Why Fasting Glucose and HbA1C Are Not The Best Tests

Why Fasting Glucose and HbA1C Are Not The Best Tests

Your annual physical lasts seven minutes. Your doctor glances at your blood work, sees normal fasting glucose and HbA1c, and tells you you're fine.

Meanwhile, you're experiencing brain fog, energy crashes, anxiety, insomnia, and cravings. You answered "yes" to 20+ questions on the blood sugar dysfunction questionnaire. Your symptoms scream blood sugar dysregulation.

But your labs say you're normal.

Here's why standard blood sugar tests miss early dysfunction, and what tests actually catch problems before they become diabetes.

The Problem With Standard Testing

Most physicians rely on two tests to assess blood sugar health:

1. Fasting blood glucose
2. Hemoglobin A1c (HbA1c)

These tests are quick, cheap, and minimally invasive. They're designed for high-volume medical practices where doctors see patients every 5-7 minutes.

This isn't your doctor's fault. Insurance reimbursement doesn't pay for extended visits. Overhead and liability costs force physicians to maximize patient throughput. A 10-minute visit is considered "extended" in today's system.

The tests themselves aren't bad. They're just insufficient for detecting early dysfunction.

Why Fasting Glucose Misses the Problem

Fasting glucose measures how much glucose is circulating in your blood after 8-12 hours without food.

Normal range: 70-99 mg/dL
Pre-diabetes: 100-125 mg/dL
Diabetes: 126+ mg/dL

This tells you one thing: whether your blood sugar is high or low in a fasted state.

What it doesn't tell you:

• How your blood sugar responds to food
• How quickly glucose spikes after eating
• Whether you're experiencing hypoglycemic crashes between meals
• If your pancreas is overproducing insulin to keep fasting glucose artificially normal

You can have perfectly normal fasting glucose and still be in metabolic chaos the rest of the day.

Why HbA1c Has Limitations

HbA1c measures the percentage of hemoglobin (the oxygen-carrying protein in red blood cells) that has glucose attached to it.

Think of hemoglobin like a sponge soaking in syrup. The longer it sits in sugary blood, the more sugar sticks to it.

The theory: Since red blood cells live about 90 days on average, HbA1c reflects your average blood sugar over the past 3 months.

The problem: Red blood cell lifespan varies dramatically based on blood sugar levels.

In people with normal blood sugar: RBCs live 120-150 days
In people with high blood sugar: RBCs live as few as 81 days

This creates a measurement error. If your RBCs die faster (because high blood sugar damages them), your HbA1c appears artificially lower than it should be. You look "better" on paper while your cells are getting hammered.

Conversely, if your RBCs live longer (because your blood sugar is well-controlled), HbA1c can appear slightly elevated even when glucose levels are fine.

HbA1c is useful for monitoring diagnosed diabetics. It's not sensitive enough to catch early dysfunction.

What's Missing: Fasting Insulin

Fasting glucose and HbA1c only measure glucose. They ignore insulin.

Insulin is the hormone that regulates blood sugar. When you eat carbohydrates, your pancreas releases insulin to shuttle glucose into cells.

Early blood sugar dysfunction looks like this:

1. You eat carbs
2. Blood sugar spikes
3. Pancreas releases insulin (often too much)
4. Insulin forces glucose into cells
5. Blood sugar drops (sometimes too low)
6. You feel terrible, crave sugar, eat more carbs
7. Cycle repeats

Your fasting glucose can look perfect because your pancreas is overworking to keep it normal. But you're already insulin resistant—your cells aren't responding to insulin efficiently, so your pancreas has to produce more.

Fasting insulin reveals this.

Optimal fasting insulin: <5 μIU/mL
Functional range: 5-8 μIU/mL
Insulin resistance: >8 μIU/mL

If your fasting insulin is elevated (even with normal glucose), you're already progressing toward diabetes. Standard tests won't catch this for years.

The Better Test: Post-Meal Glucose Monitoring

The best way to assess blood sugar regulation is to measure how your body responds to food in real time.

What you need:

• A standard glucose meter (available at any pharmacy)
• Test strips
• A meal you'd normally eat

The protocol:

1. Measure fasting glucose (before eating)
2. Eat your normal meal
3. Measure glucose 1 hour after eating
4. Measure glucose 2 hours after eating
5. Measure glucose 3 hours after eating

What you're looking for:

Maximum acceptable rise: 40-50 mg/dL in any one-hour period

If your blood sugar spikes above 140 mg/dL at the 1-hour mark, you're pre-diabetic—even if fasting glucose and HbA1c are "normal."

If your blood sugar drops below baseline at the 3-hour mark, you're experiencing reactive hypoglycemia (blood sugar crash after insulin overcompensation).

Real Patient Case Study

A patient came in frustrated. His doctor told him his fasting glucose (82 mg/dL) and HbA1c were "excellent."

But he answered "yes" to 20+ questions on the blood sugar questionnaire. He had afternoon energy crashes, brain fog, irritability before meals, and sugar cravings.

We ran the post-meal glucose test.

Results:

• Fasting: 82 mg/dL (normal)
• 1-hour post-meal: 147 mg/dL (pre-diabetic spike)
• Rise: 65 mg/dL in one hour (too rapid)

His fasting glucose was perfect. His post-meal response was dysfunctional.

Standard testing would have missed this for years—until fasting glucose finally climbed into the pre-diabetic range, by which point significant metabolic damage had already occurred.

After seeing the data, he finally took my advice seriously: cut the bread and simple carbs. His symptoms resolved within weeks.

Comprehensive Blood Sugar Testing

If you want a complete picture of blood sugar health, request these tests:

Fasting tests:

• Fasting glucose (target: 75-85 mg/dL)
• Fasting insulin (target: <5 μIU/mL)
• HbA1c (target: <5.3%)

Calculated ratios:

• HOMA-IR (Homeostatic Model Assessment of Insulin Resistance): Uses fasting glucose and insulin to estimate insulin resistance

Oral glucose tolerance test (OGTT) with insulin:

• Drink 75g glucose solution
• Measure glucose and insulin at 30, 60, 90, 120 minutes
• Reveals how quickly insulin responds and whether it overshoots

Home monitoring:

• Post-meal glucose testing as described above

What to Do If Your Tests Show Dysfunction

If you're showing early signs of blood sugar dysregulation:

Step 1: Eliminate refined carbohydrates and sugar.

This is non-negotiable. Bread, pasta, rice, sugar, fruit juice, and processed foods spike blood sugar. Remove them.

Step 2: Eat protein and fat with every meal.

Protein and fat stabilize blood sugar. They slow glucose absorption and prevent spikes.

For comprehensive nutrition strategies that support blood sugar balance, visit the Fuel Your Body pillar page.

Step 3: Don't skip meals.

Skipping meals causes blood sugar crashes, which trigger cravings and overeating later.

Step 4: Monitor progress with home testing.

Retest post-meal glucose after dietary changes. You should see improvements within 2-4 weeks.

Step 5: Work with a practitioner who understands functional blood sugar management.

Early dysfunction is reversible. But it requires targeted intervention based on your specific patterns—not just generic advice.

The Bottom Line

Standard blood sugar tests catch diabetes after years of damage.

Functional testing catches dysfunction years earlier—when it's still reversible.

If you have symptoms of blood sugar dysregulation (fatigue, brain fog, cravings, mood swings, anxiety), don't accept "your labs are normal" as the final answer.

Test more comprehensively. Your symptoms are real. The standard tests just aren't sensitive enough to detect the problem yet.

Experiencing blood sugar symptoms despite "normal" labs? Dr. JJ Gregor uses comprehensive metabolic testing and Applied Kinesiology to identify early blood sugar dysfunction in his Frisco, Texas practice. Schedule a consultation to catch problems before they become diabetes.