SA JOURNAL OF DIABETES & VASCULAR DISEASE
REVIEW
VOLUME 7 NUMBER 3 • SEPTEMBER 2010
101
of pre-diabetes, they do recommend that prevention strategies are
considered in people at highest risk of developing diabetes and its
complications with an HbA
1c
between 6 and 6.5%, or an HbA
1c
below 6% in the presence of other diabetes risk factors such as
high blood pressure, elevated levels of triglycerides, increased body
mass index (BMI) and family history of diabetes.
6
It is important to note that HbA
1c
is not infallible, and results
may be unreliable in acute elevations of blood glucose and certain
haematological situations, particularly where haemoglobin or red
blood cell turnover is abnormal. HbA
1c
also increases with age. The
expert committee therefore highlights the fact that the superiority
of HbA
1c
testing does not invalidate FPG or the OGTT, which remain
acceptable alternatives when required, and it recommends that
whatever method is used, diagnosis should always be confirmed
with a repeat test. Investigation of diabetes during pregnancy will
continue to require glucose measurement.
6
HbA
1c
standardisation in the UK is changing
To achieve uniform international standardisation and allow global
comparisons, the way HbA
1c
measurements are expressed in the
UK is changing from a percentage to mmol/mol. HbA
1c
assays have
traditionally been aligned to those used in the DCCT, where HbA
1c
is
expressed as a percentage of the total haemoglobin concentration.
To ease the transition, both units can be used until June
2011, but after that date HbA
1c
values will only be expressed as
the International Federation of Clinical Chemistry and Laboratory
Medicine’s (IFCC) reference method of mmol/mol of haemoglobin
without glucose attached.
7
This changes means that the current HbA
1c
targets of 6.5% and
7.5% equate to 48 mmol/mol and 59 mmol/mol, and the non-
diabetic reference range of 4.0% to 6.0% equates to 20 mmol/
mol to 42 mmol/mol (see Table 2).
7
To help facilitate the change,
Diabetes UK has produced an easy-to-use online HbA
1c
converter,
which is available at
Information_resources/Changes-to-HbA
1c
-values/.
While the International Expert Committee’s recommendation on
the use of HbA
1c
for the diagnosis of diabetes has not yet been
adopted by current guidelines, it represents best current evidence
and so is a step in the right direction. Although patient education
will always play a large part in improving the early diagnosis of type
2 diabetes, using a simpler and more convenient tests such as HbA
1c
will undoubtedly help, and better standardisation of HbA
1c
in the
UK and globally will facilitate it further.
References
1.
Diabetes UK. Reports and statistics.
Diabetes Prev
2008. Available at:
.
diabetes.org.uk/Professionals/Publications-reports-and-resources/Reports-statis-
tics-and-case-studies/Reports/Diabetes-prevalence-2008/ (Accessed 22/08/09).
2.
Yorkshire and Humber Observatory (YHPHO)
Key Facts on Diabetes
. March 2006.
Available at:
<
yhpho.org.uk/resource/item.aspx?RID=8872> (Accessed 22/08/09).
3.
Williams R, Gillams S, Murphy M
et al
.(2002) In: Yorkshire and Humber Observa-
tory (YHPHO)
Key Facts on Diabetes
. March 2006. Available at:
.
org.uk/resource/item.aspx?RID=8872
.
aspx?RID=8872> (Accessed 22/08/09).
4.
Fowler M. Microvascular and Macrovascular Complications of Diabetes.
Clin
Diabetes
2008;
26
: 77–82. doi:10.2337/diaclin.26.2.77
5.
Alexander WD. In: Yorkshire and Humber Observatory (YHPHO)
Key Facts
on Diabetes
. March 2006. Available at:
aspx?RID=8872
<
>
(Accessed 22/08/09).
6.
The International Expert Committee. International Expert Committee Report on
the role of the A
1c
Assay in the Diagnosis of Diabetes.
Diabetes Care
2009;
32
(7):
1327–1334.
7.
Diabetes UK.
HbA
1c
Standardisation for Clinical Health Care Professionals
.
Available at
/
53130HbA
1c
HCPleaflet.pdf (Accessed 26/06/09).
8.
DCCT Research Group. The association between glycaemic exposure and long-
term diabetes complications in the Diabetes Control and Complications Trial.
Diabetes
1995;
44
: 968–83. doi:10.2337/diabetes.44.8.968.
9.
Stratton IM, Adler AI, Neil HA,
et al
. Association of glycaemia with macrovascular
and microvascular complications of type 2 diabetes: prospective observational
study (UKPDS 35)
Br Med J
2000;
321
: 405–12.
10. Tapp RJ, Tikellis G, Wong TY,
et al
. Longitudinal association og glucose metabolism
with retinopathy.
Diabetes Care
2008;
31
: 1349–54.
11. Sabanayagam C, Liew G, Tapp RJ,
et al
. Relationship between glycated
haemoglobin and microvascular complications: is there a natural cut-off point
for the diagnosis of diabetes.
Diabetologia
2009;
52
(7): 1279–89. doi:10.1007/
s00125-009-1360-5.
12. van Leiden HA, Dekker JM, Moll AC. Risk factors for incident retinopathy in a
diabetic and nondiabetic population: the Hoorn study.
Opthalmology
2003;
121
:
245–51.
13. Wong TY, Liew G, Tai ES,
et al
. Relation between fasting glucose and retinopathy
for diagnosis of diabetes: three population based cross-sectional studies.
Lancet
2008;
371
: 736–43. doi:10.1016/S0140-6736(08)60343-8.
Table 2.
Relationship between old and new HbA1C values
DCCT-aligned HbA
1C
(%)
IFFC-aligned HbA
1C
(mmol/mol)
6.0
42
6.5
48
7.0
53
7.5
59
8.0
64
9.0
75
(Adapted from
Diabetes UK
. HbA
1C
Standardisation for Clinical Health Care
Professionals
7
)
