Can Infection Raise Blood Sugar Levels? | Stress & Glucose

Yes, an infection can raise blood sugar. Stress hormones the body releases to fight illness temporarily increase glucose.

You feel a cold coming on—achy, congested, run down. Then your glucose meter shows a number that doesn’t match what you ate. The spike isn’t random; your immune system is driving it.

Infection triggers a stress response that can raise blood sugar, even in people without diabetes. Understanding this connection helps you manage sick days more effectively and recognize when a high reading needs attention.

The Biological Link Between Infection and Glucose

When your body detects an infection, it launches an immune response. That process involves releasing stress hormones—cortisol, adrenaline, glucagon, and others—that prepare your body to fight the invader.

These hormones signal the liver to release stored glucose into the bloodstream. The CDC explains that the immune system raises blood sugar temporarily as part of this defense mechanism. The effect is a natural stress reaction, not a sign you did anything wrong.

In animal models, some viral infections led to lasting changes in blood glucose regulation, though human evidence is less clear. Researchers are still studying whether infections may contribute to triggering type 2 diabetes over time.

Why Your Body Spikes Glucose During Illness

It may seem counterproductive for your body to raise blood sugar when you’re sick—after all, high glucose can feel draining. But from your body’s perspective, the spike is purposeful. Several mechanisms explain why it happens, and some of these may surprise you.

• Counter-regulatory hormone release: Infection triggers glucagon, cortisol, and catecholamines, all of which push glucose out of the liver and into the bloodstream for quick energy.
• Insulin resistance increases temporarily: Stress hormones make your cells less responsive to insulin, so glucose stays in the blood longer. This is temporary and typically reverses as you recover.
• Dehydration from fever or reduced intake: When you’re sick, you may drink less or lose fluid through sweating. Higher blood concentration can elevate glucose readings, even if actual blood sugar hasn’t changed.
• Reduced medication effectiveness: Illness can change how quickly your body absorbs or processes diabetes medications, making it harder to keep blood sugar in range.
• Inactivity and altered eating patterns: Resting more and eating less (or differently) during illness can also shift glucose levels up or down, adding variability.

The combination of hormonal, behavioral, and medication-related factors means blood sugar can swing unpredictably during any infection—even a mild one.

How High Can Blood Sugar Go?

The degree of increase depends on the severity of the infection, your baseline health, and whether you have diabetes. In people with diabetes, spikes can be significant—sometimes into ranges that require medical attention.

Cleveland Clinic notes that hyperglycemia occurs when there’s too much sugar in the blood, and illness is among the common triggers. See its hyperglycemia high blood sugar resource for more detail on how infection fits into the bigger picture.

For someone without diabetes, the spike is usually modest and temporary—often staying within a range that resolves on its own after recovery. Lab reference ranges vary, but a fasting level below 100 mg/dL (5.6 mmol/L) is considered normal; levels between 100 and 125 mg/dL may indicate prediabetes.

Condition	Fasting Blood Sugar Range	Typical Response to Infection
No diabetes	Below 100 mg/dL	May rise 10–30 mg/dL; returns to normal after recovery
Prediabetes	100–125 mg/dL	May rise 20–50 mg/dL; could push into hyperglycemic range
Type 2 diabetes	Above 125 mg/dL (diagnostic)	Can spike 50–100+ mg/dL; medication adjustments often needed
Type 1 diabetes	Above 125 mg/dL (diagnostic)	Rapid spikes possible; risk of diabetic ketoacidosis increases
Stress hyperglycemia (no diabetes)	Normal at baseline	Temporary rise during illness; typically resolves within days

These ranges are broad guidelines. Individual responses vary, so taking a trend across several readings gives a clearer picture than any single number.

Infections Most Likely to Raise Blood Sugar

Any infection that triggers a significant immune response can raise blood sugar, but some are more commonly associated with large spikes. Knowing which illnesses pose higher risk helps you prepare.

1. Flu and respiratory infections: Influenza, COVID-19, and pneumonia are among the most common culprits. They provoke a strong stress hormone response and can cause sustained high glucose for days.
2. Urinary tract infections (UTIs): UTIs are bacterial infections that trigger the same stress hormone cascade. In people with diabetes, UTIs tend to be more frequent and harder to clear, compounding the glucose effect.
3. Skin and soft tissue infections: Even a small infected wound or cellulitis can raise blood sugar, especially if diabetes is already present. The infection and high glucose can create a cycle where each worsens the other.
4. Gastrointestinal infections: Stomach bugs cause vomiting, diarrhea, and dehydration, which can push blood sugar in either direction—up due to stress hormones or down due to poor absorption of food and meds.
5. Post-surgical infections: Hospital-related hyperglycemia is well-documented. Surgery stress plus infection can drive glucose high, which is why surgical teams monitor blood sugar closely during recovery.

If you have diabetes, even a minor infection warrants extra attention. Checking blood sugar every four to six hours while sick is one way to catch spikes early.

When High Blood Sugar Becomes an Emergency

For most people, infection-related glucose spikes are temporary and manageable. But there’s a line where high blood sugar crosses into dangerous territory, especially for those with type 1 diabetes or severe insulin deficiency.

Diabetic ketoacidosis (DKA) can develop when infection raises blood sugar significantly and insulin levels are too low. Verywell Health outlines the infection and DKA risk in detail, emphasizing that illness can push the body into a state where it breaks down fat too quickly, producing acids called ketones.

Warning signs include blood sugar persistently above 250 mg/dL, fruity-smelling breath, rapid breathing, nausea or vomiting, and confusion. If several of these appear together, seeking medical attention promptly is appropriate.

Blood Sugar Level	Risk Level	Recommended Action
Below 180 mg/dL	Typical sick-day range	Continue monitoring; stay hydrated
180–250 mg/dL	Moderately elevated	Increase fluid intake; check for ketones if diabetic
250–350 mg/dL	High; monitor closely	Check urine or blood ketones; contact your care team
Above 350 mg/dL	Potentially urgent	Seek medical guidance, especially with nausea or confusion

These thresholds are general guidelines. Your provider may set different targets based on your medical history and current medications.

The Bottom Line

Infection can absolutely raise blood sugar, driven by stress hormones that release stored glucose and temporarily reduce insulin sensitivity. The effect is natural and usually reversible, but it requires extra attention for people with diabetes. Monitoring more frequently, staying hydrated, and knowing emergency warning signs make a real difference during sick days.

If you have diabetes and notice blood sugar climbing during an infection, your primary care doctor or endocrinologist can help adjust medications or recommend sick-day protocols tailored to your usual glucose trends.