On This Page – Quick Medical Summary
Where you are right now, and what this page answers
If a lab result came back higher than you expected and someone asked you to come back for a second test, you are in the right place. Most people arrive here in one of four situations, and each one needs a different part of this page.
You have one high result and a second test booked. Start with the next section, then read what a second result can and cannot change.
You already have two results and they disagree. Skip to the section on discordant results — that question has a specific answer in current guidance.
You are reading someone else’s result — a parent’s, a partner’s — and you are the one making the appointment. The questions in the “between the two tests” section are written to be asked by whoever is in the room.
You already have a confirmed diagnosis. This page will not help you, because your A1C is now a monitoring test; the pillar guide on how to read an A1C result and its honest margin is the better starting point.
You have one high result and a second test booked
A repeat test is not a sign that anyone doubts you, and it is not a sign that the first result was a mistake. It is the ordinary next step. The National Institute of Diabetes and Digestive and Kidney Diseases puts it plainly: usually, a doctor will use a second test to confirm that a person has diabetes.
What this page does is tell you what that second test decides. That turns out to be narrower than most people expect, and in one specific way it is stricter.
You already have two results and they disagree
If your A1C and a glucose test point in different directions, there is a documented rule for what happens next, and it is not “the lower one wins.” It is also not a sign that either lab made an error.
That rule sits in the section on discordant results below, along with what it means when a fasting plasma glucose comes back normal after a high A1C.
ℹ️ Medical Disclaimer: This article is general health education about a diagnostic blood test: it does not diagnose diabetes or prediabetes, does not recommend or adjust any medication, does not tell you whether to have or delay a test, and does not describe what any insurance plan will cover for you. Diagnosis, medication decisions, test timing and coverage questions all belong with your own clinician and your own plan. If you have a result you are worried about, contact the clinician who ordered it and ask what the next step is for you specifically.
Why one high A1C usually gets a second test
A single abnormal diagnostic test result usually is not enough to diagnose diabetes on its own. Under current guidance a diagnosis normally needs two abnormal results, and that is why your clinician asked you back — not because your first result looked unusual, but because confirmation is the standard step for everyone.
The reason is not that A1C tests are unreliable. It is that a diagnosis is a permanent label attached to a measurement, and measurements move.
The line under the chart that most people never read
Almost every A1C chart on the internet carries a footnote, and almost nobody reads it. The NIDDK’s A1C test page, last reviewed in April 2018, prints it directly beneath its diagnostic table: any test used to diagnose diabetes requires confirmation with a second measurement, unless there are clear symptoms of diabetes.
That single line is the whole rule. It is also why a chart alone cannot tell you whether you have diabetes — the chart tells you which band a number falls in, and the footnote tells you that one number in a band is not a diagnosis. If you want the bands themselves, they are set out in the A1C chart and what each range means.
MedlinePlus says the same thing in patient language: providers often use more than one test to diagnose diabetes, so a higher-than-normal result may be followed by another A1C or a different diabetes test.
A prediabetes result gets confirmed too
This is the part that almost never gets printed. NIDDK’s instruction covers both bands: if you do not have symptoms and the A1C test shows diabetes or prediabetes, you should have a repeat test on a different day, using the A1C test or one of the other diabetes tests, to confirm the finding.
So a result in the prediabetes range is not automatically settled either. If your result sits in that band and you have been told to come back, that is the same rule being applied, and what doctors check next after a prediabetes-range A1C covers what usually follows.
Why a lab result is not a single fixed number
Lab results vary from day to day and from test to test. NIDDK lists three ordinary reasons: your own glucose levels move, red blood cell conditions can shift an A1C, and small changes in temperature, equipment or sample handling affect any measurement.
🔬 How It Works: An A1C measures the percentage of your hemoglobin that has glucose attached to it, built up over the life of your red blood cells. Because that is a long-run average rather than a snapshot, it moves less between tests than a fasting glucose does — NIDDK notes that A1C is less affected by short-term changes than fasting or tolerance testing. It still moves, which is exactly why a second measurement exists.
None of that makes the first result meaningless. It makes a single result an estimate with a margin, which is a different thing, and the pillar guide explains that margin in detail. If your first result came back at or above the diagnostic line, what happens after an A1C of 6.5 or higher walks through the wider picture.
What a second result changes, and what it does not
A second result can come back lower than the first and still confirm a diagnosis of diabetes. What decides the outcome is not whether the two numbers match, and not whether the second one improved — it is whether both results sit above the diagnostic line.
That is the part almost nobody is told, and it is why so many people expect a verdict the second appointment is not going to deliver.
A lower second result can still confirm it
The American Diabetes Association’s Standards of Care in Diabetes—2026, Section 2, works the example out explicitly. If an A1C is 7.0% and a repeat result comes back at 6.8%, the diagnosis of diabetes is confirmed.
Both values sit above the diagnostic line, so the fall between them changes nothing: the second test is a confirmation, not a rematch.
📊 Clinical Data Point: In the American Diabetes Association’s Standards of Care in Diabetes—2026, Section 2, the worked example for confirming diabetes is an A1C of 7.0% followed by a repeat of 6.8% — a lower second result that still confirms the diagnosis, because both values sit above the diagnostic threshold. That is not a sign the test is unreliable, and NIDDK states the other half of it directly: health care professionals understand these variations and repeat lab tests for confirmation, and because diabetes develops over time they can tell when overall glucose levels are becoming too high even with variation between results.
Source: American Diabetes Association, Standards of Care in Diabetes—2026, Section 2; National Institute of Diabetes and Digestive and Kidney Diseases, The A1C Test & Diabetes (last reviewed April 2018).
What the two results are actually compared against
Each result is compared against the diagnostic threshold on its own, not against the other, and no rule says the second must match or exceed the first. This is also why a small movement between two results is not a finding in itself. A single A1C is an estimate with a margin around it, which the pillar guide covers in detail — and understanding why one A1C result is a range rather than one fixed number is the single most useful thing to read before your second appointment.
The table below sets out what current guidance says happens in each of the four situations people actually find themselves in.
| Your situation | What current guidance says happens | Key clinical detail |
|---|---|---|
| Second result is higher than the first, both above the line | Diagnosis confirmed | Two abnormal results are what the criterion asks for; the direction of change is not part of it |
| Second result is lower than the first, both above the line | Diagnosis confirmed | This is the ADA’s own worked example — a fall from 7.0% to 6.8% still confirms |
| Second result falls below the diagnostic line | The two results are discordant; the result above the cut point is repeated | The diagnosis is then made on that confirmatory test, not on whichever result you prefer |
| A different test (such as a fasting glucose) disagrees with the A1C | The result above the cut point is repeated, with attention to anything that could affect either measurement | Meeting the criterion on one test and not the other does not cancel the diagnosis |
Source: American Diabetes Association, Standards of Care in Diabetes—2026, Section 2. This table describes what current guidance instructs clinicians to do; it does not tell you what your own clinician will decide for you.
What a confirmed result does not say about you
A confirmed diagnosis is a measurement crossing a line twice. It is not a verdict on how you have eaten, how much you have moved, or how seriously you have taken your health.
It also is not a statement about what happens next, which depends on the type, your other results and decisions you have not made yet. NIDDK’s guide to the tests used to diagnose diabetes is the plainest federal summary of what each test does and does not establish.
🩺 Physician Note: A common point of confusion is the belief that the second test overrides the first. Current guidance does not work that way — the two results are read together against the same threshold, and where they disagree there is a specific instruction for which one gets repeated. If you are unsure, ask the clinician who ordered the test directly: “which of my two results are you using to make the call, and does either one need repeating?”
When your A1C and a glucose test disagree
When two different tests point in different directions, current guidance is specific about what happens: the result that is above the diagnostic cut point is the one that gets repeated. The diagnosis is then made on the basis of that confirmatory screening test.
A normal result on the other test does not, by itself, close the question.
The result above the line is the one repeated
The ADA’s Standards of Care in Diabetes—2026, Section 2, states it directly. Where an individual has discordant results from two different tests, the test result above the diagnostic cut point should be repeated, with careful consideration of factors that may affect the measured A1C or glucose level.
Those factors are real and worth raising with your clinician, and what makes an A1C result accurate enough to act on covers which conditions and testing situations genuinely change an A1C.
A normal fasting glucose does not cancel a high A1C
The same section gives the case explicitly: where someone meets the diagnostic criterion on A1C across two results but not on fasting plasma glucose, that person should nevertheless be considered to have diabetes.
This is the opposite of what most people assume, and it is the reason a normal fasting number after a high A1C is not the all-clear it feels like. The two tests are not interchangeable instruments, and how an A1C and a fasting glucose differ as measurements explains why their results can legitimately part ways.
Why two tests can point different ways
NIDDK is direct about this: in some people a blood glucose test may show diabetes when an A1C does not, and the reverse also happens. Because of those differences, health care professionals repeat tests before making a diagnosis.
NIDDK offers one further explanation that is genuinely reassuring rather than alarming — people with differing test results may be at an early stage, when glucose has not yet risen high enough to show on every test. The full mechanism is set out in what a normal A1C level actually confirms, which is the better place to read about why two tests disagree at all.
✅ Patient Action: Before you leave your next appointment, ask the clinician who ordered the test: “my two results disagree — which one are you repeating, and is there anything about me that could be affecting the A1C specifically?” Anemia, other red blood cell conditions, kidney failure and liver disease can all affect how accurate an A1C is for diagnosis, and MedlinePlus notes that a different test may be recommended in those cases.
When one result is enough, and when you wait
There are two exceptions to the confirm-it-twice rule and they point in opposite directions: one means the diagnosis is not waiting for a second test, the other means a planned wait is the recommendation rather than a delay. Knowing which applies to you matters more than knowing the general rule.
When symptoms mean the diagnosis is not waiting
The confirmation requirement carries an exception written into it. NIDDK’s footnote ends with the qualifier: unless there are clear symptoms of diabetes.
The ADA’s Standards of Care in Diabetes—2026, Section 2, describes the same exception in clinical terms — where someone has classic symptoms of hyperglycemia or presents in a hyperglycemic crisis alongside a random plasma glucose above the diagnostic level, a single measurement is sufficient and confirmatory testing is not required first.
⚠️ Clinical Warning: If you have a high A1C result and you are currently experiencing symptoms such as intense thirst, urinating far more than usual, unexplained weight loss or blurred vision, do not wait for a scheduled repeat test. Contact the clinician who ordered your result, or an urgent care service, and say that you have an elevated A1C together with those symptoms. In that situation the rule about waiting for a second test does not apply to you.
When your result sits close to the line
The other exception runs the other way. The same ADA section advises that results close to the diagnostic threshold should prompt the clinician to educate the person about the possible onset of symptoms of high blood glucose, and to repeat the test in three to six months.
Both halves of that travel together. The wait is not a dismissal, and it comes attached to knowing which symptoms would change the plan before the repeat is due.
How soon the second test should happen
Current guidance does not put a number of days on it. Where two samples are taken at different time points, the ADA’s 2026 Standards say the second test — which may be a repeat of the first test or a different test — should be performed in a timely manner; NIDDK’s wording is a repeat test on a different day.
Those are not the same as a deadline, and no source states one. Once a diagnosis is settled, the schedule changes to an ongoing one, and how often an A1C should be checked after that covers the intervals that then apply.
The CDC’s A1C test page, which displays a date of 15 May 2024, sets out the re-testing guidance that follows a normal or prediabetes-range result.
What to do in the weeks between the two tests
The gap between the two tests is usually the hardest part, because there is nothing to decide and nothing yet to act on. There are three things worth doing and one worth deliberately not doing — and none of them will change your result, which is the point.
What to ask before you leave the appointment
The most useful questions are short, specific and answerable in under a minute each: which test is being repeated and why that one, whether anything in your history could affect an A1C specifically, and what you should watch for that would mean coming back sooner. There is one more worth asking, now that you know it has a documented answer — what happens if the two results disagree.
✅ Patient Action: Take four questions to the clinician who ordered your test — not to a pharmacy or a walk-in service: which test are you repeating and why that one; is there anything about me, such as anemia, another red blood cell condition, kidney failure or liver disease, that could affect my A1C; what symptoms would mean I should come back before the repeat; and if the two results disagree, which one will you act on. Writing them down beforehand is worth more than remembering them.
Whether you need to fast for the repeat
An A1C itself does not require fasting — NIDDK is explicit that blood can be drawn for it at any time of day. The complication is that a repeat visit often collects more than one test.
If a fasting plasma glucose is being drawn at the same appointment, that one does have a preparation requirement, and whether you need to fast for an A1C test sets out the conditional answer properly. Ask which tests are on the order before you assume either way.
The one thing not to change before the second test
This is the honest and slightly uncomfortable part. A sudden, intense effort in the weeks before a repeat test does not make the underlying situation better, and it does make the second result harder to interpret — the two measurements are supposed to describe the same period, and one that describes an unusual few weeks tells your clinician less.
That is a point about timing, not about whether change is worth making. If you want to make changes, they are worth making — the argument is for making them as part of a plan your clinician knows about, rather than as a two-week attempt to move a number.
One thing in particular should not change on your own initiative. MedlinePlus notes that certain medicines, including opioids and some HIV medicines, can affect A1C results, and its instruction is to tell your provider about everything you take — but not to stop taking any medicine unless your provider tells you to.
Repeat testing is ordinary across all of blood work, not a diabetes-specific ritual, and when a blood test result gets repeated covers the same question for a different panel.
What a confirmatory test cannot do for you
Two abnormal results establish that a person has diabetes. They do not establish which kind, and they cannot be assembled from just any two numbers you happen to have — both limits are worth knowing before the second appointment rather than after it.
It confirms diabetes, not which type
NIDDK states it plainly: even though these tests can confirm that you have diabetes, they cannot identify what type you have — type 1, type 2, or a rare form called monogenic diabetes. Treatment can depend on the type, so knowing which one is important.
There is a further limit in the same direction. MedlinePlus’s A1C lab-test page, last updated 20 May 2025, states that the A1C test is not used to diagnose type 1 diabetes, and separately that it is not used to diagnose gestational diabetes. What happens after confirmation, including how the type is established, is covered in this cluster’s guide to a result at or above the diagnostic line.
A home kit or a pharmacy result cannot be the second test
We do not recommend or link to any home A1C product on this page, and the reason comes from our own cited sources rather than from a preference. NIDDK states that blood samples analyzed in a doctor’s office or clinic — point-of-care tests — should not be used for diagnosis, and that over-the-counter blood testing equipment cannot diagnose diabetes. For diagnosis, NIDDK describes a sample taken from a vein and sent to a lab using an NGSP-certified method; MedlinePlus describes the same venous draw.
Recommending a product that our own sources say should not be used for this purpose would not be honest, and it would be a particularly bad thing to do on a page read by someone deciding whether they can skip a confirming draw.
⚠️ Clinical Warning: A fingerstick result from a health fair, a pharmacy screening event or a home kit is not one of the two results a diagnosis is built from. If a screening result outside a clinical setting is what brought you here, treat it as a prompt to get tested properly rather than as a first result already in hand — and say where it came from when you book. The same distinction between a walk-in screening result and a diagnostic lab draw applies across blood work, and it is set out for another panel in what a walk-in cholesterol test can and cannot do.
🩺 Physician Note: The point here is regulatory rather than a judgment about device quality. A point-of-care result is not admissible as one of the two results a diagnosis requires, which is a different claim from saying the device is inaccurate. If you have a result from outside a clinical lab, ask your clinician whether it counts toward anything or whether the sequence starts again.
Questions people ask about the second A1C test
1. Does one high A1C mean I have diabetes?
Usually not on its own. Current guidance is that any test used to diagnose diabetes requires confirmation with a second measurement, unless clear symptoms of diabetes are present, which is why a single high A1C is normally followed by a repeat. Ask the clinician who ordered your test which second test they are planning and when.
2. Why do I need a second A1C test?
Because a diagnosis is permanent and a single measurement is an estimate. Lab results vary from day to day and from test to test for ordinary reasons, so an a1c confirmatory test exists to make sure a diagnosis rests on two abnormal results rather than one. Your clinician can explain which second test suits your situation.
3. Can the second test be lower than the first and still confirm it?
Yes. In the American Diabetes Association’s 2026 Standards of Care, the worked example for confirming diabetes is an A1C of 7.0% followed by a repeat of 6.8%, and the diagnosis is confirmed because both values sit above the diagnostic line. The two results are compared against the threshold, not against each other.
4. Does the second test have to be another A1C?
No. NIDDK’s instruction is a repeat test on a different day using the A1C test or one of the other diabetes tests, and MedlinePlus notes the second test is usually either a fasting blood glucose test or an oral glucose tolerance test. Which one is chosen is a clinical decision worth asking your clinician about.
5. How soon should the second test be done?
No source states a specific number of days. Where two samples are taken at different time points, the ADA’s 2026 Standards say the second test should be performed in a timely manner, and NIDDK’s wording is a repeat on a different day. Ask the clinician who ordered your first result what interval they want.
6. What if my A1C is high but my fasting glucose is normal?
That is a discordant result, and current guidance has a specific instruction: the result above the diagnostic cut point is the one repeated, and the diagnosis is made on that confirmatory test. Meeting the criterion on A1C across two results but not on fasting glucose does not cancel the finding. Raise the disagreement directly with your clinician.
7. When is one test enough to diagnose diabetes?
When clear symptoms are present. The confirmation requirement carries an explicit exception for clear symptoms of diabetes, and current guidance treats classic symptoms of high blood glucose alongside a random plasma glucose above the diagnostic level as sufficient on its own. If you have a high result and those symptoms now, contact your clinician or urgent care rather than waiting.
8. Does a prediabetes A1C get confirmed too?
Yes, and this is rarely printed. NIDDK’s instruction covers both bands: if you have no symptoms and the A1C test shows diabetes or prediabetes, you should have a repeat test on a different day to confirm the finding. So a result in the prediabetes range being repeated is the same rule being applied, not a sign of extra concern.
9. Should I change anything before the second test?
A sudden intense effort in the weeks beforehand makes the second result harder to interpret without improving the underlying situation, so changes are better made as part of a plan your clinician knows about. MedlinePlus is explicit on medicines: tell your provider about everything you take, but do not stop any medicine unless your provider tells you to.
10. Can a home A1C kit or a pharmacy result count as the second test?
No. NIDDK states that point-of-care samples analyzed in a doctor’s office or clinic should not be used for diagnosis, and that over-the-counter blood testing equipment cannot diagnose diabetes; for diagnosis, a sample is drawn from a vein and sent to a lab using an NGSP-certified method. Tell your clinician where any screening result came from, because it changes whether the testing sequence starts again.
11. What does the second test not tell me?
It does not tell you which type of diabetes you have. NIDDK states that these tests can confirm diabetes but cannot identify whether it is type 1, type 2 or a rare monogenic form, and that knowing the type matters because treatment can depend on it. Ask your clinician how the type will be established in your case.
What to take to your next appointment
Three things are worth carrying into the room. A second result does not have to be higher, or even match, to confirm a diagnosis — both results are read against the same line. If the two tests disagree, the one above the line is the one repeated, and the diagnosis is made on that confirmatory test.
And the second test settles less than it feels like it should: it establishes diabetes, not which type, and it cannot be assembled from a screening result taken outside a clinical lab.
The most useful thing you can do before the repeat is decide what to ask. Which test is being repeated and why, whether anything about you could affect an A1C specifically, what symptoms would mean coming back sooner, and which result your clinician will act on if the two disagree. Those four questions fit in a short appointment, and they are answerable.
If the wider picture is what you need, the pillar guide on reading an A1C result and its honest margin covers the margin around a single number, and this cluster’s guide to a result at or above the diagnostic line covers the ground beyond confirmation.
About this content
How this article was put together: researched from recognised health sources, drafted with the help of AI tools, and edited by hand, with sources linked throughout.
Sameer Patel is the founder and editor of My Medicine Advisor. He is not a doctor or medical professional — before starting this site he worked in banking,…
Medical disclaimer
The content on MyMedicineAdvisor is provided for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Health information on this website should not be used to diagnose, treat, cure, or prevent any condition without guidance from a qualified healthcare professional. Always seek the advice of your doctor, physician, or another licensed healthcare provider with any questions you may have regarding a medical condition, symptoms, medications, or treatment decisions.
