Since prediabetes rarely comes with obvious symptoms, blood tests are the primary way doctors identify it. There are three main tests used for screening, and each one measures your blood sugar in a slightly different way. Understanding these tests and what your results mean can help you take the right steps early.
Fasting Blood Sugar Test (Fasting Plasma Glucose / FPG)
This is one of the most common screening tools. It measures your blood sugar after you have gone at least 8 hours without eating or drinking anything other than water. You typically take this test first thing in the morning.
Here is how to read your results:
- Below 100 mg/dL: Normal
- 100 to 125 mg/dL: Prediabetes
- 126 mg/dL or higher: Diabetes
A1C Test (Hemoglobin A1C / HbA1c)
The A1C test gives you a bigger picture. Instead of measuring your blood sugar at a single point in time, it shows your average blood sugar levels over the past two to three months. It works by measuring the percentage of hemoglobin (a protein in your red blood cells) that has glucose attached to it.
Here is what the numbers mean:
- Below 5.7%: Normal
- 5.7% to 6.4%: Prediabetes
- 6.5% or higher: Diabetes
One advantage of the A1C test is that you do not need to fast before taking it, which makes it more convenient for many people.
Oral Glucose Tolerance Test (OGTT)
This test is a bit more involved. It starts with a fasting blood sugar measurement. Then you drink a sugary solution containing 75 grams of glucose, and your blood sugar is tested again two hours later. This shows how well your body handles a large dose of sugar.
The two-hour results break down like this:
- Below 140 mg/dL: Normal
- 140 to 199 mg/dL: Prediabetes
- 200 mg/dL or higher: Diabetes
When Should You Get Tested?
The American Diabetes Association recommends screening for prediabetes if you are 45 or older, regardless of other factors. If you are younger than 45 but are overweight and have one or more additional risk factors (family history, physical inactivity, history of gestational diabetes, PCOS, or belong to a higher-risk ethnic group), you should also ask your doctor about screening.
Do not wait until you feel something is wrong. Getting tested is quick, straightforward, and it could be the single most important thing you do for your long-term health.
How Often Should You Retest?
If your results come back normal, retesting every three years is generally recommended. If you are diagnosed with prediabetes, your doctor will likely want to monitor your levels more frequently, usually every year, to track your progress and adjust your plan as needed.