Calculadora A1C - Hemoglobina A1C a Glucosa en Sangre Promedio

Haemoglobin A1c (HbA1c) reflects the proportion of haemoglobin that has become glycated, which rises with average blood glucose over the preceding two to three months. Because red blood cells survive roughly 120 days, a single A1c measurement summarises glucose control over that whole window rather than at one moment, which is why it is used both to diagnose diabetes and to track treatment. This calculator converts between A1c and estimated average glucose (eAG), the same average expressed in the units a home glucose meter reports.

La fórmula

eAG (mg/dL) = 28.7 x A1C - 46.7
eAG (mmol/L) = 1.59 x A1C - 2.59

• A1C = haemoglobin A1c as a percentage (NGSP units)
• eAG = estimated average glucose over roughly the previous 8 to 12 weeks

Derived from the A1c-Derived Average Glucose (ADAG) study, which fitted the relationship using continuous glucose monitoring and frequent fingerstick data from 507 participants across 11 centres (Nathan et al., Diabetes Care, 2008). The linear fit is the basis of the eAG values reported alongside A1c by most laboratories.

How the calculation works

Glucose in the bloodstream attaches to haemoglobin without an enzyme, in proportion to how much glucose is present and for how long. The percentage of haemoglobin carrying that attachment is what an A1c assay measures. Because the attachment is essentially irreversible for the life of the red cell, A1c integrates glucose exposure across the cell population, weighted towards the most recent weeks: roughly half the result reflects the previous 30 days, with the remainder spread over the two months before that.

The conversion to estimated average glucose is a straight line fitted to measured data, not a derivation from first principles. That matters for how much precision to read into it. The ADAG investigators reported the relationship as strong at the group level but with meaningful individual spread, so a person with an A1c of 7 percent has an average glucose close to 154 mg/dL on average, while any individual with that A1c may sit somewhat above or below.

How to read your result

The diagnostic thresholds below are those used by the American Diabetes Association and adopted, with minor wording differences, by most national guidelines. Diagnosis of diabetes from A1c alone normally requires either two abnormal results or one abnormal result confirmed by a second test, because a single measurement can be affected by assay variation and by the conditions listed under limitations.

• Two unit systems are in use. The percentage (NGSP) scale is standard in the United States; the mmol/mol (IFCC) scale is standard across much of Europe. They describe the same measurement.
• Treatment targets are individualised. A target below 7 percent is common for non-pregnant adults, but a less strict target is often appropriate for older adults, people with a long duration of diabetes, or anyone at high risk of hypoglycaemia.

Why A1c and daily meter readings can disagree

A frequent source of confusion is an A1c that seems inconsistent with the numbers on a home meter. Usually the explanation is sampling: meter readings are typically taken fasting or before meals, which are the lowest points of the day, while A1c reflects the entire 24-hour curve including post-meal peaks. Someone whose fasting readings look acceptable but whose glucose rises steeply after eating will see an A1c higher than their meter log suggests.

The reverse pattern, an A1c lower than expected, more often points to something affecting the red cells themselves rather than to better control. Anything that shortens red cell survival gives glycation less time to accumulate and pulls A1c down independently of glucose. This is why guidelines advise interpreting A1c alongside, not instead of, direct glucose measurement when the two disagree.

Limitaciones

• A1c is unreliable in any condition that alters red blood cell lifespan. Haemolytic anaemia, recent significant blood loss, recent transfusion, and treatment with erythropoietin all lower A1c independently of glucose control; iron deficiency anaemia and asplenia can raise it.
• Several haemoglobin variants, including HbS, HbC, HbE and HbD traits, interfere with some assay methods. Laboratories use variant-tolerant methods where this is known, but an unexpected result in someone of African, Mediterranean or Southeast Asian ancestry warrants asking which method was used.
• A1c is not recommended for diagnosing diabetes in pregnancy, in children with suspected type 1 diabetes, or in anyone with symptoms of rapid-onset hyperglycaemia, because the two-to-three-month averaging is too slow to reflect an acute change.
• Chronic kidney disease, advanced liver disease and HIV treatment with certain agents can all shift A1c away from the underlying glucose average.
• The eAG conversion is a population average. Individuals glycate haemoglobin at slightly different rates, so two people with identical average glucose can have A1c values that differ by a few tenths of a percent.
• This tool converts and interprets a value you already have. It cannot measure A1c, and it is not a substitute for a laboratory test ordered and interpreted by a clinician.

Preguntas frecuentes

What A1c level means diabetes?

An A1c of 6.5 percent (48 mmol/mol) or above is the diagnostic threshold for diabetes. Guidelines require confirmation, either a second A1c or a second type of test such as fasting glucose, before the diagnosis is made, unless the person has clear symptoms of hyperglycaemia.

How quickly can A1c change?

Because A1c averages roughly three months of glucose exposure, a change in treatment or diet usually takes about six to twelve weeks to show up meaningfully, and about three months to be fully reflected. Repeating the test sooner than three months rarely gives a clean read on whether a change is working.

What is estimated average glucose (eAG)?

eAG expresses the same information as A1c in the units a glucose meter uses, mg/dL or mmol/L. It is calculated from A1c using a linear equation from the ADAG study and is intended to make the result easier to relate to day-to-day readings.

Can I be diagnosed from a single A1c test?

Normally no. Standard practice is to confirm an abnormal A1c with a repeat test, because assay variation and red cell conditions can shift a single result. A person with unmistakable symptoms of hyperglycaemia and a markedly elevated glucose may be diagnosed without waiting for confirmation.

Does A1c show my blood sugar swings?

No. A1c is an average and cannot distinguish steady glucose from wide swings that happen to average to the same value. Glucose variability is assessed with a meter log or continuous glucose monitoring, and matters clinically because swings carry hypoglycaemia risk that an average hides.

Referencias

1. National Institute of Diabetes and Digestive and Kidney Diseases. The A1C Test and Diabetes.
2. Nathan DM et al. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care, 2008.
3. Eyth E, Naik R. Hemoglobin A1C. StatPearls, NCBI Bookshelf.
4. Centers for Disease Control and Prevention. All About Your A1C.