Lab results explained
Diabetes Blood Tests Explained: HbA1c and Fasting Glucose
Two blood tests do most of the work in checking for prediabetes and diabetes: HbA1c, which reflects your average blood sugar over about three months, and fasting glucose, a snapshot of one morning. This page explains how they fit together. Each test has its own detailed guide.
Tests in this panel
Why two tests?
HbA1c and fasting glucose look at blood sugar in different ways, so they do not always agree. HbA1c smooths out day-to-day swings, while fasting glucose shows how well your body keeps sugar in check overnight. Either can be used for screening, and together they give a fuller picture.
Screening and diagnosis thresholds
Diabetes is usually diagnosed at an HbA1c of 6.5% (48 mmol/mol) or higher, or a fasting glucose of 126 mg/dL (7.0 mmol/L) or higher. The prediabetes range is an HbA1c of 5.7 to 6.4% (39 to 47 mmol/mol) or a fasting glucose of 100 to 125 mg/dL (5.6 to 6.9 mmol/L). Some countries use slightly different prediabetes cut-offs.
Why one result is confirmed
Unless you have clear symptoms of high blood sugar, a single abnormal result is normally repeated before a diagnosis is made, either with the same test on another day or with the other test. Illness, stress and some medicines can push glucose up for a while.
When the two tests disagree
Anything that changes red blood cells, such as anemia, recent blood loss or transfusion, some hemoglobin variants, kidney disease or pregnancy, can make HbA1c read higher or lower than your true average. In those cases clinicians lean more on glucose tests, including an oral glucose tolerance test.
Other tests you might see
An oral glucose tolerance test measures blood sugar two hours after a sweet drink. People living with diabetes also tend to have kidney checks (eGFR and urine albumin), a lipid panel and regular eye and foot exams, because diabetes affects blood vessels throughout the body.
Frequently asked questions
Do I need to fast for an HbA1c test?
No. HbA1c reflects the past two to three months, so a recent meal does not change it. Fasting glucose does need at least eight hours without food or drinks other than water.
Can prediabetes be reversed?
Often, yes. Losing a modest amount of weight if you carry extra, being active most days and eating fewer refined carbohydrates bring blood sugar back into the normal range for many people. Rechecking at least once a year shows whether it is working.
How often should blood sugar be checked?
Many guidelines suggest screening adults from age 35, or earlier with risk factors such as excess weight, a family history of diabetes or diabetes in a past pregnancy, and repeating every three years if results are normal. People living with diabetes usually have HbA1c checked every three to six months.
What is a normal fasting blood sugar?
A fasting glucose below 100 mg/dL (5.6 mmol/L) is usually normal. Levels below 70 mg/dL (3.9 mmol/L) are low and, with symptoms such as shakiness, sweating or confusion, need prompt attention.
Follow your blood sugar over time
Add your results to VHT to see HbA1c and glucose side by side across the years, and ECHNA, your AI health assistant, explains what changed in plain language.
