What is A1c? and what does it really mean?
If you’ve been a part of the diabetes community for even a short time, you’ve probably heard of the A1C test. You may already understand that it measures your average blood glucose over the past 2-3 months. But how does it do this? Why is it sometimes referred to as Hemoglobin A1c, or even glycated hemoglobin? And when is this “test” not a test?
Hemoglobin is the protein inside red blood cells that carries oxygen. When your blood glucose level is elevated, those excess glucose molecules stick to the hemoglobin, which is now becomes “glycated hemoglobin;” that is, hemoglobin with glucose attached. I picture it like a plain donut dusted with sugar crystals, but instead its “sugared” hemoglobin. The higher the level of glucose in the blood, the more of this glycated hemoglobin is formed.
Once the glucose binds to the hemoglobin, it remains there for the life of the red blood cell, about 2-3 months. The A1c blood test measures the percentage of red blood cells that contain this hemoglobin with glucose attached. The higher that blood glucose has consistently been over the past few months, the more red blood cells there will be with glucose stuck to them, which will result in a higher A1C number.
The Short Version:
A red blood cell lives for about three months. During that time, hemoglobin (a part of red blood cells) picks up sugar from the blood. If blood glucose is often high, more sugar will stick to the hemoglobin, resulting in a high A1c.
How is an A1c Test Performed?
A blood sample can be taken from the fingertip or from a vein in the arm. If in doubt, ask your child’s diabetes team what kind of sample is needed and where to go to have it done. If the most appropriate method is to have a blood sample taken from a vein, you may choose to use a topical anesthetic to numb the skin (such as EMLA™ cream, Ametop Gel™, Maxilene 4™or Maxilene 5™). If you use a numbing cream, keep in mind that it may shrink the vein, making it harder for the lab tech to find it. Maxilene™ is more minimally vasoactive than EMLA.™ Translation: Maxilene is less likely to cause the vein to shrink and therefore will make it easier than EMLA for the lab technician to draw a sample.
Tips from the Trenches
I have preferred different approaches at different times in my son’s life: when he was very little, I was uncomfortable with the thought of obtaining a blood sample via a needle in his arm –he was so little, and I felt like he got enough needles as it is, so I wanted to spare him this one by opting for a finger-prick to obtain a sample. For a time, that was the right decision for our family. Lately, we have opted for obtaining a blood sample from a vein in his arm, and have found that method more efficient, without much more reaction from my son. Currently that is the right decision for our family – but every family is different. Also, for a venous blood sample, we have used EMLA cream at times and we have gone without it at times, and have found that it may actually make it harder for the technician to locate a vein efficiently, so currently we do not use EMLA at blood test time.
Tips from the Trenches
I too have preferred different approaches over the years for my son. When he was very little, we always used EMLA but chose to get his blood work done at the Children’s Hospital where they were experts at dealing with “little” veins. It was easier for them to find the vein if I had my son drink lots of fluids about 1 hour prior to the test. When he grew bigger, we still used EMLA but we were able to use the local lab as long as he drank a lot prior to the blood test. We then transitioned to not numbing the skin, still drinking lots and a small reward after. This method was used for years, with my son greatly looking forward to the “reward” after the blood test and thus not dreading the actual test so much.
In many cases, the choice of method is yours. But here are some additional things to consider:
- The finger-poke is not necessarily less painful – the lancet used is bigger than the one your child uses to check blood glucose daily, as a larger sample is needed to arrive at an accurate A1c. Also, the finger often has to be squeezed quite firmly to obtain an adequate sample.
- Not every lab has the materials in stock that are needed to do a finger-poke A1c test (although we have had pretty good luck with the lab at the Alberta Children’s Hospital).
- Drawing blood from a vein is more efficient, so the overall fear-factor may actually be reduced by using this method.
- If other blood tests are needed (such as a thyroid test), a blood sample will need to be drawn from a vein anyway, so you may just opt to have both tests done from that sample.
- If a lab to meter comparison is needed, a blood sample will need to be drawn from the vein, as a very large amount of blood is required and it is very challenging to obtain this much from a finger-poke. However, you (the parent) may provide the lab-to-meter-comparison sample (rather than your child), if you prefer, and then your child only has to provide the finger-poke sample for the A1c test.
Tips from the Trenches
In the end, no matter the method, drawing blood for lab blood work is, for me, still one of the hardest parts of parenting a child with diabetes. I've always had a bit of a needle-phobia, so it’s real challenge for me emotionally, even though my son copes quite well and shows little reaction or pain. So in terms of the division of responsibility that my husband and I have worked out, taking our son for blood work falls on his list. (Although if that is not feasible for a given visit, I will do what needs to be done.) For your family, consider who would be the best choice to accompany your child for blood tests. Who is more comfortable with the process of drawing blood, and would therefore provide a calm model for your child? If neither spouse is comfortable with this task, or if you are a single parent and find this process very difficult, consider asking a close family member or friend to accompany you and your child for support. If this process causes extreme distress for your child, you may consider contacting a psychologist or behaviourist for strategies to reduce this distress.
How Often Is This Test Done?
The A1c test is usually done every three months.
What Should the A1c Result Be?
The normal range (for persons who do not have diabetes) at an Alberta Health Services lab is 4.3-6.1 %. This range may vary between labs. Most people with type 1 diabetes do not have the same “normal” A1c that those with a fully functional pancreas do. (Though some have achieved this, showing it's not impossible.) Speak with your diabetes team about an appropriate target A1c for your child.
Research shows that lower A1c levels can greatly decrease the risk of long term complications (such as nerve, kidney and eye damage)¹. In fact, estimates are that even a 0.5% reduction in A1c results in a significantly lower risk of future complications. If your child has a high A1c, you and your child’s diabetes team will develop an action plan to help lower it. On the other hand, it is important to keep in mind that efforts to lower your child’s A1c must be balanced with safety (in terms of low blood glucose). This is particularly important for younger children and/or those who are not aware when they are experiencing a low.
The International Society for Pediatric and Adolescent Diabetes (ISPAD) recommends in the 2018 Clinical Practice Consensus Guidelines²:
"a target HbA1c of less than 7.0% for children, adolescents, and young adults ≤25 years who have access to comprehensive care."
They go on to say that:
"A higher HbA1c goal (still less than 7.5% in most cases) may be appropriate when a child cannot articulate their low symptoms, do not detect their lows (hypoglycemic unawareness), has a history of severe lows, does not have access to analog insulins, advanced insulin dleivert technology (such as an insulin pump) or CGM, is not able to regularly check BG (for example, for families who cannot afford BG meter supplies, or in countries where meters and testing supplies are not readily available."
"A lower goal (6.5%) or 47.5 mmol/mol may be appropriate if achievable without excessive hypoglycemia, impairment of quality of life, and undue burden of care... (also ) a lower goal may be appropriate during the honeymoon phase."
ISPAD emphasizes that the targets outlined are intended as guidelines, which are based on clinical studies and expert opinion, as “no strict evidence-based recommendations are available” for blood glucose targets. "For children, adolescents, and young adults aged ≤25 years we recommend individualized targets, aiming for the lowest achievable HbA1c without undue exposure to severe hypoglycemia balanced with quality of life and burden of care”.
The Canadian Diabetes Association Clinical Practice Guidelines 2018 are slightly more conservative, recommending an A1c of 7.5% or less for children and teens under the age of 18 years³. They further recommend that "aggressive attempts should be made to (safely) reach the recommended glycemic target, while minimizing the risk for severe or recurrent hypoglycemia. Treatment targets should be tailored to each child, taking into consideration individual risk factors for hypoglycemia."
How does this compare to previous Clinical Practice Guidelines? The last edition (2013)³ broke down the recommendations according to age: a higher threshold back then for children under 6 (<8%), and a tighter A1C recommendation then for teens 13-18 years old (≤7.0%). The current recommended A1C of 7.5% or less for all ages of children and teens represents a shift toward individualized targets, which is similarly reflected in the ISPAD guidelines.
Extra Caution for Young Children
The 2018 Clinical Practice Guidelines³ point out that "in children <6 years of age, particular care to minimize hypoglycemia is recommended because of the potential association in this age group between severe hypoglycemia and later cognitive impairment (15)." However, they also highlight the results from a large multicentre observational study, which "found that glycated hemoglobin (A1C) targets of ≤7.5% can be safely achieved without an increase in the risk of severe hypoglycemia in children less than 6 years of age. (11)"
What can be done if A1C is too high?
From the Diabetes Canada's 2018 guidelines: "Children with persistently poor glycemic control (e.g. A1C >10%) should be assessed with a validated tool by a specialized pediatric DHC team for comprehensive interdisciplinary assessment and referred for psychosocial support as indicated. Intensive family and individualized psychological interventions aimed at improving glycemic control should be considered to improve chronically poor metabolic control."³ In other words, your family may be facing some obstacles that make it difficult to meet the recommended A1C targets; in this case, the purpose of the diabetes care team is to support and guide your family through those obstacles.
How Does A1c Relate to Average Blood Glucose?
The A1c number (expressed as a percentage) reflects the average blood glucose over the previous three months as follows:
A1c Conversion Chart from the Canadian Clinical Practice Guidelines, 2018³:
Correlation between A1C and estimated mean glucose values
|A1C values (%)||5.5–6.5||6.5–6.9||7.0–7.4||7.5–7.9||8.0–8.5|
|Estimated mean glucose (mmol/L)||6.2–7.7||7.8–8.5||8.6–9.3||9.4–10.1||10.2–10.9|
From this chart, average blood sugar is expressed as a range. For example, we can see that an A1C result of 6.0 relates to an estimated average (mean) glucose of somewhere between 6.2 and 7.7 mmol/L; an A1C of 7.0 relates to an average glucose between 8.6 and 9.3 mmol/L; and an A1C of 8.0 corresponds to average blood glucose of 10.2 to 10.9 mmol/L.
This same relationship between A1C and average blood glucose, expressed in another way:
Based on the above chart, if the result of your child’s A1c test was 7.5% (the recommended upper limit), his average blood glucose over the past 3 months was approximately 8.6. If the result of your child’s A1c test was 13.0% (a result higher than the CDA-recommended upper limit), his average blood glucose over the past 3 months was approximately 18.1.
If your child’s latest A1c result does not appear in the above table, an estimate may be calculated via the following formula:
[A1c (%) x 1.59] – 2.59 = average Blood Glucose (in mmol/L)
Using this formula, an A1c result of (ex) 8.4 represents an average blood glucose of [ 8.4 x 1.59 ] – 2.59 = 10.8 mmol/L.
Check out this handy A1C converter from Juicebox Podcast / Arden's Day - just plug in your A1C and the conversion calculator will give you an estimate of average blood glucose. Plus you can convert mmol/L (the units used to measure blood glucose in Canada) to mg/dL (the units used to measure blood glucose in the United States) and vice versa.
The Significance of A1c Results
The “take home” lesson about A1c testing is that lower is better (within the boundaries of safety regarding hypoglycemia). However, it is important to interpret A1c within the appropriate context.
First, it’s important to note that the A1c value is an average, and as such, does not take into account the range of blood glucose readings which contributed to a given result. That is, returning to the example above, an A1c of 7.0% suggests an average blood glucose of 8.6 (from the A1c Conversion Chart above). This value may be obtained by spending all of the time right at 8.6 (highly improbable in real-life, but theoretically useful for this example); it may also be obtained by spending half of the time at 2.6 (in a hypoglycemic state), and half of the time at 14.6 (in a hyperglycemic state). Therefore, to get a more complete picture of how well-controlled blood glucose is, we need to also consider other data measures, such as the maximum and minimum blood glucose readings, the percentage of readings which fall in the target blood glucose range, and the frequency of low blood glucose readings.
Further, if your child’s A1c is already within the recommended range and everyone is busting their butts to lower it another tenth of a point, you may want to consider whether the cost of achieving this goal is worth the benefit of a very-slightly-lower A1c. Our constant efforts to achieve lower and lower A1c’s may communicate to our kids that, no matter how hard they work and no matter how good it is, it will never be good enough. If this is the message your child is getting, it may be worthwhile to add their emotional health into the cost-benefit equation.
Finally, just as with the results of blood glucose (finger stick) checks, it’s helpful to talk about A1c results as being “above”, “within” or “below” recommended levels, as opposed to being “bad” or “good”. Every A1c result is a valuable result, as it gives us information about how we may (or may not) need to change our behaviour.
Tips from the Trenches
When is a test not a test?
When I cheered out loud for a lower-than-last-time A1c result, the endocrinologist asked me, “You realize it’s not a test, don’t you?” But to me, it had always felt like a test: Did I “pass” as a parent? Was I doing enough for my son’s glycemic control? Although it’s tempting to personalize the result, it’s important to remember that the A1c test is a test of your child’s blood; it is not a test of you as a parent, nor of your child as a person. What it is, however, is valuable information to guide your/your child’s ongoing decisions and goals about his diabetes care. Further, if the result is high, this may indicate that you (and your child, as age-appropriate) have important work to do to improve blood glucose control. If the result is significantly lower than recommended, that may be a sign that he is having undetected lows. Either way, it’s a good idea to talk with your diabetes health team about the result and whether any changes should be made.
The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 1993 Sep 30;329(14):977-86.
DiMeglio, LA et al. ISPAD Clinical Practice Consensus Guidelines 2018. Glycemic control targets and glucose monitoring for children, adolescents, and young adults with diabetes. Pediatric Diabetes October 2018: 19 (Suppl. 27): 105-114.
Diabetes Canada Clinical Practice Guidelines Expert Committee. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes. 2018;42(Suppl 1):S1-S325.
D. Wherrett et al. Canadian Diabetes Association 2013 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada: Type 1 Diabetes in Children and Adolescents. Can J Diabetes 2013;37(suppl 1):S154.
The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.
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