High Blood Sugar With COVID-19 | What To Watch And Do

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Illness stress and some treatments can push glucose up during infection; check often and act early on rising numbers.

Getting sick can send blood sugar off track, even when you’ve had steady numbers for months. COVID-19 is no exception. Fever, lower appetite, less movement, dehydration, and stress hormones can all nudge glucose upward. Some people also receive steroid treatment, which can raise glucose fast.

This article breaks down why spikes happen, what patterns are common, and what actions help most. It also lays out clear “get help now” signals, since severe hyperglycemia can turn into an emergency.

Why Blood Sugar Can Rise During COVID-19

Your body treats an infection like a full-body workout. Stress hormones (like cortisol and adrenaline) rise to keep energy available. One side effect: the liver releases more glucose, and cells may respond less to insulin for a while.

Illness Stress And Inflammation

When you’re fighting a virus, your immune system ramps up. That process can make insulin work less well for a stretch, so glucose stays higher after meals and also between meals. If you already have diabetes or prediabetes, that “resistance” can show up quickly on a meter or CGM.

Dehydration Concentrates Glucose

Fever, sweating, fast breathing, vomiting, and diarrhea all pull fluid out of you. Less fluid in the bloodstream can make glucose readings climb. Dehydration also strains the kidneys, which are part of how the body clears extra glucose.

Less Movement And Sleep Disruption

Even small daily movement helps muscles use glucose. During COVID-19, people often rest more and sleep poorly. That combo can raise fasting numbers and make post-meal spikes sharper.

Steroid Treatment Can Push Numbers Up Fast

Some hospitalized patients receive steroids such as dexamethasone. Steroids can raise glucose and can reveal diabetes that was already brewing. Research and clinical reports during the pandemic have repeatedly noted steroid-associated hyperglycemia in COVID-19 care.

High Blood Sugar With COVID-19: What Triggers The Spike

Not every infection day looks the same. Many people see a pattern: higher fasting glucose in the morning, bigger rises after meals, then slow improvement as fever and inflammation settle. Others see the opposite at first—lower appetite, lower food intake, and glucose dips—followed by a rebound spike once eating returns or medications change.

What counts most is spotting the direction early. A steady drift upward across several checks is a stronger signal than one odd reading.

Who Tends To See Bigger Swings

  • People with type 1 or type 2 diabetes
  • People with prediabetes or past gestational diabetes
  • People taking steroids for COVID-19 or other conditions
  • People who are older or have other chronic conditions that raise the odds of severe illness

If you’re in a higher-risk group, it’s worth treating glucose checks like a routine vital sign during illness. The CDC lists diabetes among conditions linked with higher odds of severe COVID-19 illness. CDC COVID-19 risk factors

What To Do First When You Notice Rising Glucose

Think in three lanes: measure, fluids, and carbs/meds. Small moves early can prevent a runaway rise later.

Measure More Often For A Short Window

If you use a meter, check more often than your usual routine until numbers settle. If you use a CGM, watch trend arrows and time-in-range rather than chasing single points. Write down:

  • Time and reading
  • Food and drink
  • Fever, vomiting, diarrhea, or fast breathing
  • Any new meds, especially steroids

Prioritize Fluids Early

Start with frequent sips, even if you don’t feel thirsty. Water is a solid default. If you’re not eating much, add fluids that bring some carbs and electrolytes so you don’t crash low and then rebound high. If you have kidney disease, heart failure, or a fluid limit, follow the plan you already have from your clinician.

Keep Carbs Steady When You Can Eat

During illness, extreme swings in carbs can create extreme swings in glucose. If you can tolerate food, aim for smaller, steadier meals. If you can’t, shift to easier options like soup, yogurt, or toast—foods you can keep down. Pair carbs with protein when possible to blunt spikes.

Do Not Stop Insulin Just Because You’re Not Eating

For people with type 1 diabetes, insulin is still needed during illness even when intake is low. Skipping insulin can raise ketones and lead to diabetic ketoacidosis (DKA). If you’re unsure what to adjust, call your diabetes care team for a sick-day plan that fits your regimen.

The American Diabetes Association’s sick-day guidance spells out a clear approach, including how often to check glucose and ketones. ADA sick day planning

What Numbers Mean During Illness

Your target range depends on your personal plan, age, pregnancy status, and other factors. Still, illness has a few red-flag patterns that should prompt action. Two general rules help:

  • A rising trend that does not respond to your usual correction strategy calls for closer monitoring.
  • High glucose plus dehydration symptoms or ketones calls for urgent guidance.

Unit note: Many countries use mmol/L. A quick conversion: 10 mmol/L is about 180 mg/dL; 13.9 mmol/L is about 250 mg/dL; 16.7 mmol/L is about 300 mg/dL.

Ketones Change The Whole Picture

If you have type 1 diabetes, or you take an SGLT2 inhibitor, ketone checks during illness can be a lifesaver. Ketones can rise when insulin is not sufficient for the body’s needs. That can happen even if glucose is not sky-high.

The ADA advises ketone testing every 4 to 6 hours when sick for people at risk, and also when glucose is high. ADA guidance on ketones and DKA

Common Drivers And Practical Fixes

Use the table below as a quick way to match a likely driver with a next step. This is not a replacement for your personal plan, but it can help you spot what’s pushing your readings.

Driver During COVID-19 What You Might Notice What To Do Next
Fever and infection stress Higher fasting and between-meal readings Check more often; hydrate; use your correction plan if prescribed
Dehydration Dry mouth, dark urine, dizziness, rising glucose Frequent sips; oral rehydration if tolerated; seek care if you can’t keep fluids down
Reduced appetite Lower intake, then rebound highs later Small, steady carbs; avoid skipping basal insulin without a clinician’s plan
Vomiting or diarrhea Hard to eat and drink; weakness Focus on fluids and carbs in small doses; check ketones if at risk
Steroids (such as dexamethasone) Sharp rise after meals; higher numbers through the day Tell your care team you’re on steroids; insulin or med changes may be needed
Less movement Higher post-meal spikes If safe, add light movement in short bouts; stop if dizzy or short of breath
Poor sleep Higher morning glucose Keep a simple bedtime routine; manage fever and pain per your plan
Over-treating lows Low, then big spike Use measured carbs for lows; recheck; avoid “panic snacking”
Missed doses or supply gaps Unexpected highs that persist Fix the gap fast; ask pharmacy or clinic for bridge options

Medication Notes During COVID-19

Medication choices depend on your diagnosis, kidney function, and how sick you feel. The safest move is to follow a sick-day plan you already have. If you don’t have one, call your clinician’s office early in the illness rather than waiting for a crisis.

Insulin Users

Illness often raises insulin needs. If you use rapid-acting insulin for corrections, follow your prescribed correction factor and timing rules. If you use a pump, watch for infusion set issues, since a kinked cannula can mimic “mystery highs.”

Oral And Non-Insulin Injectables

Some meds can be harder to manage during dehydration or reduced intake. If you’re vomiting, have diarrhea, or can’t keep fluids down, call your care team to review what to pause and what to keep going. Bring your latest glucose log and a list of meds to that call.

Steroids In Hospital Or After Discharge

If you receive steroids, ask how long the course lasts and what glucose plan the team expects you to use at home. Steroid-related rises often show up more after meals and later in the day. Adjustments may be temporary, but they should be planned, not guessed.

When High Blood Sugar Turns Into An Emergency

COVID-19 can start as a respiratory illness and still end up as a glucose emergency if dehydration and insulin shortage stack up. Learn the danger signals so you can act fast.

NIDDK notes that very high blood glucose can become a medical emergency, with symptoms like confusion or fainting in severe cases. NIDDK on managing diabetes and high glucose

Situation What It Can Signal Action Now
Persistent high glucose that keeps rising Illness-driven insulin resistance or missed insulin Increase monitoring; follow correction plan; call clinician if it won’t come down
Moderate to large ketones DKA risk Use your ketone protocol; contact urgent care guidance right away
Fast breathing, belly pain, vomiting Possible DKA Seek emergency care
Extreme thirst, dry mouth, little urination Dehydration with worsening hyperglycemia Start fluids; seek care if you can’t rehydrate
Confusion, fainting, severe weakness Severe hyperglycemia or other acute issue Emergency care
Fever that won’t break plus rising glucose Ongoing infection stress Call clinician; review meds, hydration, and glucose plan
Low oxygen symptoms with high glucose Severe COVID-19 stress on the body Urgent evaluation
Repeated lows followed by rebounds Mismatch between intake and meds Use measured carb treatment; discuss med timing with clinician

Simple Sick-Day Routine You Can Stick With

When you’re tired and congested, complex plans fall apart. A short routine works better. Try this structure for the first few days of illness:

Morning

  • Check glucose soon after waking.
  • Drink a glass of water or an electrolyte drink if you’ve had sweating, diarrhea, or fever.
  • Eat a small breakfast if you can tolerate it.

Midday

  • Recheck glucose and watch the trend.
  • If you use insulin, follow your meal and correction plan.
  • If you’re not eating, keep sipping fluids and take carbs in small doses if you trend low.

Evening

  • Check glucose before dinner and before sleep.
  • If you’re at risk for ketones, test ketones based on your sick-day plan.
  • Set supplies within reach: meter/strips, glucose tabs, ketone strips, thermometer, fluids.

If you’re using a CGM, confirm unusual readings with a fingerstick when symptoms don’t match the sensor, or when the device prompts for confirmation.

After COVID-19: What To Watch In The Next Few Weeks

Many people see glucose settle as symptoms fade. Still, a subset notice higher fasting numbers or a higher average for weeks. That can happen after any infection, not only COVID-19.

Track Patterns, Not Single Readings

Look at weekly trends: morning readings, after-meal peaks, and overnight stability. If your average is climbing, or you’re using more corrections than usual, bring that log to your next appointment.

Consider A Follow-Up Diabetes Screen If You’ve Never Had One

If you had repeated highs during COVID-19 and no past diabetes diagnosis, ask about a follow-up A1C or fasting glucose test after recovery. NIDDK lists classic diabetes symptoms like increased thirst and urination; those can overlap with illness, so lab work is a cleaner check once you’re well again. NIDDK symptoms and causes overview

Rebuild Basics Gradually

As energy returns, restart movement in small chunks. Reset meal timing. Get sleep back on track. Those basics often pull glucose back toward your usual range without dramatic changes.

If you had severe hyperglycemia in the hospital, ask for a clear discharge plan: what numbers should trigger a call, what med changes are temporary, and when labs should be rechecked.

References & Sources

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