AI Summary The fasting glucose test measures blood sugar after at least 8 hours without food or drink except water. Doctors use it to screen for diabetes and prediabetes and to assess MASLD and MASH risk, since insulin resistance links blood sugar and liver fat. A normal result is 70–99 mg/dL; 126 mg/dL or higher on two occasions supports diabetes. Your doctor confirms results and may order follow-up tests. Results usually arrive within a day or two.
Source: www.liverdirectory.com
Medically Reviewed.
Fasting glucose is a simple blood test that measures how much sugar is in your blood after not eating or drinking anything but water for at least 8 hours. It is one of the standard tests doctors use to check for diabetes and prediabetes, and it is also part of the metabolic workup used to assess risk for MASLD (metabolic dysfunction-associated steatotic liver disease) and MASH.
Blood sugar and liver health are closely connected. Insulin resistance — when your body's cells don't respond normally to insulin — is a key driver of fat buildup in the liver, and elevated fasting glucose is often one of the earliest signs of it.
Liver Health AI Assistant
Ask Aimy
Aimy answers from LiverDirectory’s reviewed health information — helping patients make sense of liver-health terms, prepare for specialist visits, and explore what to look up next.
ABOUT THIS TEST
Fasting glucose (also called fasting blood sugar) measures the amount of glucose circulating in your blood after you have not eaten or drunk anything but water for at least 8 hours, usually overnight. It is one of the most common blood tests used to check for diabetes and prediabetes.
WHY DOCTORS ORDER THIS TEST
Fasting glucose is one of the standard blood tests used to diagnose type 2 diabetes. A doctor may order it as part of routine bloodwork, or because of symptoms like excess thirst, frequent urination, or unexplained fatigue.
Impaired fasting glucose or diagnosed diabetes counts as a cardiometabolic risk factor. Having hepatic steatosis (fat in the liver) plus at least one cardiometabolic risk factor — including abnormal fasting glucose — supports a diagnosis of MASLD.
If you already have MASLD, MASH, or diabetes, your doctor may recheck fasting glucose periodically to see whether your blood sugar control is improving, stable, or getting worse over time.
When liver blood tests such as ALT or AST come back abnormal, checking fasting glucose alongside other metabolic markers helps a doctor understand whether insulin resistance or diabetes could be contributing to liver stress.
BLOOD SUGAR REFERENCE RANGES
Fasting glucose is measured in milligrams per deciliter (mg/dL). These are the standard interpretive ranges used by U.S. clinicians.
The amount of sugar circulating in your blood after fasting for at least 8 hours; reflects how well your body regulates blood sugar between meals.
70–99 mg/dL
Below 70 mg/dL may indicate hypoglycemia (low blood sugar), which can occur with certain medications, prolonged fasting, or other medical conditions.
70–99 mg/dL is the expected range for someone without diabetes.
100 mg/dL or higher may indicate prediabetes (100–125 mg/dL) or diabetes (126 mg/dL or higher, confirmed on two separate occasions). Higher fasting glucose is also linked to greater insulin resistance and MASLD risk.
Diabetes is diagnosed when fasting glucose is 126 mg/dL or higher on two different occasions, or confirmed with an A1C of 6.5% or higher or an oral glucose tolerance test result of 200 mg/dL or higher.
AFTER TESTING
A single high fasting glucose reading does not confirm diabetes on its own. Your doctor will usually repeat the test on a separate day, or confirm with an HbA1c or oral glucose tolerance test, before making a diagnosis.
If your fasting glucose is elevated and you also have hepatic steatosis (fat detected in the liver on imaging), your doctor may evaluate you for MASLD or MASH, since abnormal fasting glucose counts as a cardiometabolic risk factor.
Depending on your results, your doctor may recommend lifestyle changes, refer you to a specialist for diabetes or liver care, or order follow-up tests such as HbA1c, insulin, or a lipid panel to build a fuller metabolic picture.
TEST DAY EXPECTATIONS
Ask your doctor exactly how long to fast — typically at least 8 hours, often overnight. You may drink water during this time, but avoid food, sugary drinks, coffee, and, if possible, smoking.
A clinician will draw a small blood sample from a vein, usually in your arm. The process takes only a few minutes. Some people feel mild pinching or brief lightheadedness, especially when fasting.
You can eat and drink normally right after your blood is drawn. Results are typically available within a day or two through your doctor or patient portal.
A balanced, liver-friendly diet supports your liver and helps manage weight and blood sugar. The same habits that support healthy blood sugar generally support liver health too.
Explore Liver DietThe Amsety Bar is a liver-friendly snack or meal replacement that can make it easier to eat well on busy days.
Explore Amsety Bars
COMMON QUESTIONS
A normal fasting glucose result is 70–99 mg/dL. Results from 100 to 125 mg/dL fall in the prediabetes range. A result of 126 mg/dL or higher on two separate occasions supports a diabetes diagnosis. A result below 70 mg/dL may point to low blood sugar (hypoglycemia). Ask your doctor what your result means given your health history, medicines, and other test results.
Yes, the two are closely linked. Insulin resistance, which raises blood glucose, is a key driver of MASLD (metabolic dysfunction-associated steatotic liver disease), the fat buildup in the liver tied to metabolic risk factors. Type 2 diabetes and insulin resistance are both counted as cardiometabolic risk factors. Fat in the liver plus at least one cardiometabolic risk factor establishes MASLD. A high fasting glucose result alone does not show liver damage. Your doctor looks at it together with liver blood tests and imaging. MASH is a more serious form of MASLD, in which fat buildup progresses to inflammation, tissue damage, and scarring (fibrosis).
You typically need at least 8 hours with no food or drink except water, usually overnight. Avoid sugary drinks and coffee during the fast. Confirm the exact fasting window with your doctor, since it can differ when other blood tests are drawn at the same visit.
No. One high reading does not confirm diabetes. Your doctor will usually repeat the test on another day or confirm it with a different test. Diabetes is diagnosed when fasting glucose is 126 mg/dL or higher on two different occasions. It can also be confirmed with an A1C of 6.5% or higher, or with an oral glucose tolerance test, in which glucose is 200 mg/dL or higher two hours after a special sugar drink. A random (non-fasting) result of 200 mg/dL or higher may suggest diabetes, but a fasting test must confirm it.
Fasting glucose shows your blood sugar at one moment, after you have fasted. HbA1c (also called A1C) shows your average blood sugar over the past two months. Both tests can help diagnose diabetes. Doctors often use them together for a fuller picture of blood sugar control. A1C is also one of the blood tests used when evaluating MASLD, alongside a lipid panel and liver function tests.
Medical disclaimer: LiverDirectory provides educational information and a directory of providers. It does not provide medical advice, diagnosis, or treatment. Always consult a licensed physician regarding any medical condition.
