Symptoms
High blood sugar: symptoms, what to do and when it is an emergency
Is this an emergency?
This is not an emergency service. Call 911 or go to the nearest emergency room if you have:
- Blood sugar that stays at 300 mg/dL or above
- High urine ketones, or fruity-smelling breath
- Vomiting that stops you keeping food or fluids down
- Fast, deep breathing or shortness of breath
- Confusion or unusual drowsiness
- A child with strong thirst and frequent urination who is also vomiting, breathing fast or very drowsy
Help lines
High blood sugar (hyperglycemia) is when the glucose in your blood rises above normal. It causes thirst, frequent urination, blurry vision and tiredness. It can come from diabetes you didn’t know you had, poorly controlled diabetes, an infection or stress. If your sugar stays at 300 or above with vomiting or fast breathing, go to the ER.
Other names: Hyperglycemia, High glucose
Possible causes
Undiagnosed or poorly controlled type 2 diabetes
Thirst, frequent urination, tiredness; sometimes no symptoms
Prediabetes
Fasting glucose of 100 to 125 mg/dL; rarely causes symptoms
A missed dose or running out of medicine
Sugar rises when insulin or diabetes medicine is missing
An infection or illness
Being sick raises blood sugar, for example with a UTI or the flu
Type 1 diabetes, especially in children
Symptoms can appear suddenly, over a few weeks
Stress or eating more than usual
The CDC lists both among common causes
On this page(7)
What is high blood sugar?
In Puerto Rico people say "el azúcar" for blood glucose. High blood sugar, or hyperglycemia, happens when the body makes too little insulin or doesn’t respond well to it, so glucose stays in the blood instead of getting into the cells.
For reference, according to the NIH, a fasting glucose of 99 mg/dL or below is normal, 100 to 125 mg/dL is prediabetes, and 126 mg/dL or above is diabetes; a glucose of 200 mg/dL or above at any time, with symptoms, also points to diabetes. For people who already have diabetes, the CDC gives a typical target of 80 to 130 mg/dL before meals and under 180 mg/dL two hours after. Your own target is set by your doctor.
Puerto Rico has the highest rate of diagnosed adult diabetes of any U.S. state or territory: 14.4% in 2021, according to the CDC.
How we help by video with high blood sugar
You see Dr. Diana Nieves Castro, a Puerto Rico-licensed general practice physician with several years of emergency-department experience, in English or Spanish. She asks about your glucose readings, how long they have been high, your symptoms, whether you are sick or have an infection, and which medicines or insulin you use and how you are taking them.
We evaluate, diagnose and treat. If needed, we give you a lab order for a lab near you: glucose, hemoglobin A1c, urine and other tests. If appropriate, the doctor prescribes or adjusts your treatment and we send your prescription to your pharmacy. If you ran out of insulin or your diabetes medicine, a refill is a US$49 follow-up visit on prescription refills.
For long-term control, see type 2 diabetes and chronic care by telehealth. A doctor visit costs US$79, the same price for every age. Request a visit online 24/7 — we confirm your time by email or text.
Your doctor
Dr. Diana Nieves Castro, MD
General practice physician
Several years of emergency-department experience.
Founding Executive Director of The Health Initiative.
High blood sugar symptoms
According to MedlinePlus and the CDC, the most common signs are:
- Being very thirsty or having a dry mouth
- Needing to urinate often
- Blurry vision
- Tiredness or weakness
- Dry skin
- Hunger and losing weight without trying
- Sores that heal slowly or infections that keep coming back
What to do if your blood sugar is high
If you have diabetes and your sugar reads high, check whether you missed a dose, ate more than usual, are sick or under a lot of stress: the CDC lists those causes. Drink water, follow the plan your doctor gave you and check again.
Ketones. The CDC recommends testing your urine for ketones when your blood sugar is 250 mg/dL or above. MedlinePlus advises testing if your sugar has been above your goal for no clear reason for 6 hours with type 1 diabetes, or for 3 days with type 2. If ketones are present, get medical care right away.
If you have never been told you have diabetes and you have these symptoms, don’t wait: the doctor evaluates you and gives you the lab order for testing. See also prediabetes.
High blood sugar in children
In children, type 1 diabetes can appear suddenly, over a few weeks, with strong thirst, frequent urination, new bedwetting, hunger, weight loss, tiredness, nausea, vomiting or belly pain. A child with these symptoms needs to be seen the same day. If they are also vomiting, breathing fast or very drowsy, take them to the ER. If the patient is under 21, a parent or legal guardian stays on camera for the whole visit and shows ID.
When high blood sugar is an emergency
Very high blood sugar can cause diabetic ketoacidosis or hyperosmolar syndrome, which are life-threatening. According to the CDC, call 911 or go to the emergency room right away if:
- Your blood sugar stays at 300 mg/dL or above
- You have high ketones in your urine
- Your breath smells fruity
- You are vomiting and can’t keep food or drinks down
- You are breathing fast and deep, or are short of breath
- You are confused or very drowsy
Frequently asked questions
What counts as high blood sugar?
What should I do if my blood sugar is 300?
Can I get an insulin refill by video?
Does high blood sugar always mean diabetes?
About this page
Author: The Health Initiative
Medical care provided by Dr. Diana Nieves Castro, MD (PR license 24027)
Disclosure: Founding Executive Director of The Health Initiative
Published: 2026-10-02 · Updated: 2026-10-02
Sources (7)
- High blood sugar: self-care (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- Diabetic Ketoacidosis (CDC) (opens in a new tab) (accessed 2026-10-02)
- Manage Blood Sugar (CDC) (opens in a new tab) (accessed 2026-10-02)
- Diabetes Symptoms (CDC) (opens in a new tab) (accessed 2026-10-02)
- Diabetes Tests & Diagnosis (NIDDK, NIH) (opens in a new tab) (accessed 2026-10-02)
- Diabetic hyperglycemic hyperosmolar syndrome (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- Diagnosed diabetes by state and territory, 2021 (CDC, Preventing Chronic Disease) (opens in a new tab) (accessed 2026-10-02)