يسم الله

Just when I thought life was simple, I am starting to understand that HbA1c is not quite what it is meant to be.

First of all it is a dying breed and will be replaced by a new number which is no longer a percentage (Ref):

HbA1c-DCCT                              HbA1c-IFCC
(%)                                                (mmol/mol)
4.0 20
5.0 31
6.0 42
7.0 53
8.0 64
9.0 75
10.0 86

And why are they doing this?

Because now we are using a more accurate measure of glycosylation of Hb by looking at a single Valine on of the Hb chains rather than using a biological assay which included glycosylation of other things as well as Hb (but UKPDS used this ‘biological’ test! – So is validity true?)

And then I started spotting HbA1c and FG & 2HPP discrepancies:

So I needed to add a bit more to my HbA1c rudimentary knowledge: turns out the 120 day is not quite an accurate picture. The previous 30 days has a 50% impact on the HbA1c while the days 90-120 (before the test) only have a 10-20% effect on it. (http://www.endocrinetoday.com/view.aspx?rid=61106) . So the fresher your RBCs are and the worse your recent sugars are the higher your HbA1c will be even though the MPG (Mean Plasma Glucose) may be unchanged. (MPGs can be worked out by 7 measurements per day – super snazzy glucose meters that sample your glucose automatically).

So does the average life cycle of a red blood cell differ by ethnicity / genetic profile? From the anecdotal lack of complications in my diabetics with HbA1cs off the Richter scale (10-15%) the answer sees to be yes – at least in Saudi Arabia.

Does BTS (Beta Thallasemia Trait) have an effect?  Potentially depending on the assay it seems is a possibility. (Ref)

Vitamin B12: Yes – no – yes again? Should we be checking Vitamin B12 once a year? Read this case report which argues for a yes: Report of Metformin induced B12 deficiency and neuropathy.

And then finally to cap it all off – statins can increase your risk of diabetes by 9%! This is the result of a meta-analysis published in the Lancet in Feb 2010. (Read more here). In short if you are low risk then it may not be a good idea, for moderate to high risk and if your old it works out as follows:

Results further revealed that treatment of 255 patients with statins for four years would result in one extra case of diabetes. But, for 1 mmol/L reduction in LDL concentration, the same 255 patients could expect to experience five fewer major coronary events, such as coronary heart disease death or nonfatal myocardial infarction.

Hope you are good at statistics and risk analysis and perhaps a bit of Bayes theorem.

//

Tayside Diabetes Handbook – Change in Reporting of HbA1c

What is HbA1c?
Glucose in the blood binds irreversibly to a specific part of haemoglobin in red blood cells, forming HbA1c. The higher the glucose, the higher the HbA1c. HbA1c circulates for the lifespan of the red blood cell, so reflects the prevailing blood glucose levels over the preceding 2-3 months
What does it tell us?
The DCCT in Type 1 diabetes and the UKPDS in Type 2 diabetes both showed that the risk of microvascular and macrovascular complications of diabetes increases as HbA1c increases. HbA1c thus gives a measure of an individual’s risk of the long-term complications of diabetes.
Why measure it?
HbA1c measured 3-6 monthly shows how an individual’s glucose control, and thus risk of complications, changes in response to alterations in management. Target HbA1c levels can be set for individual patients and therapy adjusted to reach them.
Current HbA1c Numbers
Current HbA1c assays are aligned to the assay used in the DCCT, so that an individual’s risk of complications can be inferred from the result. The non-diabetic reference range is HbA1c-DCCT 4.0- 6.0 %
Current Targets
The general target currently is HbA1c-DCCT <7.0 %. However, this should be individualised, considering the person’s risk of severe hypoglycaemia, cardiovascular status and co-morbidities.
Why Change?
The new IFCC reference method is more specific for HbA1c than the assay used for standardisation in the DCCT and UKPDS. Comparing results from different labs throughout the world and interpreting clinical trial results will now be easier. In future, HbA1c-IFCC results will be reported in mmol/mol after standardisation using the IFCC reference method
New Units and Numbers
The non-diabetic reference range for HbA1c-IFCC using the IFCC reference method will be 20- 42 mmol/mol, rather than the HbA1c-DCCT-aligned range of 4.0 – 6.0 %.
How Old and New Relate
A guide to the new values expressed as mmol/mol is:
HbA1c-DCCT                              HbA1c-IFCC
(%)                                                (mmol/mol)
4.0 20
5.0 31
6.0 42
7.0 53
8.0 64
9.0 75
10.0 86
Advertisements

One thought on “HbA1c and all that!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s