Statistical Average vs. Optimal: A Functional Lab Range Guide

Two different definitions of "normal"

When you look at a lab report, every value has a reference range next to it. That range is built from a statistical average of the lab's patient population — not from people who are thriving.

Functional medicine uses a different yardstick: optimal ranges, derived from research on people who feel and perform well, with low inflammation and stable metabolic markers.

Below is a practical, lab-by-lab comparison you can bring to your next appointment.

Thyroid panel

Marker	Conventional "normal"	Functional optimal
TSH	0.45 – 4.5 mIU/L	1.0 – 2.0 mIU/L
Free T4	0.8 – 1.8 ng/dL	1.1 – 1.5 ng/dL
Free T3	2.3 – 4.2 pg/mL	3.2 – 4.0 pg/mL
Reverse T3	9 – 24 ng/dL	< 15 ng/dL
TPO antibodies	< 35 IU/mL	Ideally undetectable

Iron status

Marker	Conventional	Functional
Ferritin (women)	15 – 200 ng/mL	70 – 100 ng/mL
Ferritin (men)	30 – 400 ng/mL	100 – 150 ng/mL
Serum iron	50 – 170 µg/dL	85 – 130 µg/dL
TIBC	250 – 450 µg/dL	250 – 310 µg/dL
% saturation	15 – 50%	25 – 35%

Low ferritin is one of the most common — and most missed — drivers of fatigue, hair loss, and poor thyroid conversion in women.

Blood sugar & insulin

Marker	Conventional	Functional
Fasting glucose	70 – 99 mg/dL	75 – 86 mg/dL
Hemoglobin A1c	< 5.7%	< 5.3%
Fasting insulin	< 25 µIU/mL	2 – 5 µIU/mL
HOMA-IR	< 2.5	< 1.0

A fasting glucose of 96 is "normal" but functionally pre-diabetic. A fasting insulin of 18 is "normal" but indicates years of metabolic dysfunction.

Inflammation

Marker	Conventional	Functional
hs-CRP	< 3.0 mg/L	< 0.5 mg/L
Homocysteine	< 15 µmol/L	< 7 µmol/L
Fibrinogen	200 – 400 mg/dL	200 – 300 mg/dL

Elevated hs-CRP and homocysteine show up years before cardiovascular disease, autoimmunity, and cognitive decline.

Vitamin & mineral status

Marker	Conventional	Functional
Vitamin D (25-OH)	> 30 ng/mL	50 – 80 ng/mL
Vitamin B12	> 200 pg/mL	600 – 900 pg/mL
Magnesium RBC	4.2 – 6.8 mg/dL	6.0 – 6.5 mg/dL
Folate	> 3 ng/mL	> 15 ng/mL

B12 deficiency symptoms — neuropathy, brain fog, fatigue, mood changes — start well above the "deficient" cutoff. Japan uses 500 as the lower limit. The US still uses 200.

Lipids — the often-mis-told story

Marker	Conventional	Functional
Total cholesterol	< 200 mg/dL	160 – 200 mg/dL
LDL	< 100 mg/dL	< 100, but particle size matters more
HDL	> 40 (M) / > 50 (W)	> 55
Triglycerides	< 150 mg/dL	< 80 mg/dL
Trig:HDL ratio	not reported	< 1.5

Triglyceride-to-HDL ratio is one of the most predictive cardiovascular markers — and most labs don't even calculate it for you.

How to use this guide

1. Pull your last three years of labs. Look at trends, not single data points.
2. Highlight anything that is "normal" but outside the functional range. That is your gray zone.
3. Stack the gray-zone findings against your symptoms. Patterns will emerge — usually thyroid + iron + blood sugar, or inflammation + B vitamins + D.
4. Get a functional interpretation. Either a practitioner or a tool that reads through the optimal lens.

The goal is not to panic over every yellow flag. The goal is to catch the drift early — when it is still a lifestyle conversation and not a prescription.

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🎙️ Listen to the Episode

This article pairs with our podcast episode "Normal Labs, Sh*t Life: Why Your Bloodwork Is Lying to You." Dr. Nicole unpacks the reference-range trap, the labs your doctor almost certainly skipped, and how to read your own results through a functional lens.

▶ Listen to the full episode →