high sugar with fever
Informed by recognized medical guidance
Overview
When you have a fever, your body releases extra stress hormones. These hormones can cause your blood sugar (glucose) to rise, even if you don’t usually have diabetes. For people with diabetes, a fever can make blood sugar harder to control. This is sometimes called sick-day hyperglycemia.
Key facts
- Fever and infection can make blood sugar levels rise quickly.
- Drinking plenty of fluids and checking blood sugar often are key.
- People with diabetes should have a sick-day plan ready.
It is common for blood sugar levels to go up during any illness, especially when there is a fever. Most people with diabetes will experience this at some point.
It most often affects people who already have diabetes, but it can also happen in people without diabetes who have a severe infection or critical illness.
Symptoms
- Severe drowsiness or difficulty waking up
- Fast, deep breathing that doesn’t slow down
- Vomiting that won’t stop
- Very high blood sugar reading you cannot lower
- Signs of dehydration with severe weakness
- ⚠Fever that lasts more than 24 hours
- ⚠Unable to keep fluids down
- ⚠Blood sugar levels much higher than your usual target
- ⚠Signs of infection like pain or pus
Common symptoms
- More thirst than usual
- Urinating more often
- Feeling very tired or weak
- Blurred vision
- Dry mouth and lips
- Headache
Symptoms in children
- Drowsiness or low energy
- Fruity-smelling breath
- Nausea or stomach pain
- Deep, rapid breathing
Symptoms in older adults
- Confusion or trouble thinking
- Dizziness
- Weakness or shakiness
- Worsening of existing confusion
Causes
Main causes
- Fever from infection triggers stress hormones that raise blood sugar.
- Illness can make it harder for the body to use insulin properly.
- Dehydration during illness can push blood sugar higher.
- Being less active while sick can contribute to higher levels.
Risk factors
- Having diabetes (type 1 or type 2)
- Being older or frail
- Having a chronic illness
- Taking steroid medicines
When to see a doctor
See a doctor urgently if:
- Call your healthcare provider today if you have a fever and high blood sugar that does not come down, or if you cannot eat or drink normally.
- Seek urgent care if you have signs of dehydration or vomiting for more than a few hours.
Book a routine appointment if:
- Contact your diabetes care team if your blood sugar stays higher than your target for more than a day after your fever improves.
- Ask your provider about creating a personal sick-day plan before you get ill.
Diagnosis
Doctors diagnose high blood sugar with a simple blood test. If you have diabetes, you may also check your own blood sugar at home. During an illness, you may need to check it more often.
Tests that may be done
- Blood glucose measurement
- Urine test for ketones (acids that can build up)
- Blood tests for electrolytes
- Tests to find the source of infection, such as a urine or chest test
What to expect at your appointment
Your provider will ask about your fever, how much you’re drinking, and your blood sugar readings. They may recommend more checks or a visit to the lab for blood tests.
Treatment
The main goals are to bring the fever down, keep fluid levels healthy, and manage blood sugar. Most care happens at home, but severe cases may need a hospital.
Self-care at home
- Drink water or sugar-free fluids regularly to avoid dehydration.
- Check your blood sugar more often than usual.
- Rest as much as possible.
- Eat light meals or snacks if you can, following your usual meal plan.
- Follow the sick-day advice your care team has given you.
Medical treatments
Your healthcare provider may adjust your usual diabetes medicines temporarily during an illness. They may also prescribe medication to treat the infection causing the fever. In more serious cases, hospital care with fluids and glucose management may be needed.
Living with this condition
When you’re sick, keep a log of your blood sugar readings, temperature, and how much you drink. This will help you and your care team decide if something needs to change.
Lifestyle tips
- Stay up to date on vaccinations to reduce infection risk.
- Wash hands often to prevent illness.
- Have a supply of blood sugar testing strips and fluids available.
Diet and exercise
With a fever, don’t worry about exercising. Focus on rest and drinking fluids. If you have a diabetes meal plan, try to keep your usual eating times even if portions are smaller.
Mental health and emotional wellbeing
Stress, worry, and the strain of managing diabetes can feel heavier during illness. It’s okay to feel overwhelmed. Reach out to someone you trust or your care team if you’re struggling. If you are having thoughts of harming yourself or feel you cannot cope, call your local emergency number or reach out to a crisis line.
Prevention
You cannot always prevent a fever, but you can reduce the risk of infections that cause fever. If you have diabetes, keeping your blood sugar in a good target range before illness helps you recover more smoothly.
Vaccines
Ask your healthcare provider about recommended vaccinations, such as flu and pneumonia vaccines, which can help prevent serious infections.
Complications
If left untreated
- Dehydration and electrolyte imbalances
- Very high blood sugar leading to diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS)
- Worsening infection or sepsis
Long-term outlook
Most people recover well with prompt care. Staying connected with your care team and acting early can prevent serious problems.
Find support
International organisations
Local organisations
- Diabetes UK ↗ · UK
External links open third-party websites. Ruqelo Health is not responsible for external content. Listing an organisation does not imply endorsement.
Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
Related conditions
Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 31, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.