The three prediabetes blood tests and their ranges
NIDDK lists three tests, each with its own prediabetes range. Any one is enough to flag prediabetes, and doctors usually confirm a result with a second test. HbA1c needs no fasting and reflects roughly the last three months; fasting glucose is a snapshot of one morning; the oral glucose tolerance test (OGTT) measures glucose 2 hours after a sugary drink and is the most sensitive.
Source: NIDDK diagnostic table. Diabetes starts at 126 mg/dL fasting and 200 mg/dL on the 2-hour OGTT.
| Marker | Why it matters | What a result suggests | On SiPhox |
|---|---|---|---|
| HbA1c | Average blood sugar over about 3 months, no fasting | 5.7% to 6.4% is prediabetes; 6.5% or more is the diabetes range | Longevity, Heart & Metabolic, Ultimate 360, GLP |
| Fasting glucose | One-morning snapshot after 8 hours without food | 100 to 125 mg/dL is prediabetes; 126 or more is the diabetes range | Not on SiPhox |
| 2-hour OGTT | Most sensitive; catches after-meal spikes | 140 to 199 mg/dL is prediabetes | Not on SiPhox |
| Fasting insulin and HOMA-IR | Show insulin resistance before glucose rises | High insulin with normal glucose suggests the body is compensating | Not on SiPhox |
| C-peptide | Tracks how much insulin the pancreas makes | High values fit insulin resistance; interpret with glucose | Longevity, Heart & Metabolic, Ultimate 360, GLP |
| Triglyceride:HDL ratio | Cheap marker of insulin resistance | Higher ratios travel with insulin resistance | Longevity, Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| ALT | Fatty liver often accompanies prediabetes | Raised ALT needs a cause; weight loss often lowers it | Heart & Metabolic, Thyroid Focus, Ultimate 360, GLP |
| ApoB | Prediabetes raises heart risk; ApoB and LDL often disagree here | High ApoB with normal LDL is common in insulin resistance | Longevity, Heart & Metabolic, Ultimate 360, GLP |
Which prediabetes test to choose
| Test | Fasting? | Strength | Weakness |
|---|---|---|---|
| HbA1c | No | Any time of day; reflects about 3 months; works from a home sample | Skewed by iron deficiency, blood loss, kidney or liver disease and some hemoglobin variants (NIDDK) |
| Fasting glucose | 8 hours | Cheap, widely available | Day-to-day variation; unreliable from capillary samples mailed to a lab |
| OGTT | 8 hours, then 2 hours in the lab | Most sensitive; preferred in pregnancy and for women with PCOS at higher risk | Takes a morning; must be done in a clinic |
NIDDK notes a falsely high A1C can occur with iron-deficiency anemia, and that people of African, Mediterranean or Southeast Asian descent may carry hemoglobin variants that interfere with some A1C tests. If your A1C and glucose disagree, ask your doctor which to trust. SiPhox reports HbA1c with an estimated average glucose (eAG), calculated from A1C using the ADAG formula, so an A1C of 5.7% reads as an eAG of about 117 mg/dL; eAG is a translation of A1C, not a separate glucose measurement. Our at-home A1C test guide compares meters and mail-in kits.
Who should get a prediabetes blood test
- Adults 35 to 70 with overweight or obesity: the US Preventive Services Task Force recommends screening (grade B). Its 2021 statement estimated that 34.5% of US adults meet the criteria for prediabetes and 13% have diabetes.
- Anyone with risk factors such as a parent or sibling with type 2 diabetes, past gestational diabetes, PCOS or high blood pressure. The CDC says more than 2 in 5 American adults have prediabetes.
- People already told they have prediabetes: retest at least yearly, as the ADA advises, to catch progression early.
Why it matters: in the Diabetes Prevention Program, a lifestyle program cut the incidence of type 2 diabetes by 58% and metformin by 31% compared with placebo in adults with raised glucose. Finding prediabetes is the step that makes that possible. For insulin resistance before glucose rises, see our insulin resistance test guide.
Worked example: A1C 5.9% at 48
Illustrative numbers. A 48-year-old man with a BMI of 29 tests at home:
| Marker | Result | Reading |
|---|---|---|
| HbA1c | 5.9% | Prediabetes range |
| Estimated average glucose | 123 mg/dL | 28.7 x 5.9 minus 46.7 (ADAG formula) |
| Triglycerides / HDL | 190 / 38 mg/dL | Ratio 5.0, a pattern that fits insulin resistance |
| ALT | 48 U/L | Mildly raised; fatty liver is one common cause |
| ApoB | 112 mg/dL | Borderline to high (Harvard Health: 90 to 129) |
He takes the results to his doctor, who confirms the A1C on a venous sample or with fasting glucose and discusses a structured lifestyle program. A1C needs about three months to reflect change, so the next home test goes in the calendar for month three, then every three to six months while he works on it. Our blood test for weight loss guide shows which numbers usually move first.
What to do after a prediabetes result
| When | What to test | Why |
|---|---|---|
| Now | Confirm with a second test (venous A1C or fasting glucose) | NIDDK: doctors usually confirm with a second test |
| After about 3 months | HbA1c, triglycerides, ALT | A1C reflects roughly the last three months; triglycerides and ALT often move first |
| Every 3 to 6 months while changing habits | HbA1c, lipids or ApoB | Shows whether the plan is working |
| At least yearly after that | HbA1c or fasting glucose | The ADA's minimum for people with prediabetes |
The Diabetes Prevention Program's lifestyle arm aimed for 7% weight loss and 150 minutes of activity a week, and that is the program behind the 58% risk reduction. Metformin, the other arm, cut it by 31%. Which route suits you is a conversation with your doctor, and a home A1C every three months is a simple way to see whether it is working.
What an at-home test can and cannot do for prediabetes
- Measure HbA1c reliably from a capillary sample, with no fasting
- Add C-peptide, lipids, ApoB and liver markers that show the wider metabolic picture
- Track A1C every 3 months while you change diet and activity
- Diagnose prediabetes or diabetes: a diagnosis needs a clinician and usually a confirming test
- Run an OGTT, or measure fasting glucose on SiPhox EasyDraw panels
- Replace a glucose meter for anyone on insulin
Best-fit SiPhox panel for prediabetes
| If you want | Test | Choose |
|---|---|---|
| Blood sugar plus heart, liver and kidney | HbA1c, C-peptide, TG:HDL, ApoB, Lp(a), ALT, AST, eGFR | Heart & Metabolic |
| Blood sugar plus hormones and vitamin D | HbA1c, eAG, C-peptide, TG:HDL, ApoB, hs-CRP, testosterone or female hormones | Longevity Essentials |
| Blood sugar while on GLP-1 medication | HbA1c plus kidney, liver, iron and B12 | GLP Optimization |
| Fasting insulin, glucose or an OGTT | Venous lab | Your doctor or a lab |
Heart & Metabolic is the natural fit because prediabetes rarely travels alone: liver fat, high triglycerides and raised ApoB come with it. At $124 plus $25, retesting every three months for a year costs $596; twice a year, $298. SiPhox's current EasyDraw panels do not include fasting glucose or fasting insulin.
Heart & Metabolic
Lipids plus kidney and liver function: the panel for cardiovascular and metabolic risk.
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Longevity Essentials
The default panel: heart, metabolic, hormone and inflammation markers in one draw.
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GLP Optimization
Built for people on GLP-1 medication: metabolic, liver, kidney, nutrient and iron markers.
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Frequently asked questions
What A1C level is prediabetes?
5.7% to 6.4%. Under 5.7% is normal and 6.5% or more is in the diabetes range, according to NIDDK and the CDC.
Which is better for prediabetes, A1C or fasting glucose?
Neither is perfect. A1C needs no fasting and averages about three months, but anemia and some hemoglobin variants skew it. Fasting glucose is a one-day snapshot. The OGTT is the most sensitive.
Does prediabetes show on a normal blood test?
Only if the panel includes glucose or HbA1c. A basic metabolic panel includes glucose; HbA1c must usually be ordered separately.
How often should I test if I have prediabetes?
At least once a year, per the American Diabetes Association. While making lifestyle changes, many people recheck A1C every three to six months.
Can prediabetes be reversed?
Often. In the Diabetes Prevention Program, a lifestyle program cut the risk of developing type 2 diabetes by 58% over about three years.
Sources
- NIDDK (NIH): Diabetes tests and diagnosis
- NIDDK (NIH): The A1C test and diabetes
- CDC: National diabetes statistics, data and research (2023 estimates)
- CDC: Prediabetes, your chance to prevent type 2 diabetes
- US Preventive Services Task Force: Screening for prediabetes and type 2 diabetes. JAMA 2021
- Diabetes Prevention Program Research Group: Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002
- American Diabetes Association: Standards of Care in Diabetes 2026, Diabetes Care 49 (Supplement 1)
- Nathan DM et al. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008
- MedlinePlus: Hemoglobin A1C (HbA1c) test
- MedlinePlus: Insulin in blood
- Harvard Health: Is an apoB test a better way to check your cholesterol?
- Diagnostics (Basel) 2025: performance of an upper-arm capillary blood collection device
- SiPhox Health: Heart & Metabolic panel (checked 29 Sep 2026)
- SiPhox Health: Longevity Essentials panel and add-ons (checked 29 Sep 2026)
- SiPhox Health: GLP Optimization panel (checked 29 Sep 2026)