Understanding High Blood Sugar: A Comprehensive Guide

A caregiver-focused guide to high blood sugar signs, safe next steps, emergency warnings, and a subscriber-only printable fact sheet.

High blood sugar, also called hyperglycemia, means the glucose level in the blood is above the person’s target range. Targets and response steps are individual, so caregivers should use the written diabetes plan from the person’s health care team rather than changing insulin, medicine, food, or activity on their own.

Common signs of high blood sugar

The American Diabetes Association’s hyperglycemia guidance lists frequent urination and increased thirst among common signs. Other symptoms can occur, and symptoms alone cannot show how high the glucose level is. When the person’s care plan calls for it, check with their glucose meter or continuous glucose monitor and compare the result with their personal target range.

What caregivers can do

  1. Check the written care plan. Follow the person-specific instructions for glucose checks, ketone testing, medicines, fluids, meals, and when to contact the diabetes care team.
  2. Confirm medicines were taken as prescribed. Do not give extra insulin or change a dose unless the person’s clinician has provided an individualized correction plan.
  3. Record what is happening. Note the glucose reading, symptoms, ketone result if tested, medicines taken, illness, food, and the time. This can help the care team give safer advice.
  4. Recheck and call as directed. Contact the diabetes care team when readings remain above the person’s target, symptoms are worsening, the plan says to call, or you are unsure what to do.

The ADA advises checking urine for ketones when blood glucose is above 240 mg/dL and not exercising if ketones are present, because exercise may raise glucose further. Use the person’s own clinician-approved plan for testing and activity decisions.

When high blood sugar is an emergency

Diabetic ketoacidosis (DKA) is serious and can be life-threatening. The CDC’s current DKA guidance says to call 911 or go to an emergency room right away when ketones are high, blood sugar stays at 300 mg/dL or above, breath smells fruity, the person is vomiting and cannot keep food or drinks down, the person is having trouble breathing, or several DKA signs occur together.

Do not wait for every sign to appear. If the person is unconscious, having trouble breathing, or cannot be kept safe, call 911.

What the subscriber fact sheet includes

The three-page printable Diabetes and High Blood Sugar fact sheet summarizes early and later warning signs, common causes, prevention topics, ketone testing, and a short response checklist. It is available to subscribers through the sign-up or sign-in option below. The download supports—but does not replace—the person’s current diabetes plan or medical advice.

High and low glucose require different responses. Review the signs of low blood sugar, prepare for appointments with these questions to ask about medications, and use the medication safety and storage guide.

Source review: August 11, 2026. This educational overview was checked against the CDC and American Diabetes Association pages linked above. It does not replace diagnosis, treatment, or an individualized emergency plan from a licensed health professional.