way to reduce bad outcomes (ADA Standards 2026, sec. 16). Current data suggest an optimal A1c between 7% and 8% before surgery, which is linked to better glucose management around the operation and a shorter hospital stay (ADA Standards 2026, sec. 16).

The ADA also notes that many surgical patients have diabetes or prediabetes that may not be known: up to 20% of people having major general surgery have diabetes, and 23% to 60% have prediabetes or undiagnosed diabetes (ADA Standards 2026, sec. 16). For people with diabetes or high glucose who are admitted to hospital, it recommends an A1c test on admission if there is no result from the prior 3 months (ADA Standards 2026, sec. 16). An admission A1c of 6.5% or higher suggests the diabetes started before the hospital stay (ADA Standards 2026, sec. 16) (ADA Standards 2026, sec. 2).

If your A1c is above 8%

Because of a lack of interventional data, the ADA says postponing surgery based on A1c or GMI alone is not recommended, as it may lead to unnecessary delay or to needed surgery being denied (ADA Standards 2026, sec. 16). Some hospitals run optimization programs to lower A1c before elective surgery, and these have been shown to improve glucose management around the operation and shorten the hospital stay (ADA Standards 2026, sec. 16). How fast an A1c can come down is covered in how fast A1c can change. Whether and when to operate is decided by your surgical and diabetes care teams.

Using a sensor instead

If you wear a continuous glucose monitor, the ADA says 14 days of data with a GMI under 8%, or time in range over 50%, may be used in place of A1c as evidence of glucose management before elective surgery (ADA Standards 2026, sec. 16). The GMI estimates A1c from average sensor glucose (Bergenstal 2018); see GMI vs A1c and time in range vs A1c.

During and after surgery

Around the operation, the ADA goal shifts from A1c to blood glucose: 100 to 180 mg/dL (5.6 to 10.0 mmol/L) before, during and after surgery, with goals that may differ by the type of surgery, the risk of low blood sugar and the treatment used (ADA Standards 2026, sec. 16). Stricter goals are not advised because they may not improve outcomes and raise the risk of low blood sugar (ADA Standards 2026, sec. 16). Medicine changes before surgery, such as holding some tablets or adjusting insulin, follow your team's instructions.

Frequently asked questions

What A1c is needed for surgery?

For elective surgery, the ADA Standards of Care 2026 recommend a preoperative A1c goal below 8% (64 mmol/mol), measured within 3 months, with the risk and benefit weighed for each person. The ADA notes that current data suggest an optimal preoperative A1c between 7% and 8%.

Will surgery be cancelled if my A1c is too high?

The ADA says that, because of a lack of interventional data, postponing surgery based on A1c or the glucose management indicator alone is not recommended, as it may lead to unnecessary delay or denial of needed surgery. The surgical team decides, and some hospitals run programs to lower A1c before elective surgery.

Why is A1c checked before surgery?

High blood sugar around the time of surgery is a risk factor for infections and other complications, according to the ADA. An A1c shows how glucose has run over the past few months, and the ADA advises an A1c on hospital admission for people with diabetes or high glucose when none is available from the prior 3 months.

Can a CGM report be used instead of A1c before surgery?

Yes, if available. The ADA says 14-day CGM data with a glucose management indicator below 8%, or time in range above 50%, may be used in place of A1c before elective surgery.