Plasma glucose, commonly known as blood sugar, is a primary energy source for the body's cells and is critical for normal bodily function. It is particularly important for brain function, as the brain primarily uses glucose for energy. Maintaining stable blood glucose levels is vital for overall health, as it ensures a continuous energy supply to the body's tissues and organs. The body tightly regulates these levels through hormones like insulin and glucagon.
Hypoglycemia, or low blood glucose, can occur due to various factors such as excessive insulin production, insufficient dietary intake, or certain medical conditions. Hypoglycemia can lead to symptoms like dizziness, sweating, confusion, shaking, and in severe cases, loss of consciousness or seizures. Chronic low blood glucose can be particularly harmful to the brain and can impair cognitive function and nervous system health.
Hyperglycemia, or high blood glucose, is commonly associated with diabetes when the body either doesn’t produce enough insulin (Type 1 Diabetes) or cannot effectively use the insulin it produces (Type 2 Diabetes). Persistent hyperglycemia can lead to serious complications, including kidney damage, nerve damage, heart disease, and vision problems. It can cause symptoms like frequent urination, increased thirst, fatigue, and blurred vision. The diuretic effect can potentially lead to the loss of electrolytes like sodium and potassium, affecting their balance in the body.
To maintain healthy blood glucose levels:
Adopt a balanced diet that includes complex carbohydrates, fiber, lean proteins, and healthy fats while limiting refined sugars and processed foods.
Engage in regular physical activity, as exercise helps improve insulin sensitivity and glucose uptake by the body's cells.
If you have diabetes, work closely with your healthcare provider to monitor your blood glucose levels and manage your condition through medication, diet, and lifestyle changes.
Be aware of the symptoms of both hypoglycemia and hyperglycemia, and take appropriate action if you experience them, such as adjusting your food intake or seeking medical attention when necessary.
Blood Glucose can be measured in: mg/100mL, mg/dL, mg/L, mg%, mmol/L, µg/mL, µmol/L
Reference ranges represent typical values for healthy individuals. Your healthcare provider must interpret your specific results.
| Age Range | Gender | Unit | Optimal | Normal | Source |
|---|---|---|---|---|---|
| All ages | All genders | mmol/L | - | 3.5 - 5.6 | Güemes, 2016 |
The most basic and commonly measured indicator of blood sugar regulation. It measures the level of glucose in blood after an overnight fast. Persistent high fasting glucose levels are indicative of diabetes or prediabetes.[Mouri, 2023]
Explore 1 additional health topic related to this biomarker in the Health3 app.
Insulin, a hormone secreted by the pancreas, facilitates the uptake of glucose into cells, thereby lowering blood glucose levels. This interaction is critical for maintaining energy homeostasis and disruptions can lead to diabetes mellitus.[Sonksen, 2000][Saltiel, 2001]
HbA1c, or glycated hemoglobin, forms when blood glucose binds to hemoglobin in red blood cells. This process reflects average blood glucose levels over the past two to three months and is used as a biomarker for long-term glucose control in diabetic patients.[Nathan, 2007][Sherwani, 2016]
Explore 4 additional biomarker interactions related to this biomarker in the Health3 app.
A blood glucose test (also called fasting plasma glucose, or FPG when measured after an 8-hour fast) measures the concentration of glucose in your blood at the time of the test. Glucose is the primary fuel for the body's cells — particularly the brain, which relies almost exclusively on glucose for energy. Blood glucose is tightly regulated through the opposing actions of insulin (which lowers glucose by facilitating cellular uptake) and glucagon (which raises glucose by stimulating liver glycogen breakdown).
A fasting blood glucose test is the standard screening test for diabetes and prediabetes recommended by the ADA (American Diabetes Association), WHO, and NICE. It captures your "baseline" glucose when you haven't eaten — removing the variable of recent carbohydrate intake. For a more comprehensive picture of glucose management, clinicians often combine fasting glucose with HbA1c (a 2–3 month average) and sometimes an oral glucose tolerance test (OGTT). For HbA1c and glucose conversion, use the HbA1c to glucose converter. For HOMA-IR insulin resistance calculation, see the HOMA-IR calculator.
Note: US labs typically report in mg/dL; most other countries use mmol/L. Use the blood test unit converter to switch between units. A single fasting glucose ≥126 mg/dL should be confirmed on a repeat test before a diagnosis of diabetes is made (unless accompanied by unequivocal hyperglycaemia symptoms).
Fasting hyperglycaemia most commonly reflects impaired insulin function (either insufficient insulin production or insulin resistance). Key presentations:
Symptoms of hyperglycaemia include frequent urination, increased thirst, blurred vision, fatigue, and slow wound healing. See the broader context in blood sugar markers explained and the Metabolic Health topic page.
Hypoglycaemia (fasting glucose <70 mg/dL or <3.9 mmol/L) is less common but can be dangerous. Causes include:
Symptoms of hypoglycaemia include shakiness, sweating, palpitations, confusion, and in severe cases, loss of consciousness or seizures.
Fasting glucose gives a snapshot; trends over months tell a more useful story. Combined with HbA1c (which reflects average blood glucose over 2–3 months), regular fasting glucose monitoring can reveal whether lifestyle interventions or medications are working. The ADA recommends HbA1c testing at least twice yearly for people with stable, well-controlled diabetes, and quarterly when not at goal.
For people with prediabetes, monitoring fasting glucose annually (or every 6 months if previously borderline) gives valuable early warning of progression. Health3 lets you track fasting glucose and view trends alongside HbA1c and other metabolic markers.
For a full metabolic health picture, also consider fasting insulin alongside fasting glucose to calculate HOMA-IR (insulin resistance index). Use the HOMA-IR calculator. See also the blood test tracking use case pages for athletes monitoring metabolic health.
The ADA defines normal fasting glucose as below 100 mg/dL (<5.6 mmol/L). Some functional medicine practitioners prefer to see levels below 90 mg/dL (<5.0 mmol/L) as optimal, though the evidence base for this more stringent target is less established than the ADA threshold.
Fasting glucose is measured after at least 8 hours without food and is the standard test for diabetes screening. Random glucose is taken at any time regardless of last meal. A random glucose ≥200 mg/dL (≥11.1 mmol/L) with classic symptoms (thirst, frequent urination) is sufficient to diagnose diabetes without fasting confirmation. For screening purposes, fasting glucose is preferred as it removes dietary variability.
Per ADA/WHO criteria, a fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or above, confirmed on two separate occasions, indicates diabetes. A single result in a symptomatic patient may be sufficient for diagnosis. Prediabetes is 100–125 mg/dL (ADA) or 110–125 mg/dL (WHO).
Yes — the Diabetes Prevention Program (DPP) RCT showed that intensive lifestyle changes (5–7% weight loss + 150 min/week moderate activity) reduced progression from prediabetes to type 2 diabetes by 58% over 3 years — more effective than metformin (31%). Many people with prediabetes who make sustained dietary and exercise changes return their fasting glucose to normal range.
Fasting blood glucose is a snapshot of your glucose level right now (or this morning). HbA1c reflects the percentage of haemoglobin glycated over the past 2–3 months, giving a longer-term average. HbA1c of 6.5% or above indicates diabetes; 5.7–6.4% indicates prediabetes (ADA). Both tests are complementary — fasting glucose can detect acute changes faster, while HbA1c is a better indicator of sustained control. Use our HbA1c to glucose converter to see how they relate.
This is known as the "dawn phenomenon" — early morning cortisol and growth hormone spikes raise blood glucose as the body prepares for waking. It is more pronounced in people with diabetes or insulin resistance. Stress can also elevate morning glucose. If your fasting glucose is consistently high in the morning despite dietary control, discuss this pattern with your healthcare provider — it may indicate a need for medication adjustment or further investigation.
This page is for educational purposes only. A single elevated blood glucose result does not diagnose diabetes — confirmation requires repeat testing and clinical evaluation. Blood glucose thresholds vary by test type (fasting, random, OGTT) and laboratory. Always discuss glucose results with a qualified healthcare provider. Health3 is a tracking and awareness tool, not a diagnostic service.
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