Have you ever been told your blood tests are “normal”—but deep down, you know something isn’t right?
Many people experience symptoms like fatigue, brain fog, cravings, or stubborn weight gain long before traditional lab tests flag a problem. That’s because standard lab reference ranges are designed to detect disease—not to optimise health or catch early dysfunction.
In functional medicine, we look at blood sugar markers through a more preventative and personalised lens. Here’s how to understand your glucose, insulin, and HbA1c levels—and what they might be trying to tell you.
1. Fasting Glucose – The Starting Point
What it measures:
Your blood sugar level after 8–12 hours of fasting.
Conventional Range: 70–99 mg/dL (3.9–5.5 mmol/L)
Optimal Functional Range: 82–88 mg/dL (4.5–4.9 mmol/L)
Why it matters:
Levels above 90–92 mg/dL (5.0–5.1 mmol/L) may indicate early blood sugar dysregulation—even if your doctor says it’s “normal.” Functional medicine aims to catch these early shifts before they progress to insulin resistance or type 2 diabetes.
2. Fasting Insulin – A Powerful Early Indicator
What it measures:
How much insulin your pancreas is releasing to keep your blood sugar stable.
Conventional Range: <25 µIU/mL
Optimal Functional Range: 2–6 µIU/mL
Why it matters:
You can have “normal” blood sugar and still have high insulin—meaning your body is working overtime to maintain balance. Chronically high insulin is a red flag for insulin resistance, weight gain, PCOS, and inflammation.
HOMA-IR – Calculating Your Insulin Resistance Score
What it measures:
HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) estimates how resistant your cells are to insulin by using your fasting glucose and fasting insulin values.
Formula:
(Fasting Glucose in mmol/L × Fasting Insulin in µIU/mL) ÷ 22.5
Example:
Fasting glucose: 5.1 mmol/L
Fasting insulin: 8 µIU/mL(5.1 × 8) ÷ 22.5 = 1.81
Functional Range Interpretation:
<1.0: Optimal insulin sensitivity
1.0–1.9: Mild insulin resistance
2.0–2.9: Moderate insulin resistance
≥3.0: Significant insulin resistance
Why it matters:
HOMA-IR can reveal early insulin resistance even when individual glucose and insulin results still appear “normal.” It’s a powerful early detection tool that gives a clearer picture of your metabolic state.
Note: Most labs don’t calculate this automatically, but it’s simple to do with your own test results—or with guidance from a functional medicine practitioner.
3. HbA1c – Your 3-Month Average
What it measures:
The percentage of sugar bound to red blood cells over the past 2–3 months.
Conventional Range: <5.7%
Optimal Functional Range: 5.0–5.3%
Why it matters:
HbA1c can miss glucose spikes and crashes, especially in people with fluctuating blood sugar. It’s a helpful marker, but it shouldn’t be used in isolation.
A “normal” HbA1c with high insulin may still indicate early metabolic dysfunction.
4. C-Peptide – Understanding Insulin Production
What it measures:
How much insulin your body is producing (as a byproduct of insulin secretion).
Why it matters:
Low C-peptide = low insulin production (potential beta-cell fatigue)
High C-peptide = overproduction (often due to insulin resistance)
This is a useful test in both early-stage and long-standing blood sugar issues.
5. Glucose Tolerance and Post-Meal Testing
A functional approach also includes looking at how your blood sugar behaves after meals:
1-hour post-meal glucose should ideally stay below 140 mg/dL (7.8 mmol/L)
2-hour post-meal glucose should return to below 120 mg/dL (6.7 mmol/L)
Continuous Glucose Monitors (CGMs) can offer real-time insights into how meals, stress, and sleep impact your glucose levels.
Functional vs Conventional: Why the Ranges Matter
Standard reference ranges are based on the average population—not the healthiest population. Functional ranges are tighter and based on optimal physiology, which means they can detect dysfunction before disease develops.
By identifying imbalances early, you can take action before blood sugar problems become chronic.
When to Test Your Blood Sugar Markers
Annually as a check-in
If you experience symptoms like cravings, fatigue, irritability, or poor sleep
If you have a family history of diabetes or metabolic syndrome
If you’re dealing with PCOS, thyroid issues, or autoimmune conditions
Final Thoughts
Your lab results are more than just numbers—they’re clues to your metabolic story. Understanding them from a functional perspective gives you the power to take control of your energy, weight, mood, and long-term health.
Ready to uncover the full picture of your metabolic health? Book a consultation or download my 7-Day Blood Sugar Reset to start restoring balance now.