A borderline result sits in a zone a guideline has named, like prediabetes or borderline-high LDL, or just past a healthy limit your lab doesn't print. It is rarely urgent. It is a reason to retest and check what else moved.
Most borderline results are not an emergency. Three things decide whether one matters: whether a guideline names the zone you're in, whether the number is moving between tests, and whether other markers point the same way. A fasting glucose of 105 mg/dL is ADA prediabetes and worth acting on. A TSH of 2.8 mIU/L is not borderline under any guideline, even though some sources would prefer it lower.
Guideline bands below are the ones FixFirst's analysis uses. Longevity targets belong to the people named beside them. They are not FixFirst's clinical claims, and this page has not been medically reviewed.
The in-range and borderline columns come from clinical guidelines. The last column is what longevity physicians and researchers cite for themselves and their patients: stricter, and attributed to each person.
| Marker | In range (guideline) | Borderline zone | Longevity target (who cites it) |
|---|---|---|---|
| Fasting glucose | 70–99 mg/dLADA | 100–125 mg/dL: prediabetesADA · UK: NICE uses 5.5–6.9 mmol/L | 70–85 mg/dLAttia, Means, LustigFunctional "optimal": 75–86 → |
| HbA1c | Under 5.7%ADA | 5.7–6.4%: prediabetesADA · UK: NICE uses 42–47 mmol/mol (6.0–6.4%) | Under 5.5%Attia · under 5.4%: Ferriss · 5–5.4%: Means |
| LDL cholesterol | Under 100 mg/dLATP III "optimal" | 100–129 "above optimal"; 130–159 "borderline high"ATP III | No LDL target citedAttia, Huberman and Means track ApoB instead |
| Triglycerides | Under 150 mg/dLATP III | 150–199 mg/dL: borderline highATP III | Under 100 mg/dLAttia |
| ApoB | Under 90 mg/dL, general preventionACC/AHA | No named borderline zoneTargets drop to under 70 or 55 mg/dL at higher risk | Under 65 mg/dLAttia · under 60: Huberman · under 80: Means |
| hs-CRP | Under 1.0 mg/L: low riskACC/AHA | 1.0–3.0 mg/L: intermediate riskACC/AHA | Under 1.0 mg/LAttia, Ferriss |
| TSH | 0.4–4.0 mIU/LATA | Above the upper limit with normal free T4: subclinical hypothyroidismATA | 1–2 mIU/LOptimalDX, a functional-medicine source; no longevity physician in our sources cites oneHow much weight that 1–2 carries → |
| ALT | Up to about 25 U/L (women), 33 U/L (men)ACG 2017 healthy limits; many labs print 40 or higher | Under 2× the upper limit: "borderline" elevationACG 2017 | Under 20 U/L, ALT and ASTAttia |
| Ferritin | 30 ng/mL or aboveNICE | Under 30 ng/mL: consistent with iron deficiency, even when the lab range starts lowerNICE | 50–100 ng/mLPatrick · 30–60: Johnson, deliberately lowerFunctional "optimal": above 100 → |
| Vitamin D | 30 ng/mL or aboveEndocrine Society, 2011 | 20–29 ng/mL: insufficientEndocrine Society, 2011. The IOM treats 20 as enough for bone health | 40–60 ng/mLPatrick, Johnson · above 40: HubermanFunctional "optimal": 50–90 → |
| Homocysteine | Up to 10 µmol/LNIH-referenced risk tiers | 10–15 µmol/L: borderlineAbove 15 is treated as elevated | Under 10 µmol/LAttia · under 8: Sinclair |
| Uric acid | Up to 6.8 mg/dL, where urate starts to crystalliseACR | Above 6.8 with no gout: asymptomatic hyperuricaemiaACR 2020 advises against drug treatment for it | Under 5.0 mg/dLAttia · under 5.5: Lustig |
Units are US (mg/dL) unless noted. UK glucose and HbA1c cut-offs differ from the ADA's, so both are shown. For the difference between a lab's "normal" range and the "optimal" ranges functional-medicine sources propose, see optimal vs normal blood test ranges. Named longevity panels are covered in longevity blood markers. If your results are all in range but you still feel unwell, labs normal, still tired? covers the six markers most often behind it.
It is normal. 2.8 mIU/L sits inside the 0.4–4.0 range the ATA uses and is not borderline under any guideline. Some functional-medicine sources prefer 1–2, but none of the major guidelines treats 2.8 as a problem on its own. If you have symptoms, ask whether free T4 and thyroid antibodies (TPO) were tested, and compare with earlier results. A rising trend tells you more than one value. More on the thresholds in high TSH.
Under ADA criteria it is prediabetes: 100–125 mg/dL is impaired fasting glucose. In UK units 105 mg/dL is 5.8 mmol/L, which NICE's 5.5–6.9 range also counts as high risk. One reading is not a diagnosis, and the ADA asks for a repeat test, often an HbA1c. This is the most actionable borderline zone on the list. In the Diabetes Prevention Program, lifestyle change cut progression to type 2 diabetes by 58%. If your triglycerides are also high, read high glucose and high triglycerides.
Usually not urgently. The American College of Gastroenterology calls an elevation under twice the upper limit "borderline". Common causes are fatty liver, alcohol, some medicines, and hard exercise in the days before the test, which raises AST from muscle. The usual next step is a repeat test and a look at the pattern with your doctor. The ACG's healthy ALT limits (about 25 U/L for women, 33 for men) are lower than many labs print, so a value your report calls normal can still sit above them.
Borderline results are common on any panel. These decide which ones deserve attention.
Named zones (prediabetes, borderline-high LDL, intermediate-risk hs-CRP) come with outcome evidence and specific advice. A value just past a lab's printed limit, with no named zone, carries less weight.
Compare with your last report. A result that has crept up across two or three tests matters more than where one result lands.
Borderline glucose, triglycerides and ALT together point toward insulin resistance. Any one of them alone may not. Several results out of range covers how to read them together.
A non-fasting sample raises glucose and triglycerides. A recent infection raises hs-CRP and ferritin. Hard training raises AST. Biotin supplements can distort some thyroid assays.
FixFirst reads every marker on your report against guideline bands like the ones above, using sex- and age-adjusted thresholds where the guideline sets them. It then ranks the results, so a report with five flags shows which one to look at first. It does not score you against the longevity targets.
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