In an earlier blog I pointed out some of the reasons that people using insulin can have rollercoaster blood glucose levels from time to time, is it these variations that lead to complications?
I got interested in this after seeing a study in this month’s Diabetes care which investigated the association of A1C levels and fasting plasma glucose (FPG) with diabetic retinopathy and how well the two measures discriminated between people with and without retinopathy. Out of the 1,066 individuals, 11% them had retinopathy. (Retinopathy was defined as level 14 or above on the Early Treatment Diabetic Retinopathy Study severity scale. Level 14 equates with mild non proliferative retinopathy.) They found that HbA1c was the better discriminator and that the steepest increase in retinopathy prevalence occurred in people with a relatively low A1C of ≥5.5%.
At first sight it seems quite shocking, retinopathy with a Hb A1 of 5.5%, that’s well within my laboratories normal range . On reflection, it shouldn’t really cause any surprise as the DCCT (Diabetes Control and Complications Trial) showed a small number of subjects with complications at this level. The probability of it progressing is small, but that ‘chance’ still exists.
A small number, but it represents real people who wonder why it had to happen to them.
It happened to me, I was horrified to be told that I had some mild background retinopathy. I had been diagnosed for 4 years, I had checks every year for 3 years with nothing found. Then, before going on the pump. I had to have an extra check using fluorescein dye. This was a compulsory part of the procedure in France, and is because many people going onto pumps have quite high glucose levels. The change to pumping can lower levels rapidly and this can cause rapid progression of retinopathy. The angiogram, would show if care was necessary in reducing levels. My 'problem' wasn't high levels though but hypos and an active lifestyle. Both my doctor and I thought that it would be a formality. Fortunately, the changes were slight, but they were clearly there.
In her blog,* Jenny Ruhl discusses some theories why a person with a lowish HbA1c might develop retinopathy. She points out that an HbA1c can be the result of very different day to day patterns of glucose levels.
Two patterns that would result in the same Hb A1c, one clusters around the mean, the other has far larger glycemic excursions
She suggests that the ‘normal people’ in the study who had early retinopathy might have higher postprandial levels (fuelled by a high carbohydrate diet) followed by lower levels, such people could be be experiencing ‘oscillations that veered between 75 and 150’.( 4.2 and 8.3).
In contrast she suggests that people who control their diabetes well might different patterns. She describes a ‘ pattern in which the blood sugar stays near 112 (6.2mmol) all day long,' or alternatively , one with a relatively high fasting glucose of about 110 (6.1mmo) ,very narrow fluctuations at meal time, perhaps up to 120(6.6mmol) and then back down to 90(5mmol) . This she suggests is a pattern achieved by reduced carbohydrates plus necessary oral medication or insulin..
She implies that day to day and within day glucose variability as characterised by the first pattern might help to explain the incidence of retinopathy at relatively low HbA1c levels . In other words the ups and downs are important.
Jenny Ruhl advice is to’ keep track of your post-meal highs and keep them under 140 mg/dl as much as possible’ and this is surely the safest course and what most of us try to do. By doing this the overall average blood glucose level and presumably the Hb A1c is kept down. Yet increasingly some doctors and diabetes authorities are saying that those people who don’t need to adjust insulin doses should be concerned with the overall HBA1c and not the day to day variation. Moreover, there are many people, particularly type 1s who find it very difficult to limit their glucose excursions to a narrow band, too low post prandial levels, too low levels before exercise or before bed can result in serious hypos, a much more immediate complication. Thinking about this lead to some big questions
· Is day to day and within day glucose variability more significant or as significant as HbA1c in the development of complications?
· Is it the same answer for both micro and macro vascular complications?
· Is there a difference between type 1 and 2 (LADA, MODY???)
Back to my personal interest.
When background retinopathy was discovered my HbA1c taken a week before was 4.9% Since diagnosis it had been in the low 5s. I rarely had recorded glucose levels over 140, I had a fair number of hypos, almost always during exercise and very quickly remedied. At the time I was going to bed at about 80mg/dl...so for at least 10 hours of the day my level was ‘normal’ .
Now it is possible that the retinopathy was there before diagnosis and only became visible with the more detailed examination. Was I simply unlucky, or did the blood glucose excursions to below 70mg/dl and back up to normal levels play a part?
I’ve been trying to find the answers to those questions.
Like everything, it seems to depend on who you ask! (Or rather what you read)
To be continued...........!
* http://diabetesupdate.blogspot.com/2009/10/does-55-a1c-predict-retinopathy.html
Very interesting, will look forward to reading your findings! I also have a low HbA1c (5.6%) and have been told I have background retinopathy. But like you, I would find it extremely difficult doing my running if around 6 mmol/l 2 hours post-prandial.
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