by ron
(illinois usa)
QUESTION: I keep having high readings like 458, 420, or sometimes my meter says “HI.” I have not been diagnosed with diabetes and was planning to see my doctor next week. What should I do?
Blood sugar readings of 420–458 mg/dL, or a meter reading of “HI,” require emergency medical evaluation now—especially in someone who has not yet been diagnosed with diabetes. Do not wait until next week or delay care to fast for an outpatient test. Recheck once with clean, dry hands and a new strip, but if the result remains above 400 mg/dL or says “HI,” go to the nearest emergency department. Call 911 if you have vomiting, abdominal pain, rapid or difficult breathing, confusion, severe weakness, fainting, fruity-smelling breath, or cannot travel safely.
Answer by Dr. Albana Greca, MD, MMedSc
Hi Ron,
These readings are dangerously high. A home glucose meter cannot diagnose diabetes by itself, but repeated results in this range may indicate severe hyperglycemia and can occur with diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS). Both conditions can cause serious dehydration, abnormal electrolytes, loss of consciousness, and other life-threatening complications.
If urine or blood ketone strips are immediately available, you may check ketones while arranging care, but do not delay leaving for the emergency department to obtain or repeat a ketone test.
“HI” generally means the glucose level is above the meter’s reportable range. The exact cutoff differs by meter, so check the device manual. With readings already reaching 420–458 mg/dL, however, a “HI” result should be treated as potentially severe hyperglycemia rather than assumed to be a device error.
Emergency clinicians may repeat the glucose with a laboratory test and check electrolytes, kidney function, blood or urine ketones, acid-base balance, hydration, and signs of infection or another trigger. Tell them about all medicines you use, especially steroid tablets, injections, creams, or inhalers, because steroids can raise blood glucose.
After the immediate problem is treated, your clinician can determine whether you have diabetes and which type. Common diagnostic tests include an HbA1c, fasting plasma glucose, and sometimes a random plasma glucose test. An HbA1c does not require fasting. A fasting glucose test normally requires at least eight hours without food, but you should not fast at home while waiting for care with readings this high. You can read more about blood tests used to diagnose diabetes.
Call 911 immediately for confusion, fainting, severe drowsiness, repeated vomiting, abdominal pain, rapid or labored breathing, chest pain, severe dehydration, inability to keep fluids down, or fruity-smelling breath. Do not drive yourself if you feel weak, dizzy, confused, or unwell.
Ron, please do not wait for a routine appointment next week. Repeated glucose readings above 400 mg/dL in a person without a diabetes diagnosis need same-day emergency assessment. Bring your meter, test strips, glucose record, medicine list, and identification with you.
Educational safety note: This answer is for general diabetes education only. It does not replace personal medical advice, diagnosis, or treatment. Do not start, stop, or change medicines, supplements, diet, or exercise plans without speaking with your healthcare provider.
Last reviewed: July 2026.
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