Can An Infection Cause High Blood Sugars? | Spikes Explained

Yes—illness can push glucose up by raising stress hormones and insulin resistance, even if you eat less than usual.

If your readings jump when you’re sick, you’re not alone. Colds, flu, stomach bugs, urinary tract infections, skin infections, and dental infections can all nudge glucose higher. Sometimes the rise is mild. Sometimes it’s a stubborn climb that doesn’t match what you ate.

Below you’ll get the “why,” the clues that point to infection, and a simple sick-day plan you can use the same day you notice the spike.

Why Infections Can Raise Blood Sugar

Your body treats infection like an emergency drill. To fuel immune cells, it releases counter-regulatory hormones such as cortisol and adrenaline. Those hormones tell the liver to release stored glucose and to make new glucose. They also make muscle and fat cells less responsive to insulin.

The American Diabetes Association’s sick-day guidance explains that illness can trigger hormone release that raises blood glucose and makes it harder to stay in range.

Inflammation can add to the problem. When your immune system ramps up, insulin resistance can rise. If you’re dehydrated from fever, vomiting, or diarrhea, glucose can concentrate in the bloodstream and readings can climb even more.

What This Looks Like On A Glucose Meter

Illness-related spikes tend to share a few traits:

• They’re sticky. Glucose stays high across multiple checks, even if meals are smaller.
• They start early. Numbers may rise before you fully feel sick.
• They ignore your usual fixes. Your normal routine may not bring levels down the way it usually does.

Not every spike is an infection. Poor sleep, missed medication, steroid medicines, dehydration, and pain can also raise glucose. The goal is to match the pattern to symptoms and timing.

Can An Infection Cause High Blood Sugars? How The Body Responds

Yes. During infection, your body releases hormones to fight illness, and those same hormones can raise blood sugar. The CDC’s sick-day page notes that this hormone response can make blood sugar hard to manage when you’re sick and that you may need to test more often.

You can see high glucose even when appetite drops. Your liver can still pump out glucose under hormone signals, and cells may not take it up well because insulin isn’t working as efficiently in tissues.

Type 1 Versus Type 2: The Risk Profile Differs

With type 1 diabetes, infection can raise the risk of ketone buildup and diabetic ketoacidosis (DKA), since insulin needs can rise fast while eating may drop. With type 2 diabetes, infection can still drive glucose high, and severe dehydration can raise the risk of a hyperosmolar crisis, especially in older adults.

Clues That Point To Infection

Infections don’t always come with a dramatic fever. Some start quietly. These clues often line up with infection-driven hyperglycemia.

Body Clues

• Fever, chills, or waking up sweaty
• Sore throat, cough, chest tightness, or breathlessness
• Pain or burning with urination, cloudy urine, or urgency
• Red, warm, tender skin areas, or a cut that looks worse day to day
• Tooth pain, swollen gums, bad taste, or jaw tenderness
• Vomiting, diarrhea, or belly pain

Glucose Pattern Clues

• Fasting readings rise for two mornings without a clear food reason
• Corrections work slowly or wear off fast
• Readings run high across the day, not just after meals
• Thirst and more frequent urination

If you have chest pain, confusion, fast breathing, or repeated vomiting, get medical care the same day.

What To Do When You’re Sick And Glucose Runs High

When illness hits, your routine needs a short-term switch. The goal is steady monitoring and simple actions that prevent dehydration and catch ketosis early.

Step 1: Check More Often And Log The Basics

During illness, check glucose more frequently than normal. Many care plans use a 2–4 hour rhythm for a short stretch, then ease back as symptoms improve. Keep a simple log of readings, temperature, fluids, and medicines taken. That timeline helps your clinician make safe adjustments.

Step 2: Keep Fluids Steady

Dehydration can push readings up and can make you feel worse. Sip water, broth, or sugar-free electrolyte drinks. If you can’t keep fluids down, that alone can be a reason for urgent care.

Step 3: Keep Taking Diabetes Medicine Unless Your Plan Says Otherwise

Even if you’re eating less, your body may need the same dose or more. MedlinePlus sick-day instructions notes that insulin may not work as well when you’re sick and blood sugar can run higher even with usual doses.

If you use insulin, follow your correction plan and your clinician’s guidance for temporary dose changes. If you use pills or non-insulin injections, follow your plan and call your clinic if you can’t eat, you’re vomiting, or you’re dehydrated.

Step 4: Check Ketones If You’re In A Risk Group

If you have type 1 diabetes, pregnancy with diabetes, or a history of DKA, ketone testing during illness is often part of the plan. Some type 2 patients also check ketones when glucose stays high with nausea or belly pain.

Seek urgent care if ketones are moderate to large, you can’t keep fluids down, or you feel drowsy or confused.

When To Call A Clinic Versus Go To Urgent Care

It helps to split decisions into two lanes: “call today” and “go now.” Your personal plan may set specific numbers, so treat this as a general safety map.

Call Your Clinic Today If

• Glucose stays high despite corrections you normally use
• You’ve been sick for more than 24 hours and readings are trending up
• You need guidance on dose changes, eating less, or medication holds
• You suspect a urinary, skin, or dental infection

Go To Urgent Care Or The ER If

• Repeated vomiting or you can’t keep fluids down
• Moderate to large ketones, or symptoms that feel like DKA
• Fast breathing, chest pain, severe belly pain, or confusion
• Signs of severe dehydration: dizziness when standing or no urination for many hours

If you’re in Singapore, NUHS sick-day guidance lists practical thresholds and symptom cues, including local mmol/L cutoffs many people use.

Common Infections That Often Spike Glucose

Any infection can raise glucose, but these types show up often when readings stay high without an obvious food trigger.

Respiratory Infections

Colds and flu can raise hormones and disrupt sleep, both of which can raise readings. Seek care fast if breathing is hard or you have chest pain.

Urinary Tract Infections

UTIs can raise glucose even when you don’t feel very sick. Watch for burning, urgency, pelvic pain, cloudy urine, or back pain.

Skin, Foot, And Wound Infections

Redness, warmth, swelling, pus, or increasing pain around a cut can signal infection. If you have foot numbness, check feet daily during illness.

Dental Infections

Tooth and gum infections can quietly drive stubborn highs. A bad taste, swollen gums, or jaw tenderness paired with rising readings is a reason to book a dental visit.

Table: Triggers, Clues, And Next Moves

Use the table to match what you’re seeing to a practical next step.

What You Notice	What It Can Point To	Next Step
Fasting glucose jumps for 2 mornings	Early illness response, poor sleep, dehydration	Hydrate, check more often, watch symptoms
High readings all day, not just after meals	Hormone-driven glucose release	Follow correction plan, log readings and fluids
Thirst and frequent urination	Dehydration from hyperglycemia	Increase fluids; seek care if you can’t drink
Nausea, belly pain, fruity breath	Ketone buildup	Check ketones; urgent care if moderate/large
Burning urination or cloudy urine	Urinary tract infection	Arrange clinic visit for testing and treatment
Red, warm, tender skin area	Skin infection	Mark the area; seek care if it spreads
New steroid medicine started	Medication-related hyperglycemia	Ask clinician about temporary dose changes
Fever plus worsening symptoms	Infection getting worse	Same-day medical review

Eating And Drinking When Appetite Is Off

Illness can wreck your usual meal plan. The goal is simple: keep fluids going, avoid big sugar loads, and match any carbs you eat to your medication plan.

If You Can Eat Normal Meals

• Stick close to your usual balanced meals and timing.
• Favor easy proteins like eggs, yogurt, tofu, or soup.

If You Can’t Eat Much

• Try small bites: crackers, toast, rice porridge, bananas, or plain noodles.
• Use sugar-free fluids and add a small carb source only when your plan calls for it.
• Call your clinic if you’re unsure about insulin or other medication dosing.

Table: Sick-Day Monitoring Checklist

This checklist is designed for a fridge door or phone note. Adjust it to match your personal plan.

Task	How Often During Illness	Notes
Check blood glucose	Every 2–4 hours at first	Ease back once stable
Drink fluids	Small sips through the day	Use oral rehydration with diarrhea
Check temperature	2–3 times per day	Track fever pattern
Check ketones (if needed)	When glucose stays high or nausea appears	Follow your ketone plan
Take diabetes medicine	As prescribed	Ask clinic about medication holds if dehydrated
Log readings and symptoms	Each check	Helps safe dose changes

Preventing Surprise Spikes During Cold And Flu Season

A few habits can reduce the odds of hidden infections and can help you react faster when you do get sick.

• Keep a sick-day kit. Extra test supplies, ketone strips (if you use them), a thermometer, and sugar-free electrolytes.
• Check feet and skin. Look for new redness, warmth, swelling, or drainage.
• Stay on top of dental care. Gum infections can be an easy-to-miss driver of stubborn highs.

The Takeaway

Infection can raise blood sugar through hormone release, inflammation, and dehydration. If you see sticky highs with new symptoms, shift into sick-day mode: check more often, drink fluids, follow your medication plan, and check ketones if you’re in a risk group.

When symptoms feel serious, fluids won’t stay down, or ketones rise, get medical care the same day. Treating the infection often brings glucose back toward your usual range.