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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
⚠️
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.
📚 Most Important Studies on This Topic
✅ Key Takeaways
💡
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
9 sources · Most recent publication: 2026📋
Guideline
Expert society and guideline recommendations
2
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 2 guidelines, 1 systematic review/meta-analysis, 1 review, 5 observational studies.
📝 Questions to Ask Your Doctor
Be prepared for your appointment. Add questions to your list.
📋 References
[PMID: 41358893] Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2026. Diabetes Care, 2026.
[PMID: 36258973] Stress-Induced Diabetes: A Review. Cureus, 2022.
[PMID: 27493821] Generalized Anxiety Disorder and Hypoglycemia Symptoms Improved with Diet Modification. Case Reports in Psychiatry, 2016.
[PMID: 24895042] Clinical implication of fasting and post-challenged plasma glucose in diagnosis of diabetes mellitus. Endocrine, 2015.
[PMID: 19450031] Daily Negative Mood Affects Fasting Glucose in Type 2 Diabetes. Health Psychology, 2009.
[PMID: 12547851] Diagnostic strategies to detect glucose intolerance in a multiethnic population. Diabetes Care, 2003.
[PMID: 10382583] Is fasting glucose sufficient to define diabetes? Epidemiological data from 20 European studies. Diabetologia, 1999.
[PMID: 9686693] Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus. WHO, 1999.
[PMID: 10372239] How valid is fasting plasma glucose as a parameter of glycemic control in non-insulin-using patients with type 2 diabetes?. Diabetes Care, 1999.
Last reviewed: 3/25/2026
Next review: 3/25/2027
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⚖️ 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.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.