How to track your A1c over time

Hemoglobin A1c is one of the most tracked lab tests there is. Anyone with diabetes or prediabetes sees it a few times a year, and it shows up on plenty of routine physicals too. It is also one of the tests that most rewards keeping a history. A single A1c tells you where you stand today. A run of them tells you which way you are heading, and whether the changes you made are working.

What A1c measures

Sugar in your blood sticks to hemoglobin, the protein inside red blood cells. The more glucose there is, the more of it attaches. Red cells live about three months, so the share of hemoglobin carrying glucose reflects your average blood sugar over roughly the past two to three months. Recent weeks count for more than older ones.

That is what makes A1c different from a glucose reading. A fingerstick or a fasting glucose is a snapshot of one moment. A1c is a long average, so it does not move much from one day to the next, and it does not show the highs and lows that make up the average.

The numbers on the report

In the United States, A1c is reported as a percentage. The cutoffs are the same at every lab, because they come from clinical guidelines rather than from each lab’s own population. The CDC lists them as:

A diagnosis of diabetes is usually confirmed with a second test, not made from one result.

For people who already have diabetes, the number that matters is the goal set with their clinician. The American Diabetes Association’s Standards of Care treat below 7% as a reasonable goal for many adults, and set it higher or lower depending on age, other conditions, and the risk of low blood sugar. If your report prints a range of “4.0–5.6”, that is the normal range, not necessarily your goal. HealthViewer and most spreadsheets let you chart against your own target instead.

Percent and mmol/mol

Much of the world reports A1c in mmol/mol, the IFCC unit, instead of percent. If you have results from a lab abroad, or from a health system that uses IFCC units, your history will mix the two. They are not interchangeable: 48 mmol/mol is 6.5%, not 48%. The NGSP conversion is:

mmol/mol = (10.93 × %) − 23.5

Convert everything to one unit before you chart it, or the line will jump by a factor of seven at the switch.

Estimated average glucose

Some reports also print an estimated average glucose (eAG) in mg/dL. It is not a separate measurement. It is calculated from the A1c with a formula from the ADAG study:

eAG (mg/dL) = 28.7 × A1c − 46.7

So an A1c of 7% corresponds to an average of about 154 mg/dL. Because eAG is a direct calculation from the A1c, tracking both adds nothing. Track the A1c.

How often it is tested

A1c moves slowly, so testing more often than every three months tells you little. The usual schedules are:

• Diabetes, not yet at goal or after a treatment change: about every three months.
• Diabetes, stable and at goal: at least twice a year.
• Prediabetes: every one to two years, according to the CDC.
• Normal result: on a schedule your clinician sets based on age and risk.

That means even a well-tracked A1c history has only two to four points a year. Every one of them is worth keeping, and a result from five years ago at another clinic is often the most useful baseline you have. If yours are spread across several portals, How to get all of your medical records covers requesting the older ones.

What counts as a real change

Every A1c result has some noise in it, from the test itself and from ordinary day-to-day variation. A change of 0.1 or 0.2 points between two draws is usually not worth reading into. A change of half a point or more, or several results moving the same way, is a different story.

A few questions help sort it out:

• Is the move bigger than your usual spread? If your last five results ranged from 5.8 to 6.1, a 6.0 is not news. A 6.6 is.
• Did more than one result move? One high value followed by a return to your usual level is often noise. Three in a row climbing is a trend.
• What changed in the three months before the draw? Not the week before. A1c averages over months, so a change you made two weeks ago will barely show yet.

That last point matters when you are checking whether something worked. A new medication, diet, or exercise routine needs about three months before A1c fully reflects it. A result six weeks in will show part of the effect. Did the medication actually do anything? covers reading a before-and-after fairly.

When A1c can mislead

A1c assumes your red blood cells live a normal lifespan and carry ordinary hemoglobin. When that is not true, the number can be off in either direction, even when your blood sugar has not changed. The NGSP and the CDC list the main causes:

• Iron deficiency anemia tends to push A1c up, and treating it with iron can bring A1c down without any change in blood sugar.
• Blood loss, transfusions, and conditions that shorten red cell life, such as hemolytic anemia, push it down.
• Hemoglobin variants, including sickle cell trait, can interfere with some test methods. The effect depends on the variant and the lab’s method.
• Kidney failure, liver disease, pregnancy, and some medicines can also affect it.

If one of these applies to you, a sudden jump or drop in your A1c may be about your blood rather than your blood sugar. That is worth raising with your clinician, who may use glucose monitoring or another test alongside A1c. It is also worth a note in your history, so the result makes sense when you look back at it.

What to record with each result

For each A1c, keep:

A1c also goes by several names: Hemoglobin A1c, HbA1c, A1C, glycated hemoglobin, and glycohemoglobin. Pick one and use it everywhere, or your history will split into several short lines.

Charting it

A simple line chart is enough. A few things make it honest:

• Space points by date. Results three months apart and results two years apart should not look evenly spaced.
• Draw your goal, not just the lab range. If your target is below 7%, a chart shaded at 4.0–5.6 makes every point look like a failure.
• Mark medication changes, with the three-month lag in mind when you read what came after.
• If you use a CGM or a glucose meter, chart its average glucose on the same timeline. The daily readings fill in the months between A1c draws, and A1c confirms whether the meter’s picture holds up.

How to track your lab results over time has the general method for any test. A1c is one of the easiest to start with, because there are few results and the units are simple.

Tracking A1c in HealthViewer

HealthViewer is a lab results tracker that runs on your own computer. It imports A1c results from lab report PDFs, MyChart downloads, and direct connections to your health system, and files Hemoglobin A1c, HbA1c, and A1C under one test. Results in mmol/mol are converted to percent so they share one chart.

In Trends, you can chart your A1c with medication starts and stops marked on the timeline, and set your own target range in the Test Catalog so the chart shades your goal instead of the lab’s normal range. If you use a Dexcom CGM, a Clarity export imports as daily average glucose and time in range, which you can chart next to your A1c.

Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.

This post is general information, not medical advice. Talk to your clinician about your A1c goal and before changing any treatment.