Table of Contents[Hide][Show]
- LISTEN TO THE PODCAST
- CHAPTERS
- Tests Used To Diagnose Diabetes
- Diabetes Diagnostic Criteria: The Numbers Used To Diagnose Diabetes
Case Study Examples of Diagnosis+−
- Emma, 2 different high test results, confirmed type 2 diabetes diagnosis
- John, diabetes symptoms and one high test result, confirmed type 2 diabetes diagnosis
- Taryn, A1c prediabetes range, oral glucose test T2Diabetes range, confirmed type 2 diabetes diagnosis
- Amanda, A1c normal range, fasting blood glucose T2Diabetes range, should be confirmed with a second test unless a person is symptomatic
- Conclusion
- Transcript
Have you ever walked out of your doctor’s office feeling confused about how your diabetes diagnosis was made?
Maybe one test looked normal, but another didn’t, and suddenly you’re handed a label that feels permanent and overwhelming.
In this episode, we’ll explore the medical care guidelines to understand how diabetes is actually diagnosed—the criteria—and why the process can be more complex than it first appears.
LISTEN TO THE PODCAST
CHAPTERS
3:35 Hemoglobin A1c test (HbA1c or A1c)
4:48 Fasting blood glucose test (FBG)
6:10 Oral glucose tolerance test (OGTT)
7:02 Random glucose test
8:29 EMMA: No symptoms, two high tests on same day
9:54 JOHN: Symptoms, one high test
12:37 TARYN: Prediabetes A1c, type 2 diabetes OGTT
17:41 AMANDA: Normal A1c, high fasting blood sugar23:36 Can diabetes diagnostic tests be inaccurate?
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Tests Used To Diagnose Diabetes
There are four tests commonly used to diagnose type 2 diabetes:
- Hemoglobin A1c (HbA1c): An A1c test reflects your average blood sugar levels over the past 3 months. It’s convenient and widely used, but it doesn’t always catch post-meal spikes early.
- Fasting Blood Glucose (FBG): This test is taken after at least 8 hours of fasting. This test can be affected by stress, poor sleep, recent illness and other things.
- Oral Glucose Tolerance Test (OGTT): This test measures your blood glucose levels two-hours after consuming a 75g glucose drink. This test is particularly helpful in identifying early post-meal glucose issues.
- Random Blood Glucose: If symptoms of diabetes are present, this test can be used to confirm a diagnosis.
Diabetes Diagnostic Criteria: The Numbers Used To Diagnose Diabetes
| Test | Normal | Prediabetes | Type 2 Diabetes |
|---|---|---|---|
| HbA1c (Glycated Hemoglobin) | < 5.7% (< 39 mmol/mol) | 5.7–6.4% (39–46 mmol/mol) Outside USA: 6.0–6.4% (42–46 mmol/mol) | ≥ 6.5% (≥ 48 mmol/mol) |
| Fasting Plasma Glucose (after 8+ hours fast) | < 100 mg/dL (< 5.6 mmol/L) Outside USA: < 6.1 mmol/L | 100–125 mg/dL (5.6–6.9 mmol/L) Outside USA: 6.1–6.9 mmol/L | ≥ 126 mg/dL (≥ 7.0 mmol/L) |
| Oral Glucose Tolerance Test (2 hrs after 75g glucose drink) | < 140 mg/dL (< 7.8 mmol/L) | 140–199 mg/dL (7.8–11.0 mmol/L) | ≥ 200 mg/dL (≥ 11.1 mmol/L) |
| Random Blood Glucose (with symptoms) | – | – | ≥ 200 mg/dL (≥ 11.1 mmol/L) with symptoms |
Case Study Examples of Diagnosis
We begin with two straightforward examples.
Emma, 2 different high test results, confirmed type 2 diabetes diagnosis
Emma: went for her routine annual check-up. She wasn’t feeling unwell, but her doctor included blood sugar tests as part of her standard blood work. Her fasting glucose came back at 132 mg/dL (7.3 mmol/L) and her A1c was 6.7%.
Both test results were above the diagnostic thresholds for type 2 diabetes. Even though Emma felt fine, her doctor could confidently confirm a diagnosis because two different tests were in the diabetic range.
John, diabetes symptoms and one high test result, confirmed type 2 diabetes diagnosis
John: had been feeling unusually thirsty, tired, and was getting up several times during the night to urinate. He visited his doctor to discuss these symptoms. His doctor did a random blood glucose test, which came back at 228 mg/dL (12.6 mmol/L). Because John had clear symptoms and a high blood glucose reading above 200 mg/dL (11.1 mmol/L), a diagnosis of type 2 diabetes could be made immediately, without needing a second test.
But what happens when test results don’t match?
Here are two real-world case studies that highlight the confusion many people experience:
Taryn, A1c prediabetes range, oral glucose test T2Diabetes range, confirmed type 2 diabetes diagnosis
Taryn: was told she had type 2 diabetes after doing an oral glucose tolerance test (OGTT), even though her A1c was only 6.0%, which falls into the prediabetes range. Her 2-hour OGTT result, however, was in the diabetic range at 11.1 mmol/L (200 mg/dL) or above. She had a high OFTT and prediabetes A1c level.
According to the guidelines, when two tests are done at the same time and one result shows prediabetes while the other confirms diabetes, a diagnosis of type 2 can be made.
In Taryn’s case, the OGTT picked up on a post-meal spike that the A1c missed. Higher than normal post-meal levels, is an early sign that her body is struggling to manage glucose after eating. The diagnosis felt sudden, but it was based on early detection and gave her the chance to intervene with nutrition and lifestyle changes.
Amanda, A1c normal range, fasting blood glucose T2Diabetes range, should be confirmed with a second test unless a person is symptomatic
Amanda: had the opposite experience. She felt anxious before a recent blood test, which showed a fasting blood glucose of 7.0 mmol/L (126 mg/dL), a number that is right at the threshold for a diabetes diagnosis. But her A1c level was only 5.6%, a completely normal result. High fasting blood sugar levels but normal A1c, yet she was given a diagnosis of type 2 diabetes.
Understandably, Amanda questioned whether the stress of the blood test might have pushed her fasting level higher than normal. And she’s right to raise that concern.
Morning blood sugar levels can be affected by short-term stress, sleep, or illness. In this situation, where results don’t match and there’s no clear reason for the diagnosis, it’s generally recommended to confirm with a second test on a different day.
While Amanda’s doctor may have had other clinical reasons to make the call, repeating the test could offer a clearer picture and more confidence in the result.
Conclusion
These real-life cases highlight the complexity behind some diagnoses, and why it’s so important to understand what each test means and how to interpret results in context.
Most importantly, remember that a diagnosis is not a verdict — it’s a starting point. Whether you’ve just received a diagnosis or are working to prevent type 2 diabetes, understanding your test results gives you power. And we’re here to help you make sense of it all, every step of the way.
Inside our members site, we often help our members determine their test results, via our monthly member check ins, or during your quarterly health update, where you can submit your test results for review. Change your life and join us as a member today.
Transcript
Click Here To View
Dr Jedha, Host
Hello there wonderful people and thanks for joining me. Today’s episode is one I know many of you have questions about: How is diabetes actually diagnosed? This is a very fundamental episode inspired by the numerous questions we get about diagnosis and the confusion around those numbers.
It’s not always straightforward. I’ve heard from many of you who feel surprised or even blindsided by a diagnosis, especially when your numbers don’t seem to match. So in this episode, we’ll walk through the official medical guidelines from the American Diabetes Association — what tests are used, what the cut-offs are, and why two people can get very different results depending on which test is done. For those of you outside the US, the same diagnostic criteria apply but the diagnostic numbers may be slightly different, so what we’re speaking about today will be applicable to you no matter where you’re located.
Plus, we’ll go over two straightforward examples and cover two real questions from listeners — both of whom were left wondering how they went from normal to diabetic, seemingly overnight. These will be great case studies to demonstrate the complexities and confusions of diagnosis.
02:30
Let’s start by breaking down the diagnostic criteria…the tests and numbers that diagnose diabetes.
There are four different tests that can be used, a hemoglobin A1c test, a fasting blood glucose test, an oral glucose tolerance test, or a random blood glucose test. A diagnosis can be made if any one of these tests reaches the threshold — and most often, it’s either confirmed on a second day or backed up by another abnormal test done at the same time.
Let’s look at each one of these tests more closely. Before we go into the actual numbers, I want to reemphasize that these numbers can be slightly different depending where you live. This is really frustrating as ideally these should all be the same, but they aren’t so I will make sure to include the different ranges for the US, Canada, Australia and UK – just so you have those baseline numbers because I know we have listeners from all over the world.
03:35
Okay, so the first test that can be used to diagnose diabetes is a hemoglobin A1c test, also known as HbA1c or A1c. This measures your average blood sugar over the past few months. Type 2 diabetes is diagnosed when A1c is 6.5% or higher, which is 48 mmol/mol – that’s the same all over the world. In the US, prediabetes is diagnosed when A1c is between 5.7% and 6.4%, which is 39–47 mmol/mol, and below 5.7% (below 39) is considered normal. In most other places across the world, prediabetes is diagnosed when A1c levels are 6.0 to 6.4% or 42 – 46 mmol/mol, and less than 6.0% or 42 is considered a normal A1c.
04:48
The second type of test is a Fasting Blood Glucose test, which is taken after at least 8 hours without food. This test measures whether your fasting blood glucose is normal or impaired. Type 2 diabetes is diagnosed when fasting glucose is 126 mg/dL or higher, that’s 7.0 mmol/L or higher – that’s the same all over the world. In the US, prediabetes is diagnosed with fasting glucose of 100 to 125 and below 100 is normal. For most other places in the world, prediabetes is diagnosed with a fasting glucose of 6.1 – 6.9, while 6.0 or below is considered normal. But something to note here is that if your fasting glucose levels are between 5.6 to 6.0, this can still indicate prediabetes might be possible, especially if you have other risk factors. So the best course of action here is that if your fasting levels are considered normal but come back at 5.6 to 6.0, take action now to avoid a prediabetes diagnosis and to protect your long term health!
06:10
Another test is the Oral Glucose Tolerance Test, or OGTT. This one involves drinking a sugary drink containing 75 grams of glucose and testing your blood sugar 2 hours later. This test measures whether your tolerance of carbohydrates is normal or impaired. Type 2 diabetes is diagnosed if the 2-hour result is 200 mg/dL or higher, that’s 11.1 mmol/L or higher. Prediabetes is diagnosed with an OGTT result of 140 to 199 or 7.8 to 11.0. Below 140 or 7.8 is normal. These numbers are the same all over the world.
07:02
The other test that is sometimes used is a Random Blood Glucose test. If you’re showing symptoms of high blood sugar — things like excessive thirst, excessive urination, fatigue, or blurry vision — a random blood sugar test might be conducted and if the results come back at 200 or 11.1 or higher, this can confirm a type 2 diabetes diagnosis. A random blood glucose test is not used to diagnose prediabetes.
If you’re still confused by these diagnostic numbers, head to the show notes for episode 86 and we’ll leave a table of the numbers. It can really help to see them so you can review them in reference.
08:29
Next I want to share two straightforward examples of diabetes being diagnosed. Then I’ve got two specific case studies to share, and we’ll delve deeper into answering the question about whether a test can be inaccurate.
Case 1: The Annual Check-Up Surprise
Emma is 59 and went in for her routine annual check-up. She wasn’t experiencing any symptoms, but her doctor decided to run some standard blood work — including an HbA1c and fasting blood glucose.
Her fasting glucose came back at 132 mg/dL (7.3 mmol/L) and her A1c was 6.7%. Since two separate markers were above the diagnostic thresholds, Emma was diagnosed with type 2 diabetes that day — even though she felt fine.
This is a classic example of how type 2 is often diagnosed: through routine testing, sometimes before any symptoms even appear. Often people don’t even know they have diabetes, since diabetes often does display zero symptoms. And it’s common for people to be diagnosed when they take a visit to their doctor for an entirely different reason.
09:54
Case 2: Symptoms Lead to Testing
Now let’s take John. He’s 49 and had been feeling unusually thirsty, getting up several times at night to urinate, and feeling more tired than usual. He made an appointment with his doctor to talk about it.
His doctor ran a random blood glucose test while he was in the office — and it came back at 228 (12.6). Because he had clear symptoms and a glucose level over 200 (over 11.1), that alone was enough for a diagnosis of type 2 diabetes.
In case number one, Emma had no symptoms, she was what’s called asymptomatic, but she had 2 different types of tests that come back above normal and in the type 2 diabetes range, so she was confirmed as diagnosed type 2 diabetes on the spot.
In case number two, John was symptomatic, displaying symptoms of diabetes and his random glucose test came back above normal and in the type 2 diabetes range, so he was confirmed as diagnosed type 2 diabetes on the spot.
Let me just explain these two criteria that can be used by a doctor to determine how to proceed with your diagnosis – symptomatic and asymptomatic.
If you’re symptomatic, it means you’re experiencing signs that something might be wrong with your blood sugar. These could include excessive thirst, frequent urination, blurred vision, unexplained weight loss, or constant fatigue. If those symptoms are present and your blood sugar is high, like in John’s case with the random test, then that alone can be enough for a diagnosis. Or if you were symptomatic and your A1c, OGTT or fasting glucose came back abnormal, you could also be diagnosed with type 2 diabetes off one abnormal test alone.
But if you’re asymptomatic — meaning you feel fine and don’t have any of those obvious signs — then the guidelines recommend a more cautious approach. In those cases, at least two abnormal test results on separate occasions are typically required to confirm prediabetes or type 2 diabetes.
Keep these things in mind as we discuss our next two case studies.
12:37
Taryn sent in a message saying:
“I am interested to know more about the role of HBA1C and oral glucose tolerance test as I’ve been diagnosed with Type 2 Diabetes. I love my doctor she’s amazing but I left her office the first day with a script for metformin and the plan was to return for a longer consultation. Before the next appointment I had started my own research and one of the first things I found was your podcast which has been extremely informative. My HBA1C in February was 6.0 which would indicate prediabetes but my oral glucose tolerance test indicates I have Type 2 Diabetes. I’m frustrated as it’s like I’ve skipped prediabetes and gone straight to Type 2 – a label that will stick forever which means I have no chance of turning around the diagnosis. My doctor says we’ve caught it early…In my next appointment I told her I hadn’t started the metformin as my HBA1c at 6 wasn’t too bad so I would like to try and turn it around with diet and exercise first. I guess I’m just interested in your views on what role the HBA1C and OGTT play in diagnosis.”
So Taryn was given a diagnosis of type 2 diabetes, and she was feeling frustrated about it because of the discrepancies in the results. On her first test, her A1c test was 6.0 – in the prediabetes range, but her oral glucose tolerance test was in the type 2 diabetes range. Both of these tests indicate an issue with glucose metabolism, because one result is prediabetic, one is diabetic, so how does the doctor choose?
The A1c test measures your average blood sugar over about three months. But it can sometimes miss sharp spikes after meals, especially in the earlier stages of glucose dysregulation. A1c has a lower sensitivity than testing your 2-hr postprandial glucose. Whereas the OGTT — where you drink a sugary solution and measure blood sugar two hours later — is really good at detecting those post-meal highs, which can be a first sign that your body’s struggling to manage glucose. So, your doctor is right Taryn, by saying that you have caught it early. Early enough that your A1c levels aren’t too high, but your body is showing you it’s struggling with carbohydrate metabolism.
According to the guidelines, if a person has two tests that indicate diabetes, a diagnosis is confirmed. As for which diagnosis, well, that could depend. If you were symptomatic, had those other symptoms like excessive thirst, frequent urination, blurred vision, unexplained weight loss, or constant fatigue, then the doctor could confirm the type 2 diabetes diagnosis off one single oral glucose tolerance test.
But in Taryn’s case, even if she didn’t have these symptoms, because of her high A1c in the prediabetes range, the single oral glucose tolerance test does in fact confirm this as a type 2 diabetes diagnosis, since essentially the A1c test is indicating a clear symptom of diabetes – high blood glucose. If Taryn didn’t have the elevated A1c, if it was only the oral glucose test that came back abnormal, then the doctor would have ordered another oral glucose tolerance test on another day to confirm the diagnosis.
Of course Taryn, if your doctor does subsequent tests within a short timeframe and your oral test is not in the type 2 diabetes range, then you’d have to have a discussion about the diagnosis. But for now, while it may seem frustrating, your doctor has diagnosed you accurately based on the guidelines. It has been caught early and you have one very good indicator to work on, 2-hour postmeal glucose and that is very easy to lower via diet and exercise, often without medication.
17:41
Our next case study comes from Amanda. She said:
“l am someone who suffers from bad health anxiety and whenever l am coming up to blood work l get myself worked up. My last blood test recently had my fasting blood glucose at 7 (that’s 126) but my HbA1c at 5.6. My doctor still said l now have type 2 diabetes and l’m not sure what to believe as l know stress can affect fasting blood glucose levels. But she just brushed me off when l said my HbA1c is more indicative of my actual blood sugars level overall. Very confusing.”
Firstly, thank you for being so open Amanda. I want to say clearly — your feelings are completely valid. When you’re already anxious, and you receive what feels like a conflicting message from your doctor, it’s incredibly unsettling. Let’s unpack what could be happening here.
So in Amanda’s case we see another instance where A1c levels are normal but this time it’s a fasting blood glucose test that is high at 7.0, which is 126 and this is considered within the type 2 diabetes diagnostic range.
The fasting blood glucose test is just a snapshot — a single moment in time. And yes, it can be influenced by stress. When you’re anxious, your body releases hormones like cortisol and adrenaline, which naturally raise your blood sugar. So it’s entirely possible that your fasting level on the day of your blood test was artificially elevated by that stress.
Now, your A1c of 5.6 suggests your average blood sugar over the past few months is still in the normal range. According to guidelines, that wouldn’t meet the threshold for type 2 diabetes. In fact, it’s below even the prediabetes range, it is perfectly normal.
So in cases like this — where there’s a clear mismatch between A1c and fasting glucose, where there is a clear discrepancy in the test results, and particularly when there’s a plausible reason for the elevated fasting result — it’s usually good clinical practice to repeat the test or look at other markers before making a firm diagnosis. But, something to consider is that it is quite elevated—it’s not just marginally elevated. Another thing is, your doctor has your full medical history so it may be the case that they consider you a symptomatic person, a person who has symptoms of high blood sugar—such as excessive thirst, frequent urination, blurred vision, unexplained weight loss, or constant fatigue—if that were the case then they can confirm a type 2 diabetes diagnosis off one single elevated fasting blood glucose or random blood glucose test; or there may have been another reason why they reached this conclusion so readily. Amanda would need to discuss those specifics with her doctor.
Theoretically speaking, if you have one or multiple symptoms of diabetes, it could suggest rapidly evolving diabetes even though A1c levels are normal. But, according to the guidelines, unless there are clear clinical symptoms of high blood sugar or high blood sugar crisis, for example being submitted to the emergency room, then TWO abnormal screening results are required – results can either be tested at the same time, for example a high A1c and FBG, or at two different time points. In Amanda’s case, if there was no valid reason for the diagnosis, then a separate fasting blood glucose test should be done on a separate day within a fairly short timeframe.
Something to note is that fasting blood glucose is often one of the very first blood glucose measures to rise. If you have caught this higher early, then it’s providing you with insight into how well your body is managing blood sugar overnight — especially liver glucose output and indicating your baseline insulin sensitivity and metabolic function. So if it is the only measure that is high, it’s giving you an early sign that some changes are occurring in terms of insulin sensitivity and insulin resistance and your metabolism. That’s powerful because you can work on these things.
But of course, if you wanted to discuss the specific diagnosis with your doctor, one proactive strategy you could take here is to monitor your own blood sugar at home — especially your fasting levels and post-meal responses — over a couple of weeks. You can then take an assessment yourself, looking at patterns, and note down those numbers on paper. That can give you and your doctor a more complete picture before settling on a diagnosis.
23:36
As you’ve probably become aware of from our different case studies, the diagnostic tests reflect different aspects of glucose metabolism.
- A1c – based on an average measure of glucose on the blood over a 3-month period
- IFG – based on the FBG test
- IGT – based on the 2-h PG test
- And 2h PG – based on how your body manages a glucose load
Can tests be inaccurate? Absolutely yes they can. While it’s not common, it is a possibility.
HbA1c tests can be false low if a person has substantial blood loss, renal failure, in pregnancy, in relation to vitamin E levels, in the presence of certain types of anemia, among other things. HbA1c tests can be false high in people with B12, iron or folate deficiency, abnormal spleen function, blood transfusion or with random hemoglobin variants.
Fasting blood glucose can be thrown off by acute stress, a bad night’s sleep, illness, or even what you ate the night before.
OGTT results can vary depending on how physically active or carb-depleted you were in the days leading up to the test.
There can be discrepancies in results, and it will come down to the other information your doctor has. That’s why the guidelines recommend confirmation — either repeating the same test or using a second test — especially in people who are asymptomatic. Having a second test, requesting one, is not just a safeguard; it’s a reminder that these tests give us information, but they’re not absolute truth in isolation.
So if something feels off — trust your gut, ask questions, and don’t be afraid to request a second look. Your health deserves clarity, not confusion.
And remember: a diagnosis is not a verdict. It’s a guidepost. No matter what label you feel you may have been given, your health is something you can influence. And you’re already doing that by asking questions, learning more, and staying engaged in your care.
We know from over a decade of experience that no matter how long the diagnosis, people can turn this around. So don’t let the label define you. What you do from here matters more than the name in your file.
Remember, we provide an amazing service to help people achieve normal A1c, lose weight and get off meds and real support to help you overcome confusions and gain clarity, so be sure to head down to our website to learn more about how we can support you.
Thanks for listening and I hope it’s provided some clarity and confirmation about how diabetes is diagnosed, and if you know it will help someone else please share.
That’s all from me today.
Dr Jedha, over and out.
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