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Fasting Blood Glucose (FBG) Test

✅ Up to date🔬 Evidence: StrongEndocrine & Metabolism
Diğer adları: Blood sugar test, Fasting blood sugar, Fasting glucose
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Discuss your test results with your doctor. This page is for informational purposes only and does not provide a diagnosis.

⚡ Key Facts

• Measures blood glucose after at least 8 hours of fasting • Normal: 70–99 mg/dL (3.9–5.5 mmol/L) • 100–125 mg/dL is considered prediabetes • ≥126 mg/dL on two separate occasions suggests diabetes • One of the key tests in diabetes and prediabetes assessment

🧪 What Does This Test Measure?

The fasting blood glucose test measures the level of glucose in the blood after at least 8 hours of fasting, reflecting how well the body regulates blood sugar at rest.

📋 Why Is It Ordered?

Ordered for diabetes and prediabetes assessment, monitoring of existing diabetes, and investigation of hypoglycemia. The ADA recommends screening in certain adults over 35.

🔧 Preparation

At least 8 hours of fasting (ideally 8–12 hours) is required. Only water is permitted during this period. The test is typically performed in the early morning.

📊 Reference Ranges

Normal: 70–99 mg/dL (3.9–5.5 mmol/L) Prediabetes: 100–125 mg/dL (5.6–6.9 mmol/L) Diabetes: ≥126 mg/dL (≥7.0 mmol/L) Hypoglycemia: <70 mg/dL (<3.9 mmol/L) ⚠️ These thresholds may vary by guideline and laboratory. Discuss your results with your doctor.

⬆️ High Values

Elevated fasting glucose may be associated with diabetes, prediabetes, or insulin resistance. Stress, poor sleep, and certain medications can also temporarily raise results.

⬇️ Low Values

Low fasting glucose (<70 mg/dL) is considered hypoglycemia. It may be associated with diabetes medication overdose, prolonged fasting, alcohol use, or rare endocrine disorders.

⚙️ What Can Affect Results?

Certain conditions may make fasting glucose less reliable: fasting duration, stress, sleep quality, medications, physical activity, and time of testing.

🔬 Evidence Summary

Strong evidence: 3 guidelines, 1 systematic review, and supporting observational studies.

✅ Key Takeaways

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What you learned: Fasting blood glucose between 70–99 mg/dL is considered normal. Results of 100 mg/dL or above may warrant further evaluation with your doctor.

⛔

A single fasting glucose result cannot diagnose diabetes on its own. Clinical context and confirmatory testing are needed.

🔬 Sources Used on This Page

10 sources · Most recent publication: 2025
📋
Guideline
Expert society and guideline recommendations
3
sources
📊
Systematic review / meta-analysis
Combined analysis of multiple studies
1
source
📖
Review
Comprehensive topic evaluation
1
source
👁
Observational
Observational and cohort studies
5
sources
Overall assessment: Evidence level for this topic is strong. This page is supported by 3 guidelines, 1 systematic review/meta-analysis, 1 review, 5 observational studies.

📝 Questions to Ask Your Doctor

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Last reviewed: 3/25/2026
Next review: 6/25/2026

🔗 Related Topics

🩺 Type 2 diabetes🩺 Prediabetes🧪 HbA1c (Glycated hemoglobin)🧪 OGTT (Oral glucose tolerance test)🧪 Fasting insulin🧪 HOMA-IR
⚖️ This page does not replace medical advice. Make treatment decisions with your doctor.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.