Complications Of Blood Sugar Level Of 455 mg/dl?

Answer by Dr. Albana Greca, MD, MMedSc

Hello,

A reading of 455 mg/dL—about 25.3 mmol/L—is severe hyperglycemia. Possible causes include missed or insufficient medicine, infection, dehydration, corticosteroids, insulin-delivery failure, or worsening diabetes.

What Should You Do Right Now?

1. Wash and dry your hands and repeat the test with an in-date strip if this was a home-meter reading.


2. Check blood or urine ketones if you have been instructed to do so or have supplies available.


3. Follow only your prescribed correction or sick-day plan. Do not guess an extra insulin dose.


4. Drink water or sugar-free fluids if safe and not medically restricted.


5. Contact your diabetes clinician or urgent medical service immediately. Same-day assessment is appropriate even if you feel well.

Do not exercise when ketones are present or you feel ill.

Short-Term Complications

Severe dehydration

Very high glucose pulls water into the urine, causing frequent urination, thirst, dry mouth, weakness, dizziness, lower blood pressure, and worsening kidney function.

Diabetic ketoacidosis

DKA occurs when insufficient insulin allows ketones and acid to build up. It is more common in type 1 diabetes but can occur in type 2 diabetes, especially with infection, severe illness, insulin deficiency, or SGLT2-inhibitor use.

Symptoms include nausea, vomiting, abdominal pain, rapid or deep breathing, fruity breath, severe weakness, dehydration, drowsiness, and confusion. Diagnosis requires ketone, acid-base, and electrolyte testing.

Hyperglycemic hyperosmolar state

HHS involves severe hyperglycemia, profound dehydration, high osmolality, and mental-status changes. It is more common in older adults with type 2 diabetes.

A glucose of 455 mg/dL does not prove HHS, which often involves even higher levels, but it may already be accompanied by dangerous dehydration, electrolyte disturbance, or kidney injury.

Electrolyte and circulation problems

Severe hyperglycemia can disturb electrolytes and affect the heart, brain, muscles, and kidneys. Treatment may require monitored fluids, insulin, and electrolyte replacement.

Does One Reading of 455 Cause Long-Term Complications?

One episode does not automatically cause blindness, kidney failure, neuropathy, heart attack, or stroke. Long-term complications relate mainly to sustained hyperglycemia and other risk factors.

Repeated or sustained hyperglycemia can increase the risk of:

• eye disease: retinopathy, macular edema, and vision loss;


• kidney disease: albuminuria and declining kidney function;


• nerve damage: pain, numbness, autonomic problems, and loss of foot sensation;


• foot complications: ulcers, infection, poor healing, and amputation risk;


• cardiovascular disease: heart attack, stroke, and peripheral arterial disease;


• infection and poor healing.

These outcomes are not inevitable. Safer glucose, blood-pressure and cholesterol control, screening, foot care, avoiding tobacco, and appropriate medicines reduce risk. See our diabetes complications guide.

What May Be Causing the Reading?

• missed, delayed, expired, or insufficient insulin or medicine;


• infection, fever, surgery, injury, or another acute illness;


• corticosteroids or another glucose-raising medicine;


• insulin pump, infusion-set, pen, or injection problem;


• dehydration;


• very high carbohydrate intake;


• newly diagnosed or worsening diabetes.

Your team may check ketones, electrolytes, kidney function, acid-base status, infection, and HbA1c, then review treatment and sick-day instructions.

What Not to Do

• Do not wait several days to see whether 455 mg/dL improves.


• Do not take an unplanned large insulin dose.


• Do not stop basal insulin because you are not eating.


• Do not exercise when ketones are present or you feel unwell.


• Do not rely on herbs, vinegar, supplements, or water alone.


• Do not drive yourself if you are confused, very weak, faint, or severely dehydrated.

Educational safety note: This answer is general education and cannot assess your condition or calculate insulin. Follow your personal emergency plan and seek urgent medical care.

Related Questions

• What Should I Do About Blood Sugar of 397 mg/dL?


• Why Is Blood Sugar Still Very High While Taking Insulin?


• What Causes Blood Sugar to Stay as High as 306 mg/dL?

Related Resources

• Dangerous Blood Sugar Levels


• Blood Sugar Over 400 mg/dL


• Blood Sugar From 250 to 400 mg/dL


• Diabetes Complications and Prevention

Last reviewed: July 2026