This is an old thread in 2003 that I found in my yahoo mail archive, it reminded me of the lively debate we used to have on this forum and how we predicted that HbA1c could be used as a diagnostic test long before the WHO consultation document in 2011:
Mohammad
Dear Eric
>
> This assumption can be true for every analyte for e.g if a patient has a serum creatinine of 50 umol/L that doubled (renal clearance halved) to 100 umol/L but it is still within the ref. range. This has never stopped us from using serum creatinine to assess renal function. Ofcourse, it would be far better if we know the individual's baseline anlyte concentarions before disease starts to quantify the changes that are significant, but this is currently impossible.
>
> My argument is limited to using fasting glucose and HbA1c in defining glycaemic status of individuals with previous normal/impaired fasting glucose instead of performing a GTT on them. I have double checked the HbA1c on the three cases which came as 7.4%, 6.2% and 5.3% respectively, such is the excellent between assay precision of the Tosoh analyser. It is traditional to do 3 jabs per GTT at our hospital.
>
> Apart from these 3 cases, I have been doing HbA1c on a lot of impaired fasting glucose samples and a strong positive correlation is observed in most of them. The DCCT cut off levels of HbA1c for categorising glycaemic contol, do not take into consideration the initial HbA1c of individual patients before the diabetic process has started, but this is true for other analytes as I stated.
>
> regards
>
> Mohammad
>
> Dr. M Al-Jubouri, Consultant Chemical Pathologist
>
> >From: Eric Kilpatrick
> >Reply-To: Eric Kilpatrick
> >To: [log in to unmask]
> >Subject: Re: HbA1c more honest than GTT
> >Date: Thu, 24 Apr 2003 14:16:50 +0100
> >
> >A year ago I gave a reply to the same question by Paul Masters. I still think it holds true:
> >
> >Paul
> >
> >It is unlikely that HbA1c will ever be a reliable test for the diagnosis of
> >type 2 diabetes for the following reason. If hyperglycaemia, rather than
> >glycation, is the true cause of diabetic complications (and it continues to
> >be the means of diagnosing diabetes) then HbA1c is fundamentally limited by
> >the fact that 2 individuals with the same degree of glucose tolerance can
> >have HbA1c values which differ by nearly 2% (ref interval 4-6%).
> >Thus, a subject with a HbA1c of 4% would need to abnormally increase his/her
> >glycation rate by 50% to match another non-diabetic subject with a HbA1c of
> >6%. It is therefore not surprising that there can be overlap between the
> >HbA1c values of diabetic patients with those of non-diabetic subjects. Even
> >if glycation is thought to be the underlying reason for complications, we
> >have to be sure that glycation of haemoglobin gives an accurate reflection
> >of glycation in small vessels. Since it is known that HbA1c values can be
> >affected by factors which are independent of glycaemia or glycation rates
> >(such as inter-individual variations in red cell survival) then this
> >assumption cannot be presumed.
> >
> >You can tell this is a hobby horse of mine, but it is bad enough persuading
> >GPs not to test HbA1c for diagnosis without a case of 'et tu Brute'!!!
> >
> >Eric
> >
> >PS Mohammad's Case 1 still looks a bit suspicious though
> >PPS Why are the patients being jabbed 3 times rather than twice?
> > ----- Original Message -----
> > From: Mohammad Al-Jubouri
> > To: [log in to unmask]
> > Sent: Thursday, April 24, 2003 10:10 AM
> > Subject: HbA1c more honest than GTT
> >
> >
> > I present to you 3 GTTs with corresponding HbA1c performed on fasting samples from yesterday work in our lab in support of above statement:
> >
> > 0h 1h 2h HbA1c GTT interpret.
> >
> > 1. 55 year old man 6.8 14.1 10.5 7.5% IGT
> >
> > 2. 60 year old man 6.3 14.1 12.5 6.2% DM
> >
> > 3. 62 year old man 5.1 11.8 12.8 5.4% DM
> >
> > Do you think that HbA1c should be given a leading role in diagnosis of IGT/DM and forget about artificial GTTs? A question for WHO experts.
> >
> > Mohammad
> >
> >
> > Dr. M Al-Jubouri, Consultant Chemical Pathologist
> >
> >
> >
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