Getting tested for type 2 diabetes starts with a simple blood draw at your doctor’s office or a lab. There are four standard tests used for diagnosis, most take less than a day, and preventive screening is covered at no cost by Medicare and most insurance plans. You can request testing from your primary care provider even if you have no symptoms.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends screening for prediabetes and type 2 diabetes in adults aged 35 to 70 who are overweight or obese (a BMI of 25 or higher). This starting age was recently lowered from 40 to 35. If you fall in that range and haven’t been tested, it’s worth asking your doctor at your next visit.
Screening may start even earlier if you’re from a population with higher diabetes rates, including Black, Hispanic/Latino, American Indian/Alaska Native, or Native Hawaiian/Pacific Islander communities. For Asian Americans, screening is recommended at a lower BMI threshold of 23. A family history of diabetes, a history of gestational diabetes, or conditions like polycystic ovary syndrome can also prompt earlier testing regardless of age.
You don’t need symptoms to request a test. Type 2 diabetes often develops gradually over years, and many people have elevated blood sugar long before they notice anything unusual. That’s exactly why routine screening matters.
The Four Diagnostic Tests
A1C Test
The A1C test measures your average blood sugar over the past two to three months. It requires a standard blood draw but no fasting, so you can eat and drink normally beforehand. Results are reported as a percentage:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
Because it reflects a longer window of blood sugar control rather than a single moment, the A1C is one of the most commonly used screening tests. Certain conditions, including sickle cell trait and some anemias, can affect its accuracy, so your doctor may choose a different test if those apply to you.
Fasting Plasma Glucose Test
This test measures your blood sugar after you’ve fasted for at least eight hours (water is fine). It’s typically scheduled first thing in the morning so the fasting period overlaps with sleep. Results are measured in mg/dL:
- Normal: 99 or below
- Prediabetes: 100 to 125
- Diabetes: 126 or above
The fasting glucose test is straightforward and widely available. If your result comes back in the diabetes range, a second test on a different day is typically needed to confirm the diagnosis.
Oral Glucose Tolerance Test
The oral glucose tolerance test (OGTT) is more involved. You fast for at least eight hours, then have your blood drawn. After that first draw, you drink a syrupy solution containing 75 grams of sugar. Your blood is drawn again two hours later to see how efficiently your body processed the glucose. The two-hour results break down like this:
- Normal: below 140 mg/dL
- Prediabetes: 140 to 199 mg/dL
- Diabetes: 200 mg/dL or above
This test takes longer and requires you to stay at the lab or clinic for the full two hours. It’s particularly useful for detecting prediabetes and is sometimes used when other test results are borderline. The sugar drink can taste very sweet and occasionally causes nausea, but most people tolerate it without problems.
Random Plasma Glucose Test
A random glucose test can be done at any time, without fasting. It’s not typically used for routine screening, but if your blood sugar happens to come back at 200 mg/dL or higher and you’re experiencing classic symptoms like excessive thirst, frequent urination, or unexplained weight loss, that combination is enough for a diabetes diagnosis.
How to Prepare
Preparation depends on which test your doctor orders. For the A1C, there’s nothing special to do. For the fasting glucose or oral glucose tolerance test, you’ll need to avoid all food and drinks except water for at least eight hours before your appointment. Scheduling a morning appointment makes this easiest.
Let your doctor know about all medications and supplements you take before the test. Some can affect blood sugar readings, and your provider may ask you to temporarily stop certain ones. Maintain your normal activity level for at least three days leading up to the test. Don’t do an unusually intense workout right before, as heavy exercise can temporarily alter blood sugar.
What Happens After Your Results
If your first test comes back in the diabetes range, your doctor will generally want a second test to confirm. This might be a repeat of the same test on a different day or a different type of test altogether. A single elevated result isn’t usually enough for a formal diagnosis unless your symptoms are obvious and your blood sugar is very high.
If your results fall in the prediabetes range, that’s actually useful information. Prediabetes means your blood sugar is elevated but hasn’t crossed the diabetes threshold yet. At this stage, moderate changes to diet and physical activity can significantly reduce the risk of progressing to type 2 diabetes. Your doctor will likely recommend retesting in one to three years to monitor any changes.
Normal results don’t mean you never need testing again. If you have risk factors, periodic rescreening every three years is a reasonable schedule. Your doctor can adjust that based on your individual situation.
At-Home A1C Test Kits
Over-the-counter A1C kits are available at pharmacies and online. They use a finger prick instead of a full blood draw and give results at home. However, accuracy varies significantly between brands. A University of Florida study of 219 people compared several home kits against standard lab results. To meet the accepted accuracy benchmark, home test results need to land within 5% of the lab value in at least 90% of samples.
One kit (Home Access) hit that benchmark in 82% of samples, which is close but still below the standard. Two others, A1cNow+ and CoreMedica, met it in only 46% and 29% of samples. That level of inaccuracy means a home kit might tell you you’re normal when you actually have prediabetes, or vice versa. Home kits can be a reasonable first step if you want a general sense of where you stand, but a lab test through your doctor is far more reliable for an actual diagnosis.
Cost and Insurance Coverage
Medicare Part B covers up to two diabetes screenings per year at no cost to you, as long as your provider determines you’re at risk. Most private insurance plans also cover preventive diabetes screening with no copay under the Affordable Care Act’s preventive care provisions, which require coverage of services recommended by the U.S. Preventive Services Task Force.
If you’re uninsured, community health centers and local health departments often offer low-cost or free diabetes screening events. The blood tests themselves are relatively inexpensive even without insurance, typically ranging from $10 to $50 for a fasting glucose or A1C at an independent lab. Some pharmacies also offer point-of-care A1C testing at a walk-in price, though the same accuracy concerns with non-lab testing apply.