Glucose (Blood Sugar)

What is Glucose?

Glucose is a simple sugar that serves as the primary energy source for your cells. When you eat carbohydrates, your body breaks them down into glucose, which enters your bloodstream.

Fasting glucose tests measure blood sugar after 8–12 hours without food, giving a baseline reading of how well your body regulates sugar.

Your pancreas produces insulin to help cells absorb glucose. When this system doesn't work properly, blood sugar levels rise — the hallmark of diabetes.

Normal Ranges (Fasting)

Category	Fasting Glucose
Normal	Below 100 mg/dL (5.6 mmol/L)
Prediabetes	100–125 mg/dL (5.6–6.9 mmol/L)
Diabetes	126 mg/dL or higher (7.0+ mmol/L)

A diabetes diagnosis requires confirmation with a second test on a different day.

Why It Matters

Diabetes Prevention

Catching elevated glucose in the prediabetes range gives you the opportunity to make lifestyle changes before developing type 2 diabetes.

Energy and Mood

Blood sugar fluctuations affect energy levels, concentration, and mood. Understanding your glucose patterns can explain symptoms like afternoon fatigue or irritability.

Long-Term Health

Chronically elevated glucose damages blood vessels and nerves over time, increasing risk of heart disease, kidney disease, vision problems, and neuropathy.

Factors That Affect Glucose

Recent meals — That's why fasting tests are standard
Stress — Cortisol raises blood sugar
Sleep quality — Poor sleep impairs glucose regulation
Physical activity — Exercise lowers blood sugar
Medications — Steroids, some blood pressure drugs can raise glucose

Glucose vs. HbA1c

Fasting glucose shows your blood sugar at one moment. HbA1c shows your average over 2–3 months. Both are useful:

Glucose: Good for detecting acute changes
HbA1c: Better for assessing long-term control

How Often to Test

No risk factors: Every 3 years after age 45
Overweight or family history: Every 1–3 years
Prediabetes: Annually
Diabetes: As directed (often daily self-monitoring)