Blood Sugar 516 mg/dL: Emergency Warning Signs, DKA, HHS and What to Do

Direct answer

If a finger-stick reading of 516 mg/dL is real, especially with frequent urination or fatigue, go to an emergency department now. The meter does not diagnose DKA or HHS, and a number under 600 is not a reason to stay home.

The figure 600 mg/dL is one diagnostic criterion for HHS, taken from plasma glucose in a laboratory. It is not a line below which home care is safe. The full criteria are in the table later on this page. This page is general information and does not assign a diabetes type from a meter photo.

What to do now, and what not to do

The CDC page dated 15 May 2024 says to go to the emergency department or call emergency services if blood sugar stays at 300 mg/dL or above, if breath smells fruity, if vomiting prevents keeping food or drinks down, if breathing is difficult, or if several signs of diabetic ketoacidosis are present. The word “stays” is not permission to watch a reading of 516 overnight when symptoms are already there.

The CDC sick-day page from the same date says that fatigue or unclear thinking is a reason for someone else to drive.

Do not use the low-glucose page for this reading

The page on a morning glucose of 41 mg/dL is the opposite problem. Juice used for a low reading is not the treatment for 516. The pages on a post-meal glucose of 110 to 120 and on silent prediabetes screening answer different questions.

Why glucose can stay high without food

Even without a meal, the liver can still make and release glucose into the blood. When insulin is insufficient, or the body responds poorly to insulin, glucose accumulates. When insulin deficiency is severe, the body may break down fat and make more ketones, which can lead to acidosis. Glucose production and ketone production are different processes, even though they can occur together.

The liver still releases glucose

Skipping food does not switch off hepatic glucose release. The CDC explains that illness hormones can raise glucose even when a person is not eating much. An earlier meal may contribute, but one meal should not be treated as the whole explanation of 516.

Insufficient insulin does not mean every cell is blocked

Some cells use glucose without insulin. Many others need insulin. When insulin is low or the response is poor, glucose remains in the blood. ADA 2026 section 6 says people on intensive insulin should not stop basal insulin even if they are not eating. That is a principle, not a dose to start from a meter photo.

Ketones are a separate process

The CDC explains that when insulin is too low, the body breaks fat down and produces ketones. High ketones together with acidosis are a core part of DKA. Fat breakdown is not the whole explanation of a high glucose.

Frequent urination and water loss

Very high glucose pulls water out through the urine, so thirst, fatigue, and dehydration can appear while the person can still walk. ADA 2026 says a hyperglycemic crisis should be considered with frequent urination, thirst, weight loss, vomiting, dehydration, or a change in thinking. Mild fatigue does not remove that concern.

What DKA is

Diabetic ketoacidosis develops when there is not enough insulin, ketone production rises, and the blood becomes acidic. It occurs in type 1 and type 2 diabetes and can be the first sign of diabetes that has not yet been diagnosed. The CDC lists illness, missed insulin, a pump problem, or a wrong dose as common causes, and also heart attack, stroke, physical injury, alcohol, and some medicines such as diuretics and corticosteroids.

Early symptoms are thirst and much more urine. Later signs can include fast deep breathing, dry skin and mouth, a flushed face, fruity breath, headache, muscle aches, severe tiredness, nausea, vomiting, and stomach pain. A meter photo does not show whether that set of signs is present.

What HHS is, and why 600 is not a safety line

Hyperglycemic hyperosmolar state is marked by very high glucose and concentrated blood, usually with large fluid losses and often with another illness. ADA 2026 says suspected HHS should be evaluated and treated in hospital immediately.

The glucose criterion is plasma glucose of 600 mg/dL or higher, and the osmolality, ketone, and acid-base criteria must also be met. A finger-stick of 516 is not a plasma result. It cannot show that HHS is present or absent, and it is not a reason to stay home when urination is frequent or the person is tired.

ADA notes that about one-third of hyperglycemic emergencies are a mix of DKA and HHS. A number between 200 and 600 does not place the person in a safe category. About 10 percent of DKA presents with plasma glucose under 200 mg/dL, so a lower number is not proof against DKA either.

How DKA and HHS differ

This table follows ADA Standards of Care 2026, section 16, Tables 16.1 and 16.2. ADA states that the tables are adapted from the 2024 consensus report on hyperglycemic crises in adults (Diabetes Care 2024;47:1275). Every required element must be present. The glucose row alone is not a diagnosis.

ADA describes care of mild, uncomplicated DKA in an emergency department when the person is hemodynamically and cognitively intact, can drink, and can take subcutaneous insulin under a clinical plan. That exception is not a reason to stay home with a reading of 516 and symptoms. This page does not give an insulin dose.

Why the number alone cannot diagnose

DKA needs three elements together: glucose or known diabetes, ketones, and acidosis. HHS needs plasma glucose, high osmolality, the absence of significant ketones, and the absence of acidosis. A reading of 516 is high enough to go to the emergency department. It is not a completed diagnosis.

What ketone testing is for

A care team may ask for blood or urine ketones as part of that person’s plan. The CDC advises checking when someone is ill or glucose is 250 mg/dL or higher, and when DKA symptoms are present. High ketones are an emergency.

When glucose is already very high and symptoms are present, going out to buy a kit should not delay the hospital. A negative home test does not prove safety, because HHS is defined with ketones that are not markedly high and still needs hospital treatment.

How a finger-stick meter can be wrong

The FDA says even a small amount of food or sugar on a finger can change the result. Wash and dry the hands, and do not squeeze the finger hard. Home meters are not as accurate as hospital testing. Dehydration, shock, or an abnormal hematocrit can also make a reading wrong.

If glucose is suspected to be very high, go to the emergency department even when the meter is doubted. One recheck is reasonable. Several rechecks do not replace a laboratory test.

Food, stopped medicine, illness, and insulin

Stopping medicine can matter. The CDC lists missed insulin as a common cause of DKA, but the medicine list and the timing have to be known before anyone draws a conclusion. People stop medicine for many reasons. This page does not blame them.

SGLT2 inhibitors are one setting ADA links with ketoacidosis even when glucose is not very high. Tell the team the medicine names. Do not stop or start a medicine tonight as a self-decision. A sick-day plan already taught by the person’s own clinician may be followed while help is being sought. It must not delay emergency assessment for this reading.

What the emergency department may check

Clinicians may check laboratory glucose, ketones, electrolytes, kidney function, and acid-base status when indicated, and look for a trigger such as infection. Treatment is intravenous fluid, insulin, and correction of electrolyte abnormalities in hospital. This page does not give a home fluid or insulin recipe.

Why not to exercise or keep fasting

The American Diabetes Association says that if glucose is above 240 mg/dL, check urine ketones, and do not exercise if ketones are present, because exercise may push glucose higher. Its physical-activity position statement says that at 350 mg/dL or higher, ketones should be checked, and moderate-to-large ketones mean no exercise.

The row that allows light activity when ketones are negative is about planned exercise in someone who feels well. It is not an option for a person with glucose of 516 plus frequent urination or fatigue. Do not exercise on the way to the hospital. Further fasting does not switch off glucose release from the liver.

After the acute episode

ADA 2026 section 16 advises a discharge plan fitted to the person, and follow-up with primary care, endocrinology, or a diabetes care and education specialist within 1 month. If medicines changed or glucose is not at goal, an earlier visit in 1 to 2 weeks is preferred.

HbA1c, the reason glucose rose, medicines that had been stopped, and a dietitian review belong to that follow-up. An HbA1c result is not something to wait for before going to the emergency department.

Questions people ask

How the author explains the mechanism

Asst. Prof. Dr. Norawit Raatpiboon separates three processes that are often collapsed into one sentence. The liver can make and release glucose even without food. Insufficient insulin, or a poor response to insulin, lets glucose accumulate in the blood. Severe insulin deficiency increases fat breakdown and ketones. High glucose also pulls water into the urine, so dehydration can develop before the person becomes drowsy.

Limits of this page

This page is general information. It does not diagnose DKA, HHS, or a diabetes type from a meter photo, and it does not give an insulin dose or tell anyone to stop or increase medicine. If the person is drowsy, confused, vomiting heavily, breathing abnormally, or getting worse, call 1669.