300 versus 180

I have often wondered which is worse, or does it matter?

High bloodsugars are not good, but is it worse to have a 300 versus a 180?

Is having a 300 harder on our bodies, or is it the length of time it takes to get it back into normal range?

I really don’t know for sure - but I suspect the length of time would have a lot to do with it. Our bodies in general can handle all sorts of things but there has to be a cut off limit. In saying that, a 300 surely has to be worse than a 180? That’s thicker gluggier blood and harder for the body to use.

Mentally I know a 300 is much worse than a 180, for the stress and guilt it causes, and that alone can make it so much worse!

I think a BG in excess of 180 is when the kidneys start leaking sugar into the urine. Besides, the viscosity of blood also increases as your BG goes up. So 180 vs 300 does make a difference.

Yes, 300 is worse than 180. The body has a sort of “dose-response” relationship with blood sugar – that is, the higher it goes, the harder it is. Sort of like a poison: a little might not kill you but if you take enough you’ll do some harm.

The length of time is also important however. Being at 300 for a few minutes is “probably” less worse than being at 180 for days at a time. I don’t know if there is any research that specifically notes this, this is the most logical conclusion given the physiology.

I forgot to mention that the current gold-standard is the HbA1C, which is an average of all your blood sugars of the last two or so months. So, having a BG of 300 versus 180 would make your HbA1C higher, and the more frequently your sugar is elevated, the higher your A1C.

The big problem with highs seems to be that nerve and eye cells do not require insulin to take in glucose. The more in the blood that reaches them, the more they take in. Once in the cell the glucose does bad things and changes the cell.

It’s kind of like if you dip a piece of bread in soup. The saltier the soup, the saltier your bread will be because it will absorb more.

Now if your blood sugar drops very quickly, as happens to Type 1s, the glucose will get pulled out of the cell since I’m pretty sure it flows to where the concentration is lower. That is why keeping spikes as brief as possible is recommended. But some of it may stick.

That is why doctors often look at the A1c, which despite what you are told is NOT an average. It’s a measure of how many blood cells have glucose permanently stuck to them. Glucose sticks to blood cells permanently after some time (12-24 hours. I don’t recall exactly). Before that time the sticking process is reversible. So the amount of glucose stuck to your blood hints at the amount of glucose stuck inside your nerves or eye cells.

Jenny, while you are correct that the A1C is not an average per se, it can be interpreted as an indicator of the trend of the average blood glucose, to very close approximation. There are formulas that can be applied to convert a given value of HbA1C to approximate average BG levels.

The science is this: blood glucose binds to the A1C subgroup of hemoglobin, and it also decomposes but at slower rate. The amount of glucose that is bound then reaches a steady state that is slight skewed towards the previous 4 weeks or so. The amount of glucose that is bound gives a relatively good indication of the average blood glucose. It is important to note that the blood cells only live in the body for 3-4 months themselves and are constantly being recycled. So in any blood sample, there will be a mix of new and old blood cells that will varying levels of glucose bound to the A1C subgroup.


I know all about what the Science is. But hundreds of people have posted online who test their blood sugar intensively and find their A1c doesn’t come near the supposed averages. I’m one. One friend went so far as to use a CGMS for a month because her meter average was so different from the A1c. The meter readings turned out to be right.

The problems show up with those of us who maintain normal and near normal blood sugars. The A1c formulas derived from the DCCT and appear to work (if they do work) for a population with an average bg of 180 or higher. If your true average is under 110, the DCCT formulas will give a much higher than true equivalent.

Furthermore, it turns out that the lower your blood sugar, the longer your red blood cells live, which paradoxically raises how much glucose they collect.

I have written this up on my blog at: http://diabetesupdate.blogspot.com/2006/12/formulas-equating-hba1c-to-average.html

The data about length of life of red blood cells is in from a study linked below. They measured the lifetimes of hemoglobin cells in normal people and diabetics and found that the cells of the diabetics turned over much faster–as little as 81 days, while normal people’s could live up to 146 days.

They suggest that getting better control will cause the cells to live longer (and continue to glycate as they do) which could explain a slight increases in A1c in people making significant improvements in blood sugar at levels closer to normal control.

This data also suggests if you have good control and get much better control, you probably want to test only every 6 months, not every three.


That was really helpful, Jenny. Thanks!

"The problems show up with those of us who maintain normal and near normal blood sugars. The A1c formulas derived from the DCCT and appear to work (if they do work) for a population with an average bg of 180 or higher. If your true average is under 110, the DCCT formulas will give a much higher than true equivalent."

The study you cite actually says the opposite of this, sort of. The authors note that the higher the blood sugar, the less accurate the A1C. In individuals with very high blood sugar they show that the A1C underestimates the actual BG up to 50%. In normoglycemic individuals the test should actually be more accurate, according to this study.

I would also question the accuracy of blood glucose meters or CGMS as the standard with which to compare your A1c. As I noted in another discussion this weekend, my two meters are often as far apart as 15-20 mg/dl which can be a major difference in A1c using the formulas (5.5 vs. 4.9 with 120 and 100 respectively).

The A1c is clearly a flawed test and there needs to be a better way to represent BG control. However, the A1c is still useful as a measure of overall control but should not be used as the ONLY measure of control.

I feel like I may be pulling this discussion off topic a little bit. This is certainly an interesting discussion and I would be very happy to talk about these tests more in a different thread, if you’d like. Thanks for the interesting links as well!


The point of using a CGMS to check out the A1c is when the doc says, “Oh, you must be going very high at night, or you missed the spike after the meals with your meter test.”

Then you use the CGMS and there IS no spike. So the explanation for that A1c isn’t that you missed the spike. My friend low carbs very stringently, and her “spikes” e weren’t over 130 mg/dl, Ever. So how the heck did she end up with a 6.6%?

I think it wouldn’t be such an issue with me if the doctors weren’t so utterly convinced that the A1c really measured the average. To the point where none of my doctors ever looks at my blood sugar logs.

Jenny, I totally agree. A thorough practitioner should never look at one lab result as the basis for changing a care strategy. I have had amazing luck with my endo who routinely checks my logs, in addition to my A1c and fructosamine (which shows more recent excursion since I have very tight control) before modifying any of my treatment plans.

What a lot of good information here - the depth of knowledge you guys have is wonderful.