You can check your A1c through a standard blood draw at a lab, a quick fingerstick at your doctor’s office, or an at-home test kit you buy over the counter. The test itself requires no fasting and no special preparation, making it one of the simplest blood tests available. Which method you choose depends on whether you need a baseline screening or are monitoring an existing diagnosis.
What the A1c Test Actually Measures
Glucose in your bloodstream attaches to hemoglobin, the protein inside red blood cells that carries oxygen. The more glucose circulating in your blood over time, the more hemoglobin gets coated. Since red blood cells live about three months before your body replaces them, the A1c test captures your average blood sugar over roughly the past 90 days. That makes it fundamentally different from a finger-prick glucose reading, which only tells you what your blood sugar is right now.
The result comes back as a percentage. A higher percentage means more of your hemoglobin has been sugar-coated, which means your blood sugar has been running higher on average.
Three Ways to Get Tested
Lab Blood Draw
A venous blood draw at a laboratory is the gold standard. Your doctor orders the test, a technician draws blood from your arm, and results typically come back within a day or two. Lab-based A1c assays have the tightest precision, with variation of less than 1% between repeated measurements. If your result will be used to diagnose diabetes or prediabetes for the first time, a lab draw is the most reliable option.
Point-of-Care Fingerstick
Many clinics and doctor’s offices now run A1c tests on-site using a fingerstick device. A nurse, medical assistant, or even your doctor pricks your finger, collects a small blood sample, and feeds it into a desktop analyzer. Results are ready in minutes, often before your appointment ends. These point-of-care devices correlate closely with lab results, though they tend to read about 0.2 percentage points lower on average. About 85% of fingerstick results fall within 0.4 percentage points of the lab value, which is accurate enough for routine monitoring.
At-Home Test Kits
Several FDA-cleared home A1c kits are sold at pharmacies and online, including options from Walgreens, PTS Diagnostics (marketed as TRUE+ A1C Now Self Check), and ReliOn. These kits use a fingerstick sample you collect yourself. Most provide results in about five minutes. Home kits are convenient for tracking trends between doctor visits, but they carry slightly more variability than clinical tests because the sample collection is less controlled. They work best as a supplement to, not a replacement for, lab testing.
No Fasting Required
Unlike a fasting glucose test, the A1c does not require you to skip meals or avoid food beforehand. You can eat and drink normally before the test. That said, your doctor may order other bloodwork at the same appointment, like a cholesterol panel, that does require fasting. If you’re unsure, ask your provider’s office when you schedule.
Certain medications can skew A1c results in either direction. Opioids and some HIV medications are known to cause falsely high or low readings. If you take any of these, let your doctor know so they can interpret the result in context or choose an alternative test.
What the Numbers Mean
The American Diabetes Association uses these ranges for diagnosis:
- Below 5.7%: Normal
- 5.7% to 6.4%: Prediabetes
- 6.5% or higher: Diabetes
Each percentage point translates to a concrete average blood sugar level. An A1c of 6% corresponds to an estimated average glucose of about 126 mg/dL. At 7%, that average rises to roughly 154 mg/dL. At 8%, it’s around 183 mg/dL. At 10%, you’re looking at an average near 240 mg/dL. The conversion formula is straightforward: multiply your A1c by 28.7, then subtract 46.7, and you get your estimated average glucose in mg/dL.
How Often to Test
The American Diabetes Association recommends testing at least twice a year if your blood sugar is stable and within your target range. If you’ve recently changed medications, adjusted your treatment plan, or aren’t hitting your goals, testing every three months makes more sense. Your doctor may also run interim checks between quarterly tests if your numbers are fluctuating significantly.
For people without a diabetes diagnosis who are simply screening, a single A1c test can establish your baseline. If the result falls in the prediabetes range, your doctor will typically recheck in six to twelve months to see if lifestyle changes are moving the number.
When A1c Results May Be Unreliable
Because the test depends on hemoglobin, anything that alters your red blood cells can throw off the reading. Iron-deficiency anemia, sickle cell trait, and other hemoglobin variants (including hemoglobin C, E, and D) can cause falsely high or low results depending on which laboratory method is used. Hundreds of hemoglobin variants exist, but these four are the most common sources of interference.
If your A1c result doesn’t match what your daily glucose readings suggest, or if you carry a known hemoglobin variant, your doctor can verify the lab’s testing method against a database maintained by the National Glycohemoglobin Standardization Program. In some cases, an alternative test like fructosamine, which measures sugar-coated proteins over a shorter two-to-three-week window, gives a more accurate picture.
Recent blood loss, blood transfusions, and pregnancy can also shorten the lifespan of your red blood cells and make the A1c read lower than your actual average sugar level. Kidney disease in later stages has a similar effect. In all these situations, your doctor may rely more heavily on direct glucose monitoring than on A1c alone.