Blood sugar tests and HbA1c are two of the most common numbers people see on a lab report, and they answer different questions. This guide explains what each measures and how the standard criteria define the thresholds, so you can read your results with more confidence. It does not diagnose anything: that is a clinician’s job.
This article is educational and does not replace clinical training or advice for a specific patient. All clinical decisions rest with the treating clinician.
What HbA1c and Blood Sugar Are
Blood sugar (blood glucose) is a snapshot. It tells you how much glucose is in your blood at the moment the sample is taken, which is why the timing of the test matters and why fasting, random, and post-load values are read differently.
HbA1c is a longer view. HbA1c reflects the average blood glucose over the past roughly 90 days (NCBI Bookshelf). Because it averages over months, a single meal or a stressful morning does not swing it the way it can swing a spot glucose reading. The two tests complement each other rather than replace one another.
How to Read Your Results Step by Step
Reading these numbers is a process, not a single glance. Work through the steps below in order.
Step 1: Identify which test you are looking at
Check the label on the report. An HbA1c result is reported as a percent. A blood glucose result is reported in mg/dL or mmol/L and should note whether it was fasting, random, or a 2-hour value from an oral glucose tolerance test (OGTT). You cannot compare the numbers correctly until you know which is which.
Step 2: Compare against the standard criteria
Once you know the test, place the value against the standard criteria. For HbA1c, below 5.7 percent is normal, 5.7 to 6.4 percent indicates prediabetes, and 6.5 percent or higher is diagnostic for diabetes (NCBI Bookshelf). For glucose, the diabetes diagnostic thresholds are a fasting plasma glucose at or above 126 mg/dL (7.0 mmol/L); a random plasma glucose at or above 200 mg/dL (11.1 mmol/L) with symptoms; or an OGTT 2-hour glucose at or above 200 mg/dL (11.1 mmol/L) (NCBI Bookshelf).
Step 3: Note that a single value is not a diagnosis
A number above a threshold is a signal, not a verdict. A diagnosis usually needs confirmation and is made by a clinician (NCBI Bookshelf). Treat any single reading as a reason to talk to a clinician, not as a conclusion in itself.
Standard Reference Values
The table below summarizes the thresholds as defined by the cited standard criteria. Reference ranges can vary by lab and by the units your lab reports, so always read your own report against the range printed on it.
| Test | Category | Value (standard criteria) |
|---|---|---|
| HbA1c | Normal | Below 5.7 percent (NCBI Bookshelf) |
| HbA1c | Prediabetes | 5.7 to 6.4 percent (NCBI Bookshelf) |
| HbA1c | Diagnostic for diabetes | 6.5 percent or higher (NCBI Bookshelf) |
| Fasting plasma glucose | Diabetes threshold | At or above 126 mg/dL (7.0 mmol/L) (NCBI Bookshelf) |
| Random plasma glucose (with symptoms) | Diabetes threshold | At or above 200 mg/dL (11.1 mmol/L) (NCBI Bookshelf) |
| OGTT 2-hour glucose | Diabetes threshold | At or above 200 mg/dL (11.1 mmol/L) (NCBI Bookshelf) |
Common Mistakes When Reading These Numbers
A few errors come up again and again:
- Comparing an HbA1c percent against a glucose threshold, or vice versa. They are different scales and different tests.
- Reading a random glucose as if it were a fasting glucose. The random threshold applies only when symptoms are present, per the standard criteria (NCBI Bookshelf).
- Treating one over-threshold value as a finished diagnosis. Diagnosis usually needs confirmation and is made by a clinician (NCBI Bookshelf).
- Ignoring the lab’s own printed reference range. Ranges vary by lab, so the range on your report is the one that applies to your sample.
When to See a Clinician
If any of your values fall at or above the thresholds in the table, or if the report flags a result as out of range, bring it to a clinician. Because a diagnosis usually needs confirmation and is made by a clinician (NCBI Bookshelf), a clinician is the right person to decide whether repeat or additional testing is needed and what the numbers mean for you specifically. This is especially important if you have symptoms alongside a high reading.
How Phở Can Help
Phở can help you organize what a report says and point you to the source behind each threshold, so you can read your numbers alongside the standard criteria rather than guessing. When a claim is not backed by a source, Phở labels it as unverified rather than inventing a value. Phở does not diagnose and does not offer treatment or dosing advice: those decisions rest with a clinician.
References
- HbA1c thresholds and what HbA1c reflects: https://www.ncbi.nlm.nih.gov/books/NBK549816/
- Diabetes glucose diagnostic thresholds (fasting, random, OGTT): https://www.ncbi.nlm.nih.gov/books/NBK278985/
- Diagnosis usually needs confirmation and is made by a clinician: https://www.ncbi.nlm.nih.gov/books/NBK554615/