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Insulin on the day of your cancer operation | CION Cancer Clinics
If you use insulin, you will usually be given a changed dose for the evening before and the morning of surgery, not told to stop it. Fasting makes your usual dose risky, and the operation itself pushes sugar up. Your anaesthetist or diabetes doctor sets the plan. This page explains what that plan depends on, how to spot a low sugar, and what to ask. CION Cancer Clinics’ surgical oncologists in Hyderabad can talk this through with you.
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Medically reviewed by Dr. Muralidhar MuddusettyConsultant Surgical Oncologist · MBBS (AIIMS), MS (Surgery, AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh) · last reviewed September 2026, next review due September 2027
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On this page
- Do you take your insulin on the morning of surgery?
- Which kind of insulin are you on?
- How do you get a clear insulin plan before surgery?
- What do the diabetes terms on your chart mean?
- What do families get wrong about insulin before an operation?
- What happens to your insulin after surgery?
- Common questions about insulin on the day of surgery
The short answer
Do you take your insulin on the morning of surgery?
Most people who use insulin are not asked to stop it completely, but the dose on the day before and the morning of surgery is usually changed. Your anaesthetist or diabetes doctor will give you a written plan for exactly what to take, and that plan is the only one to follow.
Why the dose changes at all
You will be fasting before the operation. Insulin lowers blood sugar whether you have eaten or not, so your usual dose on an empty stomach can pull your sugar too low. At the same time, the stress of an operation pushes sugar up. Your team is trying to keep you in a safe middle range on both sides of that.
Why the plan is different for everyone
The right change depends on which insulin you use, how many times a day you inject, how well controlled your sugar has been, what time of day your operation is listed, and how long you are likely to be unable to eat afterwards. Two people on the same insulin can be given quite different instructions, and both can be correct.
What this page will not do
It does not give doses, units or timings. Those depend on your own readings and your operation, and a number from a website can do real harm. What it can do is help you ask the right questions and understand the answers.
Never skip or change your insulin on your own before surgery. Ask first, even the night before.Know your insulin
Which kind of insulin are you on?
Your plan depends on this more than anything else. Take the pens, vials or cartridges to your pre-surgery check so the team can read the names themselves.
Long-acting, once or twice a day
This is the background insulin that works across the whole day and night. Common names include glargine (Lantus, Basalog), degludec (Tresiba) and detemir. It is often continued in some form, because it covers the body's basic needs even when you are not eating.
Premixed insulin
A mix of short and longer-acting insulin in one pen, very common in India. Names include Mixtard, Human Mixtard, NovoMix and Humalog Mix. Because part of it is meant to cover meals, it usually needs the biggest change on a fasting day.
Rapid or short-acting, with meals
Taken just before food to cover that meal. Examples are aspart (NovoRapid), lispro (Humalog) and regular human insulin (Actrapid). If there is no meal, the team will tell you what to do with this dose.
Insulin pump or a combination with tablets
Pumps need their own plan, often agreed with your diabetes doctor well before the day. If you also take tablets such as metformin or a gliflozin, those have separate instructions too.
Tablets for diabetes are covered on their own page in this section.Not sure whether this applies to you?
Ask an oncologistBefore the day
How do you get a clear insulin plan before surgery?
Bring your readings
Take your glucose diary or meter to the pre-anaesthetic check, along with your latest HbA1c report. The team wants to see your usual pattern, including any lows, not just one good reading.
Name every insulin and the time you take it
Say the brand, how many times a day you inject and when. If a family member gives the injections, bring them to this appointment so they hear the plan too.
Ask for the plan in writing
Ask for the changes to the evening before and the morning of surgery to be written down, in your language if possible. Ask who to call if the operation time moves.
Check on the morning
Check your sugar when you wake up and again before leaving home, and write the numbers down. Tell the nurse at admission what you took and when, even if it matched the plan exactly.
!
Low sugar while fasting cannot wait
If you feel shaky, sweaty, confused, very hungry or have a pounding heart while fasting, check your sugar straight away. If it is low, treat it with the sugary drink or glucose your team told you to keep ready, even though you are fasting. Then call the hospital and tell them. A delayed operation is far better than an untreated low sugar, and nobody will be angry that you drank something.
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Words you will hear
What do the diabetes terms on your chart mean?
- HbA1c
- A blood test that shows your average sugar over the last few months. A high result may lead the team to improve control before a planned operation.
- Hypoglycaemia
- Blood sugar that has dropped too low. This is the main risk of taking your usual insulin while not eating.
- Insulin drip or infusion
- Insulin given slowly through a line in your arm, with sugar checked often and the rate adjusted. It is common during and after larger operations.
- Sliding scale
- An older name for an insulin drip or for extra insulin given according to your sugar reading. You may still hear it on the ward.
- Capillary blood glucose
- A finger-prick sugar test. After surgery the nurses will do this many times a day until you are eating normally.
Commonly believed
What do families get wrong about insulin before an operation?
"No food means no insulin, so skip it altogether."
Stopping all insulin can let your sugar climb very high, and in people with type 1 diabetes it can become dangerous quickly. The body still needs background insulin when you fast. Follow the changed dose you were given, not a full stop.
"Take the full dose so the sugar is perfect for the doctors."
A full dose on an empty stomach is the most common route to a low sugar on the morning of surgery. Slightly higher readings on the day are expected, and the team is ready to manage them.
"If my sugar is high on the day, the operation is cancelled."
Not always. The team looks at how high it is, how you are otherwise, and how urgent the operation is. Many people with raised readings still go ahead with an insulin drip.
After the operation
What happens to your insulin after surgery?
Straight after surgery your sugar will be checked often, and insulin is usually given through a drip or by injection according to your readings. You go back to your own insulin once you are eating and drinking reasonably, and the team decides when that is.
Why sugar can run high for a while
Pain, the stress of the operation, an infection, steroids or feeding through a tube can all push sugar up, even in people whose control was good before. For a time you may need more insulin than usual, or insulin when you normally manage on tablets. This usually settles as you recover.
Who this general pattern does not fit
People with type 1 diabetes, people on pumps, pregnant women, children, and anyone who has had operations on the pancreas, stomach or bowel often need a very individual plan. The same applies if your kidneys are not working well. Ask specifically about your situation.
Questions we are asked
Common questions about insulin on the day of surgery
Can I take my long-acting insulin the night before?
Often yes, but frequently at a reduced dose. It depends on your usual readings, whether you tend to get lows at night, and the time of your operation. Ask at your pre-anaesthetic check and get the answer written down. Do not reduce or skip it on your own guesswork.
What if my operation is in the afternoon?
Afternoon lists sometimes allow a light early breakfast, which changes the insulin plan. Some centres let you take a partial dose with that meal. Your team will tell you, and they should also tell you what to do if the operation is moved later or earlier on the day.
Can I drink water or juice while fasting?
Clear fluids are often allowed until a set time before surgery, and your team gives you that time. Glucose drinks may be allowed if your sugar drops. Milk, tea with milk and fruit juice with pulp are usually not allowed. Follow the exact fasting instructions from your anaesthetist.
My sugar was high on the morning of surgery. What happens now?
Tell the admitting nurse immediately and show your readings. The team will check your blood and urine, and may start an insulin drip. Whether the operation goes ahead depends on the level, how you feel and how urgent the surgery is. That decision belongs to the anaesthetist and surgeon.
Should I bring my insulin pens to the hospital?
Yes. Bring them in their box with the label, along with your meter and diary. The ward may use its own supply, but seeing your exact insulin helps avoid mistakes. Do not inject from your own pen in hospital unless a nurse has agreed it.
Will my diabetes make the surgery riskier?
Poorly controlled diabetes can slow wound healing and raise the chance of infection. Good control before a planned operation helps. Your surgeon and anaesthetist weigh your sugar control alongside your heart, kidneys and the operation itself. Ask them what it means for you specifically.
My father forgets and took his usual dose. What should we do?
Call the hospital straight away and tell them what was taken and when. Check his sugar now and keep checking it. Keep glucose ready and treat any low. The team may still go ahead, delay the operation or put him on a drip. Telling them early is what matters.
Who decides my insulin plan, the surgeon or my diabetes doctor?
Usually the anaesthetist sets the plan at the pre-surgery check, sometimes with your diabetes doctor or a physician, especially for pumps or complex regimes. If you are given two different instructions, ask them to agree one plan before the day.
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Dr. C. Raghavendra Reddy
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Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
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Sources
- NICE — Perioperative care in adults (NG180)
- NHS — Type 1 diabetes
- Cancer Research UK — Surgery for cancer
- National Cancer Institute — Surgery to treat cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Metformin and Diabetes Tablets Around SurgeryIf you take tablets as well as insulinWhich Medicines to Stop Before Cancer SurgeryThe full list your team will go throughWhen Do You Restart Your Regular Medicines?Getting back to your usual routineAnaesthesia for Cancer SurgeryThe pre-anaesthetic check where your plan is set
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