Fasting glucose – is it still relevant when managing patients with T2D?

27th January 2019, Dr Chee L Khoo

It’s tempting to rely too much on HbA1c when managing our patients with type 2 diabetes (T2D). It is not uncommon to come across patients with pretty optimal HbA1c (under 6.5-7.0%) and we pat them on the back with the message “well done”. Often, the fasting glucose levels is just glossed over. Should we even bother with the fasting glucose levels at all these days?

A recent study looked at pooled data from 7 databases including Framingham, Framingham Offspring, ARIC, CARDIA, Cardiovascular Health Study, and Jackson Heart study. They looked at fasting glucose (FG) level and its correlation to future cardiovascular (CV) events. These studies spanned over 30 years and fasting glucose was used because not all the studies had HbA1C data. Data was available from 19,630 patients, some with diabetes, some without.

The results

In non-diabetics

In patients who did not have diabetes, CV event rates did not rise with increasing fasting glucose levels (up to 6.2 mmol/L) in both men (~23%) and women (~16%).

In patients with diabetes

However, in patients with diabetes with fasting glucose >7.0 mmol/L, CVD event rate rose to 47.4% in men and 38.6% in women.

CV event rates according to glucose tolerance

The authors also looked at the CV event rate from a different angle. Using 20 year data, they used fasting glucose to categorise patients into either normal, prediabetes or diabetes. For women, the normal group had 4.1% CVD events, which was almost identical to the prediabetes women who had 4.2% CVD events. But the women with diabetes had 25.8% CV events. For men, they saw the same pattern. Normal and prediabetes patients were similar at 8.1% and 10.7%, but the men with diabetes had 31.6% CVD events.

Thus, there appears to be a fasting glucose threshold level beyond which it becomes a problem. The results of this study actually, isn’t that surprising. When one assess glycaemic control in patients with T2D, it has always been taught that we need to look at a triad of readings – fasting, post-prandial and HbA1c.

Every time your blood glucose goes above 7 mmol/L, some damage occurs. If you don’t have diabetes, you still have capacity to keep your post prandial glucose under control and limit any damage. But once diabetes is diagnosed, post prandial glucose control is compromised. Post prandial glucose is often in the hyperglycaemic range and CV events rate then increases.

Access the abstract here

Reference:

Michael P. Bancks, Hongyan Ning, Norrina B. Allen, Alain G. Bertoni, Mercedes R. Carnethon, Adolfo Correa, Justin B. Echouffo Tcheugui, Leslie A. Lange, Donald M. Lloyd-Jones and John T. Wilkins. Long-Term Absolute Risk for Cardiovascular Disease Stratified by Fasting Glucose Level. Diabetes Care 2019 Jan; dc181773. https://doi.org/10.2337/dc18-1773