--- title: "High blood sugar: symptoms, ketones and the 300 mg/dL line" description: "Thirst, frequent urination, blurry vision: the signs of high blood sugar, the CDC's 250 and 300 mg/dL lines, ketones, and when to go to the ER." canonical: https://glucosebench.com/high-blood-sugar alternate_html: https://glucosebench.com/high-blood-sugar language: en-US last_updated: 2026-09-27 type: guia --- # High blood sugar (hyperglycemia): the signs, and the readings that can't wait 1. [Home](https://glucosebench.com/) 2. [Blood sugar basics](https://glucosebench.com/blood-sugar) 3. High blood sugar (hyperglycemia): the signs, and the readings that can't wait Most high readings are a nudge to look at food, activity, illness or a missed dose. A few are an emergency, and the CDC draws that line with numbers. By **GlucoseBench editorial team**Updated September 27, 2026 ![High blood sugar (hyperglycemia): the signs, and the readings that can't wait](https://glucosebench.com/img/guia-high-blood-sugar-640.webp) Short answer Hyperglycemia means high blood glucose; for most people with diabetes, the NIDDK says blood sugar is too high "when it is above 180 mg/dL." The usual signs are feeling thirsty, feeling tired or weak, headaches, urinating often and blurred vision. If you have diabetes and you're sick or your blood sugar is 250 mg/dL or above, the CDC says to check your blood sugar every 4 to 6 hours and check your urine for ketones. Go to the emergency room or call 911 right away if your blood sugar stays at 300 mg/dL or above, your breath smells fruity, you're vomiting and can't keep food or drinks down, you're having trouble breathing, or you have multiple signs and symptoms of DKA. Supplements have no place in that plan; the CDC's own line is "Take medicines as prescribed, even if you feel fine." ## Readings that change what you do The number thresholds are written for people who already have diabetes and check at home. The CDC's emergency list applies to everyone, diagnosed or not: go to the emergency room or call 911 right away for fruity-smelling breath, vomiting with no way to keep food or drinks down, trouble breathing, a blood sugar that stays at 300 mg/dL or above, or several signs and symptoms of DKA at once. If you've never been diagnosed and see high readings without those signs, see a health care provider to find out why; the CDC notes that DKA is sometimes the first sign of diabetes. Reading What the source says to do Source Above 180 mg/dL, often Talk with your health care team; your meal plan, activity or medicines may need a change NIDDK 250 mg/dL or above, or you're sick Check your blood sugar every 4 to 6 hours and check your urine for ketones CDC Any symptom of DKA "You should also test for ketones if you have any of the symptoms of DKA." CDC Very high blood glucose or DKA symptoms, and ketones come back moderate or high (or you have no ketone test) Check ketones every 4 to 6 hours "when your blood glucose is very high or when you are having these symptoms." If moderate or high, or with no test: "contact your health care provider right away or get emergency medical help" MedlinePlus Stays at 300 mg/dL or above Go to the emergency room or call 911 right away CDC Several signs of DKA, fruity breath, vomiting with nothing staying down, or trouble breathing Go to the emergency room or call 911 right away, with or without a diabetes diagnosis CDC Sources: NIDDK, "Managing Diabetes" (last reviewed October 2023); CDC, "Diabetic Ketoacidosis" (May 15, 2024); MedlinePlus, "Hyperglycemia" (updated May 10, 2024). All read on September 27, 2026. On high ketones, the CDC is shorter still: "Call 911 or go to the emergency room right away." ## What running high feels like ### The everyday signs MedlinePlus lists feeling thirsty, feeling tired or weak, headaches, urinating often and blurred vision. The NIDDK's list is the same idea: tired, thirsty, blurry vision, urinating too often. ### When it stays high "In people with diabetes, long-term hyperglycemia can lead to serious health problems," says MedlinePlus. The NIDDK adds that very high blood glucose "may lead to confusion or fainting." ### Signs of DKA The CDC's early signs of diabetic ketoacidosis are being very thirsty and urinating a lot more than usual. "If untreated, more severe symptoms can appear quickly": fast, deep breathing, dry skin and mouth, a flushed face, fruity-smelling breath, headache, muscle aches, deep tiredness, nausea, vomiting and stomach pain. It can be the first sign of diabetes in someone never diagnosed. ### Often, nothing "Prediabetes and type 2 diabetes often don't have any symptoms," the CDC notes. Feeling fine doesn't tell you your number. ## What pushes blood sugar up MedlinePlus puts it plainly: with diabetes, you can get hyperglycemia "if you eat too much food or the wrong foods, don't take your medicines correctly, or don't get physical activity," and also when you're stressed or sick. For DKA, the CDC puts illness and missed insulin (skipped shots, a clogged pump, the wrong dose) at the top of the list. Without diabetes, it's less common. MedlinePlus names problems with the pancreas or adrenal glands, certain medicines and severe illnesses, and says anyone without diabetes who has the symptoms should see a provider to find the cause. ## What to do with a high reading 1. ### Write it down The NIDDK asks you to record the date and time, the result, and what you ate or did that day, and to bring it to your health care team. 2. ### Look for the reason Too much food, less activity, a missed or wrong dose, stress, an illness. Those are the causes MedlinePlus and the CDC name. 3. ### If you are sick, check more often The CDC: "Check your blood sugar often, especially if you're sick." At 250 mg/dL or above, that means every 4 to 6 hours, plus a ketone check. 4. ### Tell your team if it keeps happening "Talk with your health care team if you often have high blood glucose levels," says the NIDDK. The fix may be a change in your meal plan, activity or medicines, and that change is theirs to make with you. ## Sales pages vs. public health advice Four products reviewed on this site are sold with lines that point the opposite way from the CDC and the NIH. We don't recommend any of them. What the sales page says Product What the official source says "You cannot control diabetes with medications or insulin." Blood Sugar Blaster CDC: "Take medicines as prescribed, even if you feel fine." Missed insulin shots are one of the two most common causes of DKA. "No more blood sugar monitoring, test strips, insulin injections" Blood Sugar Blaster CDC: "Check your blood sugar often, especially if you're sick." "Dealing with countless medications and injections? They will all be a thing of the past!" CelluFend and Insufend, word for word MedlinePlus lists not taking "your medicines correctly" among the causes of hyperglycemia. "This Diabetes Breakthrough Candy Takes You Off Your T2D Meds" (page title) GlucoTrust Bites NIDDK: "Take your medicines as they were prescribed, even if you feel good or have reached your blood glucose, blood pressure, or cholesterol goals." Sales pages read on September 25 and 27, 2026 (see each review). CDC, "Diabetic Ketoacidosis" (May 15, 2024); NIDDK, "Managing Diabetes" (October 2023); MedlinePlus, "Hyperglycemia" (May 10, 2024). Read on September 27, 2026. Herbs and medicines can also interact in the other direction: NCCIH describes a study in healthy adults where taking goldenseal extract with metformin lowered metformin levels about 25 percent, a drop "enough to potentially hinder glucose control in people with type 2 diabetes taking metformin." ## Frequently asked questions **My blood sugar is over 300. What should I do?** If it stays at 300 mg/dL or above, the CDC says to go to the emergency room or call 911 right away. Same if your breath smells fruity, you're vomiting and can't keep anything down, you're having trouble breathing, or you have multiple signs and symptoms of DKA. **What are the symptoms of high blood sugar?** Feeling thirsty, tired or weak, headaches, urinating often and blurred vision, according to MedlinePlus. Many people with type 2 diabetes or prediabetes have no symptoms at all. **What blood sugar level is too high?** With diabetes, the NIDDK says above 180 mg/dL for most people. On a lab test, the CDC counts a fasting level of 126 mg/dL or above as the diabetes range, and a random test of 200 mg/dL or above counts too; the NIDDK says the random test is used when there are symptoms. The emergency line is a reading that stays at 300 mg/dL or above. **Can you have high blood sugar without diabetes?** Less commonly, yes. MedlinePlus names pancreas or adrenal problems, certain medicines and severe illnesses. A high reading from a pharmacy or health fair is worth taking to your doctor, who may re-test you, the CDC says. **Can a supplement bring high blood sugar down?** NCCIH says "for most supplements, there isn't evidence to support a beneficial effect on diabetes or its complications," and calls it "very important not to replace medical treatment for diabetes with an unproven health product or practice." ## Related pages Blood sugar basics ### [Low blood sugar (hypoglycemia): what to do in the first 15 minutes](https://glucosebench.com/low-blood-sugar) For most people with diabetes, blood sugar below 70 mg/dL is low, according to the CDC and the NIH; for people without diabetes, MedlinePlus says hypoglycemia is… Read more Blood sugar basics ### [Normal blood sugar levels, and why a diabetes target is a different number](https://glucosebench.com/blood-sugar-levels) For adults without diabetes, the CDC calls a fasting blood sugar of 99 mg/dL or below normal, 100 to 125 mg/dL prediabetes, and 126 mg/dL or above diabetes; an A1C below… Read more Blood sugar basics ### [Which blood test diagnoses diabetes? All four, compared](https://glucosebench.com/diabetes-tests) Type 2 diabetes and prediabetes are diagnosed with blood tests: the A1C, the fasting plasma glucose test, the oral glucose tolerance test (OGTT) and, when there are… Read more Blood sugar basics ### [Checking your blood sugar at home: the steps, the timing and a log worth keeping](https://glucosebench.com/check-blood-sugar-at-home) The CDC's steps for checking blood sugar at home: wash your hands with soap and warm water and dry them well, prick your finger with a lancet, put a small drop of blood… Read more Updated September 27, 2026. [See our full method](https://glucosebench.com/how-we-choose) --- ## GlucoseBench - GlucoseBench, published by Grupo Marfre Automação e Tecnologia (Contagem, Brazil) - Email: contact@glucosebench.com - Home: https://glucosebench.com/ - llms.txt: https://glucosebench.com/llms.txt · llms-full.txt: https://glucosebench.com/llms-full.txt · sitemap: https://glucosebench.com/sitemap.xml