High Blood Sugar (Hyperglycemia): Signs, Causes, When to Act

This site's low blood sugar article covers the drop that comes on fast. High blood sugar is the opposite reading, and it usually behaves differently. The NHS says its symptoms usually come on gradually and may only start when the level gets very high, and the NIDDK says many people with type 2 diabetes have no symptoms at all, or symptoms so mild they might not notice them.

This article covers what high blood sugar is, the numbers doctors use, the symptoms, the overlap with prostate symptoms, the common causes, high blood sugar without diabetes, ketones, the two emergencies to know by name, and what helps. It sits in the Energy section because tiredness is on every symptom list, though, in our reading, it is far from the most specific sign.

What high blood sugar is

MedlinePlus says high blood sugar, also called high blood glucose or hyperglycemia, almost always happens in people who have diabetes. It occurs when the body makes too little insulin, or does not respond to the signal insulin sends.

Insulin is the hormone that moves glucose from the blood into muscle or fat, where it is stored for later use as energy. When that fails, too much glucose stays in the blood.

MedlinePlus also describes a temporary version: high blood sugar sometimes occurs due to stress from surgery, infection, trauma or medicines, and blood sugar returns to normal after the stress is over.

The numbers doctors use

For diagnosing diabetes from high blood sugar in adults who are not pregnant, the NIDDK's test page gives a table sourced to the American Diabetes Association. Diabetes is an A1C of 6.5% or above, a fasting plasma glucose of 126 mg/dL or above, or a result of 200 mg/dL or above two hours into an oral glucose tolerance test.

A random plasma glucose of 200 mg/dL or above also counts, but that test is used when there are symptoms.

Prediabetes sits below those lines: an A1C of 5.7% to 6.4%, a fasting glucose of 100 to 125 mg/dL, or 140 to 199 mg/dL on the glucose tolerance test. This site's prediabetes after 40 article covers that range in detail.

The NIDDK adds that the A1C test might not be accurate in some situations, such as certain types of anemia or other blood problems, that a doctor usually uses a second test to confirm diabetes, and that a home blood glucose meter cannot diagnose it.

The full NIDDK table for adults who are not pregnant, sourced to the American Diabetes Association:

For a man who already has diabetes, the diagnostic cutoffs are not the daily target. MedlinePlus says you and your provider set a target goal for blood sugar levels at different times of the day, and decide how often to check at home.

The NHS gives its own home-test guide in the units used in the UK and also says those levels are a guide that may differ with your age and type of diabetes.

The symptoms

For high blood sugar, MedlinePlus lists being very thirsty or having a dry mouth, blurry vision, dry skin, feeling weak or tired, and needing to urinate a lot, or needing to get up more often than usual at night to urinate. Its hyperglycemia page adds headaches. The NHS list adds losing weight.

MedlinePlus says that over time high blood sugar weakens the immune system and makes infections more likely.

The NIDDK's list of common diabetes symptoms overlaps: increased urination, feeling very thirsty, feeling very hungry even after eating, blurred vision, fatigue, sores that do not heal, and frequent infections, such as urinary tract or skin infections.

For type 2 diabetes, it says symptoms can develop slowly over several years, and that some people find out they have it when they develop other problems, which it lists as pain, numbness or tingling in the feet or hands, sexual problems, chest pain and vision loss.

Peeing at night: prostate or blood sugar?

Getting up at night to urinate is on the MedlinePlus high-blood-sugar list, and it is also a common symptom of an enlarged prostate, covered in this site's prostate section. In our reading, the two are worth separating rather than assuming: a man who blames his prostate may never have his blood sugar checked, and the reverse is also possible.

In our reading, a few clues help:

• Points toward blood sugar: thirst, a dry mouth and, per the NHS, weight loss.
• Points toward the prostate: in this site's prostate articles, a weak stream or a feeling that the bladder hasn't emptied; see weak urine stream and waking up to pee at night.

Sexual problems, also on the NIDDK's list, are covered in testosterone and erectile dysfunction. A blood test shows whether blood sugar is part of it, and the two can coexist.

What pushes blood sugar up in diabetes

The NHS names the common causes in people with diabetes: being unwell, feeling stressed, eating too much sugary or starchy food, being less active than usual, and missing doses of diabetes medicine. It adds that high blood sugar can happen if the medicine isn't working well, if you take certain medicines such as steroids, or after a recent operation.

MedlinePlus turns this into questions to ask yourself when your sugar runs high. Among them:

• Are you following your meal plan and taking your medicines correctly?
• If you use insulin, is the dose right, is it expired, and has it been stored too hot or too cold?
• Have you been less active, ill, dehydrated or stressed?
• Have you gained weight?
• Have you started a new medicine, including one for high blood pressure?
• Have you had a glucocorticoid (steroid) injection into a joint or elsewhere?

High blood sugar without diabetes

MedlinePlus says that, less commonly, people without diabetes can get high blood sugar, from conditions that affect insulin or glucose levels, including problems with the pancreas or adrenal glands, certain medicines, and severe illnesses. If you don't have diabetes and are having symptoms, it says to see your provider to find out the cause and how to treat it.

The NHS says the same in its own terms: speak to your GP practice if you have symptoms of high blood sugar and have not been diagnosed with diabetes. In the U.S., the equivalent is your primary care provider; the NIDDK says the random plasma glucose test is the one doctors may use when you have symptoms and they do not want to wait for you to fast.

Ketones: the reading that changes the urgency

Ketones are acids the liver makes from fat. MedlinePlus says they become dangerous when too little insulin makes them build up fast. MedlinePlus says that with type 2 diabetes, if your blood sugar is higher than your goals over 3 days and you don't know why, check your urine for ketones; with type 1 diabetes, after 6 hours.

If ketones are present, it says to contact your provider or seek emergency medical care; its ketoacidosis page says to contact your provider right away and not to delay, and the NHS treats a high ketone level as an emergency.

Its hyperglycemia page adds that if you have an at-home ketone test, check every 4 to 6 hours when your blood glucose is very high or you have DKA symptoms such as nausea, vomiting, belly pain or trouble breathing, and that if ketones are moderate or high, or if you don't have a test, contact your provider right away or get emergency medical help.

The two emergencies to know by name

Diabetic ketoacidosis (DKA). MedlinePlus calls DKA a life-threatening problem in which fat is broken down too fast and ketones make the blood acidic. Common symptoms include decreased alertness, deep and rapid breathing, dry skin and mouth, a flushed face, frequent urination or thirst lasting a day or more, fruity-smelling breath, headache, muscle aches, nausea and vomiting, and stomach pain.

It says DKA is sometimes the first sign of type 1 diabetes, and that people with type 2 diabetes can also develop a form of it.

Hyperosmolar hyperglycemic syndrome (HHS). MedlinePlus describes HHS as a complication of type 2 diabetes, with extremely high blood sugar, extreme dehydration and, in many cases, decreased alertness. It may also occur in people not yet diagnosed with diabetes.

Symptoms include increased thirst and urination at first, weakness, nausea, weight loss, a dry mouth and tongue, fever, seizures, confusion and coma, and may get worse over days or weeks. Risk factors include older age, impaired thirst, poor kidney function, and running out of diabetes medicine.

Side by side, from the two MedlinePlus pages:

What years of high blood sugar do

The NHS says it is not usually a serious problem if blood sugar is sometimes slightly high for a short time. If it stays high for long or gets very high, it can lead to permanent nerve damage in the hands and feet, permanent damage to the eyes, heart disease and stroke, and life-threatening conditions such as diabetic ketoacidosis.

This site's metabolic syndrome article covers fasting blood sugar as one of the five numbers that make up that syndrome.

What helps bring it down

To lower high blood sugar if you have diabetes, the NHS says to take any diabetes medicine as advised, avoid too much sugary or starchy food, find ways to manage stress, exercise regularly, lose weight if you're overweight, and follow your care team's advice for sick days.

It says not to skip or change doses of diabetes medicine unless advised, and to speak to your care team if your level stays high or symptoms continue despite trying.

MedlinePlus says that if you have diabetes and often have high blood glucose, your health care team may change your meal plan, activity plan or medicines, and that severe hyperglycemia with symptoms of DKA needs treatment in the hospital, often with intravenous fluids and insulin. For HHS, it suggests a sick-day plan and ordering diabetes medicines in 3-month amounts so you are less likely to run out.

Is high blood sugar behind your tiredness?

Feeling weak or tired is on both the MedlinePlus and NHS lists of high blood sugar symptoms, so the question is fair. In our reading, the sources cut both ways: tiredness can be a symptom, but the NIDDK says many people with type 2 diabetes have no symptoms, so feeling fine proves nothing either.

A blood test shows whether blood sugar is high; whether it explains the tiredness is a question for your provider. For the many other reasons men feel worn out, see this site's fatigue after 40 article.