Enter a fructosamine result in µmol/L and see the A1C it predicts, in percent and mmol/mol, together with the average glucose that A1C corresponds to. Or type an A1C to see the fructosamine level it maps to. It is built for anyone handed a fructosamine number instead of the A1C they are used to.
What is fructosamine?
Fructosamine is a blood test that measures how much glucose has attached itself to the proteins in your serum, mostly albumin. Those proteins are replaced within a few weeks, so the result reflects your average glucose over roughly the last one to three weeks. It is reported in micromoles per litre (µmol/L), a unit that means nothing to most people, which is why a conversion to the familiar A1C scale is the first thing anyone asks for.
A1C works the same way on a different protein: glucose attached to the hemoglobin inside red blood cells, which live about three months. Same idea, different carrier, different time window.
When is fructosamine used instead of A1C?
Mostly when A1C cannot be trusted, or is too slow. A review in the Cleveland Clinic Journal of Medicine lists the usual reasons:
- Hemoglobin variants (sickle cell trait among them) that interfere with some A1C methods.
- Anything that changes how long red blood cells live: anemia, recent blood loss or transfusion, kidney disease, some medicines. A1C then reads falsely high or low while fructosamine is unaffected.
- Rapid treatment changes, where a three-month test would lag: fructosamine shows the effect within weeks.
- Pregnancy, where glucose changes quickly, though the review notes its use there is limited.
Fructosamine has blind spots of its own. Because it rides on albumin, conditions that change albumin make it unreliable: nephrotic syndrome, advanced liver disease and protein-losing gut disease among them. If you wear a CGM, the sensor average and GMI cover the same short window without depending on any protein at all.
How the fructosamine to A1C conversion works
This calculator applies a population regression line published in 2003 (Cohen et al., Diabetes Care 2003): the authors measured A1C and fructosamine on the same blood sample in 153 people and fitted the line that best predicts A1C from fructosamine, A1C (%) = 0.017 x fructosamine (µmol/L) + 1.61, with a correlation of about 0.78. On that line a fructosamine of 317 µmol/L predicts an A1C of 7.0 percent and 375 µmol/L predicts 8.0 percent, the two worked examples the Cleveland Clinic review quotes.
Three honest caveats. The scatter around the line is substantial: the same study coined the term glycation gap for the difference between a measured A1C and the one predicted from fructosamine, and found that gap reproducible from visit to visit, so part of the difference is real biology, not noise. The line was fitted in people whose average A1C was around 8 percent, so it is least reliable at the extremes. And no clinical guideline endorses converting fructosamine to A1C for treatment decisions. Read the result as orientation: it tells you what the number means in a scale you know, not what your A1C would be.
Fructosamine to A1C conversion chart
Fructosamine from 200 to 500 µmol/L in steps of 25, with the A1C it predicts in percent and mmol/mol and the average glucose that A1C corresponds to on the ADAG line, all rounded the way the calculator rounds.
| Fructosamine (µmol/L) | A1C (%) | A1C (mmol/mol) | Average glucose (mg/dL) | Average glucose (mmol/L) |
|---|---|---|---|---|
| 200 | 5.0 | 31 | 97 | 5.4 |
| 225 | 5.4 | 36 | 109 | 6.1 |
| 250 | 5.9 | 41 | 121 | 6.7 |
| 275 | 6.3 | 45 | 134 | 7.4 |
| 300 | 6.7 | 50 | 146 | 8.1 |
| 325 | 7.1 | 54 | 158 | 8.8 |
| 350 | 7.6 | 59 | 170 | 9.5 |
| 375 | 8.0 | 64 | 182 | 10.1 |
| 400 | 8.4 | 68 | 195 | 10.8 |
| 425 | 8.8 | 73 | 207 | 11.5 |
| 450 | 9.3 | 78 | 219 | 12.2 |
| 475 | 9.7 | 82 | 231 | 12.8 |
| 500 | 10.1 | 87 | 243 | 13.5 |
What is a normal fructosamine level?
Reference ranges differ by laboratory and method, so the range printed next to your own result is the one that counts. As one example, Labcorp lists 205 to 285 µmol/L as its reference interval for healthy adults, and 228 to 563 µmol/L as the span it sees in poorly controlled diabetes. On the conversion line above, the top of that healthy range, 285 µmol/L, corresponds to an A1C of about 6.5 percent, which is a reminder of how approximate the line is: a lab A1C of 6.5 percent is the ADA diagnostic threshold, not a healthy value.
The formulas behind this page
- A1C (%) = 0.017 x fructosamine (µmol/L) + 1.61, the population regression of A1C on fructosamine in 153 people. Cohen et al., Diabetes Care 2003
- Fructosamine (µmol/L) = (A1C% - 1.61) / 0.017, the same line solved for fructosamine, which is how an A1C you type turns into a fructosamine level.
- A1C in mmol/mol = (A1C% - 2.15) x 10.929, the standard NGSP to IFCC conversion.
- Average glucose (mg/dL) = 28.7 x A1C - 46.7, the ADAG line, so the estimated A1C can be read in the units your meter or CGM uses. Nathan et al., Diabetes Care 2008
Have an A1C and want the average glucose behind it? Use our A1C calculator. Wearing a CGM? Our GMI to A1C calculator turns your sensor average into the A1C it predicts, with no protein in the way.
Frequently asked questions
What is a good fructosamine level?
There is no single target. For adults without diabetes, one large US laboratory lists 205 to 285 µmol/L as its reference interval, and every laboratory prints its own range on the report, so read the one next to your result. For people with diabetes, care teams think in A1C terms, which is what the conversion above is for: a fructosamine of about 317 µmol/L predicts an A1C near 7 percent. Your own goal is set with your care team, not by a range on a website.
How does fructosamine compare to A1C?
Both measure glycation, glucose attached to a protein, but on different carriers over different windows. A1C is glucose bound to hemoglobin inside red blood cells, which live about three months, so it reflects roughly the last two to three months. Fructosamine is glucose bound to serum proteins, mostly albumin, which turn over within weeks, so it reflects roughly the last one to three weeks. A few weeks after a treatment change, fructosamine has already moved while A1C is still catching up.
Is fructosamine equivalent to HbA1c?
No. The two correlate (r about 0.78 in the study behind this calculator), but they are different tests, and a regression line cannot recover what makes them differ. The difference between a measured A1C and the A1C predicted from fructosamine even has a name, the glycation gap, and the 2003 study that coined it found the gap reproducible from one visit to the next, so the two tests carry partly different information. Read a converted value as orientation, never as an A1C result.
What fructosamine level equals an A1C of 7?
About 317 µmol/L on the regression line this page uses, and about 375 µmol/L corresponds to an A1C of 8 percent, the two worked examples the Cleveland Clinic Journal of Medicine review quotes. Between them, roughly every 6 µmol/L of fructosamine is one tenth of an A1C point.
Why would a doctor order fructosamine instead of A1C?
Mostly when A1C cannot be trusted or is too slow. Hemoglobin variants and anything that changes how long red blood cells live (anemia, recent blood loss or transfusion, kidney disease, some medicines) make A1C read falsely high or low, while fructosamine is unaffected. It is also used to follow rapid treatment changes, where a three-month test would lag, and sometimes in pregnancy, where glucose changes quickly. Fructosamine has its own blind spots: conditions that change albumin, such as nephrotic syndrome, advanced liver disease or protein-losing gut disease, make it unreliable in turn.
Can this calculator replace a lab A1C test?
No. It applies a published regression line, derived in 153 people with substantial scatter around it, and no clinical guideline endorses converting fructosamine to A1C for decisions. Use the result to understand a fructosamine report in familiar terms, and rely on the laboratory for diagnosis and treatment.
More free tools
- Blood Sugar Converter: mmol/L to mg/dL and Back
- A1C Calculator: Convert A1C to Average Glucose
- Time in Range Calculator
- GMI to A1C Calculator: Estimate A1C from Your CGM Average
- Blood Glucose Log: Free Printable Log Sheet (PDF)
This tool is for education only. It is not medical advice, it does not replace laboratory testing, and it must never be used for insulin dosing or other treatment decisions. Always work with your healthcare team. See our full medical disclaimer.
