Blood Sugar 155 mg/dl — Too High? Fasting & After Eating
Where 155 mg/dl sits — adjust to your situation
155 mg/dl as a fasting reading
Diabetes range
A fasting reading of 126 mg/dl or higher falls into the diabetes range. Diagnosis requires a repeat test on another day — take this result to your doctor.
Fasting = no food for at least 8 hours, typically first thing in the morning. More on fasting readings.
155 mg/dl after eating
Prediabetes range
Between 140 and 199 mg/dl two hours after a meal suggests impaired glucose tolerance, the post-meal form of prediabetes.
Guidelines measure 2 hours after the start of a meal. More on post-meal readings.
The one-hour 155: a research marker, not a US diagnosis
Most people know the two-hour cut-off of the glucose tolerance test: under 140 normal, 140 to 199 impaired, 200 or more diabetes. Fewer know that researchers have long studied the one-hour value too. In a number of long-term studies, people whose glucose was 155 or more one hour into a 75 g glucose tolerance test were more likely to develop type 2 diabetes later, even if their two-hour value was normal.
In the US, this is not part of the official diagnostic criteria. ADA does not use a one-hour cut-off for diagnosing prediabetes or diabetes outside pregnancy. If your lab report shows a one-hour 155, it will not be labeled as an abnormal result by US standards, but it may be worth a conversation.
Think of the one-hour value as an early-warning light rather than a verdict. It points to people who may benefit from closer follow-up, but it does not decide treatment on its own, and a single result can vary from one test day to the next. Researchers are still working out which cut-off works best, and whether acting on it changes long-term outcomes.
Why the first hour may show change earlier
The shape of the glucose curve depends on how fast insulin is released after sugar arrives. In healthy people, the pancreas responds with a quick first burst of insulin that limits the peak. One of the earliest changes on the way to type 2 diabetes is that this early burst becomes smaller or slower. The peak then climbs higher, but later insulin release may still bring glucose back down by two hours. A test that only looks at the two-hour point would call this normal; the one-hour value shows the strain.
That is the reasoning behind the research interest. It is also why a high one-hour and a normal two-hour value is sometimes described as “intermediate” risk rather than as a disease.
A home reading of 155 one hour after a meal is different
The research marker comes from a standardized test: an overnight fast, then 75 g of glucose as a drink, blood drawn from a vein. A finger-stick one hour after a home meal is not comparable. Meals vary in carbohydrate, fat and fiber, and many healthy people reach the 150s at one hour after a starchy meal. Outside pregnancy, a one-hour home value of 155 is generally unremarkable. In pregnancy, where the one-hour goal is under 140, it is above target and worth reporting.
What to do with this information
- If an OGTT showed a one-hour value of 155 or more with a normal two-hour value, ask whether your doctor wants to repeat testing sooner than usual, especially if you have other risk factors.
- The steps that help prediabetes also suit people in this grey zone: regular activity, weight loss if needed, and meals built around vegetables, protein and fiber.
- Keep an eye on A1C and fasting glucose over the years. They remain the standard markers in the US.
For the standard ranges, see the blood sugar after eating page.
Measured right after exercise?
There is no official range for readings taken during or just after a workout, so the two classifications above do not apply to them. How exercise moves blood sugar.
How 155 mg/dl compares to a typical day
Typical day without diabetes; your reading is the horizontal line — higher than a typical day reaches two hours after a meal; brief one-hour peaks this high are common.
What to do with a reading of 155 mg/dl
Book a doctor's appointment to confirm with a lab test (fasting glucose or A1C). If you are already diagnosed, this reading belongs in your log for your care team.
What actually moves the number: How to lower blood sugar, Foods that steady your glucose and Exercise and blood sugar.
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Questions about 155 mg/dl
Is 155 mg/dl blood sugar normal?
It depends on when you measured. Fasting, 155 mg/dl is diabetes range (normal fasting range: 70–99 mg/dl). Two hours after a meal it is prediabetes range (normal post-meal range: 70–139 mg/dl).
What is 155 mg/dl in mmol/L?
155 mg/dl equals 8.6 mmol/L. Divide mg/dl by 18 to convert (used in the UK, Canada, Australia and most of Europe).
Does one reading of 155 mg/dl mean I have diabetes?
No single home reading is a diagnosis. Guidelines require a second abnormal lab result, either a different test from the same blood draw or a repeat on another day (fasting glucose, an oral tolerance test, or A1C). But a reading like this is exactly the reason those tests exist — take it to your doctor.
How accurate is a home reading of 155 mg/dl?
Home meters are allowed an error of ±15 mg/dl below 100 mg/dl and ±15 % from 100 up (ISO 15197), so a displayed 155 can correspond to a true value anywhere from 132 to 178 mg/dl. Fasting, the entire window stays inside the diabetes range band — this classification is robust even to meter error. After a meal, the window touches the 140 mg/dl boundary.
What A1C would 155 mg/dl correspond to?
If 155 mg/dl were your average glucose over three months, it would work out to an A1C of about 7 % — at or above the 6.5 % diabetes threshold. A single reading is not an average — but the conversion shows what this level would mean as a habit. How the two measures relate: A1C and blood sugar.
Why don’t US guidelines use the one-hour value?
Guidelines change slowly and need agreement on exact cut-offs, testing protocols and what treatment should follow. The two-hour value, fasting glucose and A1C have decades of outcome data behind them. Research on the one-hour value is ongoing, and guidelines may change if the evidence becomes strong enough.
Should I ask for a one-hour sample at my next OGTT?
You can ask, and some labs take one routinely. Keep in mind that the result will be interpreted alongside your two-hour value, A1C and risk factors, not on its own.
BloodSugarEasy — blood sugar reading report
Reading: 155 mg/dl (8.6 mmol/L)
Fasting classification: Diabetes range · After-meal classification: Prediabetes range
Reference: ADA criteria, reviewed 2026-11-03 · https://bloodsugareasy.com/blood-sugar-155/
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