Glucose in Plasma (Fasting)
This test measures your blood sugar level after you’ve gone without food for at least 8 hours. It helps assess your body’s ability to process glucose and can help detect diabetes or other metabolic conditions.
["A fasting plasma glucose test checks for high blood sugar that may signal diabetes or prediabetes."]
Key facts at a glance
- LOINC
- 18296-4
- Short code
- Glucose p Glc SerPl-Imp
- Synonyms
- Glucose p Glc SerPl-Imp
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 70
- Ref high
- 100
- Critical range
- 50 N/A – 400 N/A
- Fasting
- true
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82947
- SNOMED
- 260395008
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters
Fasting plasma glucose is a critical part of diagnosing type 2 diabetes and prediabetes. Your doctor may order this test if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, or if you have risk factors like obesity, a family history of diabetes, or high blood pressure.
How the Test Works
You’ll fast (not eat or drink anything except water) for at least 8 hours before the test. A healthcare provider will draw blood from a vein in your arm. The blood sample is sent to a lab where glucose levels are measured using an enzymatic method.
What to Expect Before the Test
Plan ahead: Wear comfortable clothing, bring any medications you take daily, and arrange for someone to drive you home if you feel dizzy or lightheaded after the blood draw. Avoid caffeine or sugary drinks before the test.
What to Expect During the Test
The blood draw usually takes a few minutes. You may feel a slight pinch, but most people tolerate it well. The site may sting briefly, but this is normal. You can resume normal activities immediately after.
Reference range
Fasting: 70-100 mg/dLN/A
Fasting for 8-12 hours required. Water is permitted. Avoid chewing gum and smoking before the test.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test helps identify high blood sugar levels that may indicate diabetes or insulin resistance. Elevated results can signal an increased risk of long-term complications like nerve damage, kidney disease, or heart disease. Low results may prompt further evaluation for conditions like hypoglycemia or hormonal imbalances.
Short name
Fasting Plasma Glucose
Frequently asked questions
Why did my doctor order this test?
What do my results mean?
Can I eat or drink anything before the test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy