"Normal" on your lab report means you fall inside a wide statistical band, not that your result is ideal. Here's what "optimal" ranges actually claim, who proposes them, and which claims hold up.
A "normal" reference range is statistical — labs set it so roughly 95% of a broad, unselected population falls inside it, whether or not those people are actually healthy. An "optimal" range is a narrower band proposed mostly by functional-medicine sources, meant to reflect fewer symptoms or better long-term markers. Optimal ranges aren't standardised: they vary from source to source, and only some are backed by mainstream clinical evidence.
The specific "optimal" figures below are attributed to their original sources so you can see exactly whose opinion they represent — they are not FixFirst's clinical claims.
Reference ranges are built from a population, not from an outcome.
When a lab sets a reference range, it typically draws blood from a large sample of people, throws out the top and bottom 2.5%, and calls the remaining 95% "normal." That sample usually isn't screened for how healthy those people actually are — it includes people who are sedentary, under-slept, or metabolically stressed alongside people in excellent health. The range describes what's common, not what's ideal.
That's why two people can both get a "normal" result on the same test with very different implications. A ferritin of 15 ng/mL and a ferritin of 150 ng/mL might both sit inside one lab's stated reference range, but the person at 15 is far closer to iron-deficiency symptoms than the person at 150. The label "normal" hides that gap.
It also explains why the disagreement persists: conventional medicine's reference range is built to answer one question — is this result outside the range associated with a diagnosable disease? Functional-medicine and longevity practitioners are asking a different question — is this result in the part of the range associated with feeling and functioning well? Both questions are legitimate. They just aren't the same question, and a single number can answer one while leaving the other open.
Functional-medicine practitioners and platforms propose narrower target ranges. These numbers are specific to the sources cited — not a FixFirst recommendation.
| Biomarker | Standard reference range | "Optimal" range proposed | Source |
|---|---|---|---|
| Fasting glucose | 70–99 mg/dL | 75–86 mg/dL | OptimalDX |
| TSH | 0.45–4.5 mIU/L | 1–2 mIU/L | OptimalDX |
| Vitamin D | 30–100 ng/mL | 50–90 ng/mL | OptimalDX |
| Magnesium | 1.5–2.6 mg/dL | >2.0 mg/dL | OptimalDX |
| Ferritin | Varies by lab and sex | >100 ng/mL | OptimalDX |
| hs-CRP | <3.0 mg/L (low risk) | <1.0 mg/L | KC Primary Care biomarker table |
| ApoB | No single agreed cutoff; many labs flag <90 mg/dL as "desirable" | <90 mg/dL (general) · <70 mg/dL (high risk) · <55 mg/dL (very high risk, prior cardiovascular event) | 2026 ACC/AHA Dyslipidemia Guideline |
Notice that none of these "optimal" figures come with a citation to a clinical trial showing better outcomes at the narrower band. That's the honest caveat: some track mainstream guidance reasonably well (a TSH near 1–2 is a target many endocrinologists would agree is preferable to sitting at 4.5), while others are narrower than anything a published guideline supports, and vary from one functional-medicine source to the next.
ApoB is the one row in this table that isn't a functional-medicine opinion at all — it's mainstream cardiology, and it just moved. The 2026 ACC/AHA multisociety dyslipidemia guideline introduced risk-tiered ApoB targets for the first time, tightening to below 55 mg/dL for patients with a prior cardiovascular event. It's a useful case study for the whole "normal vs. optimal" debate: the target isn't fixed, it depends on your individual risk category, and unlike most of the functional-medicine figures above, it's backed by a named clinical guideline rather than a practitioner's practice pattern.
Named longevity physicians and researchers publish their own versions of this same table, ApoB included. The Longevity blood markers section covers what Peter Attia, Andrew Huberman, and others have cited publicly, each target attributed to the person and the source rather than treated as a FixFirst claim.
Not every "optimal" claim carries the same weight. Here's how to tell the difference.
A TSH in the 1–2 mIU/L range being preferable to one near the top of the reference range (4.5) reflects fairly broad endocrine opinion, even though it isn't a universal diagnostic cutoff. ApoB's risk-tiered targets go further — they're written into the 2026 ACC/AHA guideline itself, not just informal opinion.
Ferritin above 100 ng/mL as a symptom-free target is a reasonable clinical observation in iron-deficiency research, but there's no single agreed number, and it can shift with inflammation.
Narrow bands for glucose or magnesium that tighten a wide clinical range by 60–80% aren't supported by outcome studies — they're a functional-medicine practice pattern, not a guideline.
The risk in treating every "optimal" number as a target is that chasing it can lead to unsupervised supplementation aimed at a band that was never clinically validated — for example, iron or vitamin D supplementation pushed toward the top of an "optimal" range without a documented deficiency, which carries its own downside. Use these ranges as a prompt for a conversation with your doctor, not a self-treatment target.
FixFirst doesn't invent its own "optimal" band for your results — we won't hand you a number nobody can defend. What it does instead is rank every marker on your report by clinical priority, using established sex- and age-adjusted thresholds, so you can see which "normal" results are borderline and worth watching, and which abnormal ones actually matter most right now. That's a narrower, more defensible promise than "optimal" — but it's the part of this problem that's actually solvable today.
Upload your report and get a ranked, evidence-based read on every marker — including the borderline values inside the reference range that most labs don't flag. 45 seconds, free, no account.
Analyse My Report Free