Can Infection Raise Blood Sugar Levels in Non-Diabetics?

Yes, an infection can raise blood sugar in non-diabetics as the body’s immune response releases stress hormones that temporarily increase glucose.

Most people think of blood sugar spikes as something that happens only after eating too many carbs or if you have diabetes. But a fever, a urinary tract infection, or even a bad cold can send your glucose levels climbing — even if you have never had a prediabetes diagnosis.

The short answer is yes, an infection can raise blood sugar in people without diabetes. It’s a normal part of the body’s immune response, driven by stress hormones like cortisol. This article explains how that happens, which infections pose the biggest risk, and when to talk to a doctor about temporary hyperglycemia.

How Infection Triggers a Blood Sugar Spike

When your body detects an infection, your immune system kicks into gear. One of its first moves is releasing stress hormones — especially cortisol. These hormones signal your liver to release stored glucose into the bloodstream. The extra sugar gives your cells quick energy to fight the invader.

The CDC notes that the immune system releases hormones that can temporarily increase blood sugar as part of the healing process. Similarly, Mayo Clinic lists illness, infection, injury, and surgery as common causes of blood sugar fluctuation. UnityPoint Health adds that excess cortisol is a key driver of infection-related glucose rises.

This type of temporary high blood sugar is sometimes called “stress hyperglycemia.” In non-diabetics, it typically resolves once the infection clears and hormone levels return to normal. The rise is usually modest — often not enough to cause symptoms on its own — but can be more noticeable during severe illness or in people with underlying insulin resistance.

Why Many People Are Surprised by the Link

It’s easy to assume high blood sugar is only a concern for diabetics or after heavy meals. But the body’s response to infection doesn’t check your fasting glucose level first. Several reasons the infection–glucose connection catches people off guard:

• Glucose only from food assumption: Many people believe blood sugar changes only come from what you eat. They don’t realize the liver can produce glucose on demand when stress hormones ramp up.
• Illness and glucose aren’t obvious partners: Colds, UTIs, and the flu seem like totally separate systems from metabolism. The link between immune and endocrine responses isn’t common knowledge.
• Stress hormones are invisible: You can feel a fever or body aches, but the cortisol surge operates silently. Without a glucose monitor, you might never know your sugar is temporarily elevated.
• Overlapping symptoms: Increased thirst, frequent urination, and fatigue are classic hyperglycemia signs — but they are also common during any infection. It’s easy to write them off as part of being sick.
• No routine monitoring during illness: Most non-diabetics don’t own a glucose meter. Unless a doctor orders lab work, a transient spike goes unnoticed.

The key point is that a temporary spike during a cold or flu is typically normal and resolves as you recover. But if it persists or you have other risk factors, it’s worth monitoring.

When Blood Sugar Rises Without Diabetes: Infections to Know

Not every infection raises blood sugar equally. The severity of the immune response matters. Per the Cleveland Clinic’s definition of hyperglycemia, the condition involves excess glucose in the blood. But when infection triggers that rise, the mechanism is different from dietary spikes.

Serious infections like sepsis are associated with higher glucose levels. A peer-reviewed study found blood glucose in sepsis patients is positively correlated with inflammatory markers — the more inflammation, the higher the sugar. Urinary tract infections (UTIs) also show this connection: one study found that admission hyperglycemia raises the risk of developing a UTI in hospitalized patients. Viral infections like the flu can also trigger a cortisol-driven rise.

For non-diabetics, even a moderate rise — say, from a normal 90–100 mg/dL to 130–150 mg/dL — is generally temporary. However, people with undiagnosed prediabetes (A1C between 5.7% and 6.4%) may experience a more pronounced or prolonged response. If you suspect you fall into that range, an infection can be a revealing event.

Type of Infection	Mechanism	Typical Effect for Non-Diabetics
Sepsis	Widespread inflammation and high cortisol	Can cause moderate to significant temporary rise
Urinary tract infection (UTI)	Localized inflammation, stress hormone release	May raise blood sugar, especially if untreated
Influenza (flu)	Viral immune response, fever	Often produces a mild, short-lived spike
Pneumonia	Lung infection with systemic stress	Can elevate glucose; more pronounced in severe cases
Post-surgical infection	Combined surgical trauma and immune response	Temporary rise is common; usually resolves with recovery

These connections are well supported by clinical research. Even mild infections can nudge your glucose upward, though the effect is usually too small to notice without testing.

Signs Your Blood Sugar May Be Elevated During an Illness

If you don’t typically monitor your glucose, you might not notice changes during an infection. But some symptoms can hint at elevated blood sugar along with the usual sick-day feelings. Look for these markers:

1. Increased thirst and dry mouth: Feeling extra thirsty even though you’re drinking plenty of fluids can indicate higher glucose levels pulling water from your tissues.
2. Frequent urination: Needing to urinate more often than expected from fever-induced dehydration alone may signal that your kidneys are flushing out excess sugar.
3. Fatigue beyond normal illness: While fatigue is expected with any infection, a deeper tiredness that doesn’t match your fever or activity level can be a clue.
4. Blurred vision: Rapid glucose changes can affect the lens of your eye, causing temporary blurriness that improves once sugar normalizes.
5. Slower healing of cuts or sores: If you have a wound, elevated glucose can slow tissue repair. This is more common with prolonged or severe hyperglycemia.

These symptoms overlap with both hyperglycemia and infection itself, so they’re easy to overlook. If you have a home glucose meter, testing during illness can give you a clearer picture. A fasting level above 126 mg/dL or a random level above 200 mg/dL is worth following up with your doctor.

What to Do About Elevated Blood Sugar During an Infection

For most non-diabetics, a temporary glucose rise during illness doesn’t require treatment beyond managing the infection itself. Staying hydrated, getting rest, and eating balanced meals help your immune system work efficiently. Avoid sugary drinks that could add a dietary spike on top of the stress-related rise.

Blood sugar during illness typically normalizes after recovery — the Mayo Clinic explains the connection in its illness infection injury surgery overview. Some cold and flu medicines contain sugars or ingredients (like decongestants) that can further affect glucose, so check labels or ask a pharmacist if you’re concerned.

When should you call a doctor? If your blood sugar remains elevated a week after your symptoms resolve, or if you experience very high readings (over 250 mg/dL) during illness, it’s worth discussing. People with a family history of diabetes or past prediabetes may want to take extra care. A simple A1C test can help determine whether the infection unmasked a deeper metabolic issue.

Non-Dietary Trigger	How It Can Raise Blood Sugar
Illness or infection	Immune system releases cortisol, increasing liver glucose output
Severe emotional stress	Similar cortisol-driven glucose release
Certain medications (e.g., decongestants, steroids)	May interfere with insulin or glucose metabolism

The Bottom Line

Infection can temporarily raise blood sugar in non-diabetics due to stress hormones released during the immune response. This stress hyperglycemia is usually mild and resolves on its own. Severe infections like sepsis or UTIs may cause more significant spikes, but for most people, a brief elevation during a cold or flu is nothing to worry about.

If you notice persistent high readings on a home meter a week after your symptoms resolve, your primary care doctor can check your A1C to rule out underlying prediabetes or diabetes — a simple blood test that gives a clear picture of your average glucose over the past few months.