Average glucose, HbA1c and spikes.

(sorry about the length I've spent ages trying to cut it down :!: )
Do Hb A1c and average blood glucose represent different things ?
Do people with similar averages have similar HbA1cs?
Is it really more dangerous to have blood glucose levels that go up and down over the day than the same average with fewer variations?

There are many opinions* but little evidence. One researcher, Eric Kilpatrick has looked at the available data from the DCCT( a 10 year type 1 study with a further 10 year follow up)
Every quarter during the DCCT and EDIC the subjects had 7 blood tests over a single day recorded .Kilpatrick has analysed these records.
Here are some of his findings from this data.
Which test is the best predictor of
microvascular risk in type 1 diabetes?
HbA1c
Mean blood glucose
Equally predictive

Does increasing glucose variability
lead to:
• A large increase in retinopathy risk?
• A small increase in retinopathy risk?
• No increase in retinopathy risk

Which test is the best predictor of
cardiovascular risk in type 1 diabetes?
HBa1c
Mean blood glucose
Equally predicitive
Taken from a powerpoint presentation which is well worth looking at with a lot about the risks at various levels.
http://www.york.ac.uk/healthsciences/diabetes/2008conf/ekilpatrick.pdf

His paper on CVD briefly discusses as to why average bg is different to HBA1c and why mean blood glucose might be a better predictor of macrovascular and HbA1c of microvascular disease.
(my underlining)

From a clinical perspective, this study reaffirms the usefulness of pre- and post-meal blood glucose measurement as an adjunct to HbA1c, especially in patients whose MBG is not entirely concordant with their HbA1c value. In this regard, an independent analysis of the DCCT dataset showed that individual patients with an MBG of, say, 10 mmol/l can have mean HbA1c values between 6 and 10% [13]. The reasons for these differences are multifactorial but are likely to include between-individual variability in erythrocyte survival, differences in the rate at which participants glycate their haemoglobin at the same glucose concentration [25] and variability in the relationship between mean glucose and HbA1c, depending on the glycaemic control of the population being studied [26]. Nonetheless, why MBG should be a better predictor than HbA1c of time to first cardiovascular event in the DCCT remains uncertain. It is, however, just possible that markers of hyperglycation (such as HbA1c) are superior at predicting the microvascular complications of diabetes, while hyperglycaemia is better for assessing cardiovascular risk

Click to expand...

http://www.springerlink.com/content/u03 ... ltext.html

Probably the only research that would give better data is a long term project using continuous monitoring and that would be very expensive.
* For an alternative argument on the risk of variable intraday glucose levels.( a debate between Kilpatrick and Monnier who thinks that variability is important in type 2)
See the second part of this paper 'Glucose variability'
http://www.diabetes.procampus.net/cours ... _Nov07.pdf