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10
| 3 | 2008
Klinisk Biokemi i Norden
ned values that are traceable to the reference method,
and can monitor the bias and imprecision of their key
methods by a special service from the IFCC network
coordinator (13).
The fraction of the amount of N terminally glyca-
ted beta chains to the total amount of beta chains is
a real
in vivo
variable independent of measurement
procedure. To distinguish this variable from “the old
HbA1c”, it has been agreed to express results in a unit
which differs from the traditional ‘% units’. The unit
‘mmol/mol’ was recommended by the IFCC/IUPAC
Committee on Nomenclature, Properties and Units
(C-PNU) (14). However, no agreement was achieved
to denote the HbA1c(IFCC) with a new name. It
should be noted that the systematic description of the
measurand given by NPU is not intended as a name
used for everyday speech. The NPU code for the
HbA1c (IFCC) is NPU27300.
The fact that three different old HbA1c:s and the
new HbA1c(IFCC) all are called ‘HbA1c’, and that
sometimes slightly different names are used as syno-
nyms for the same measurand, might be confusing
(15, 16).
The transition towards standardization through
the reference method
Already in 2004 the linear relations between measu-
rement values from the three DCM:s and values from
the new IFCC reference method were described (12).
These linear relations, called Master Equations, are
since then monitored biannually in the IFCC net-
work program. The relation between HbA1c(IFCC)
and HbA1c(NGSP) has remained unchanged since
the start of the comparisons 2001: “HbA1c(NGSP) =
0.092 x HbA1c(IFCC) + 2.15” (13). The results repre-
sent the mean of 9 laboratories in USA and Europe.
The relations between IFCC and JSD, and IFCC and
Mono S have changed slightly during the follow up
period. Since the biannual comparisons 2003, the
relation between IFCC and Mono S has been shown
to be very stable and described by the EQUALIS-
equation: “HbA1c (Mono S) = 0.96 x HbA1c(IFCC) +
1.02”. The reason for the small difference between the
very early relations and the later ones might be that
up to 2002 the whole EDTA blood was distributed to
the participants in cold pack and from 2003 as frozen
whole blood, which improved the quality of the mate-
rial for HPLC systems.
It should be noted that the Master Equations and
the EQUALIS Equation can be used to express a
HbA1c(NGSP) number or HbA1c(Mono S) number
from an IFCC traceable HbA1c value. The equation
are not intended to be used the other way, that is
to derive a HbA1c(IFCC) number from a NGSP or
Mono S traceable HbA1c value, because the traceabi-
lity chain is from the IFCC reference method as the
method of highest metrological hierarchy.
Corresponding numbers between NGSP, MonoS
and IFCC standardization are shown in table 1. A rule
of thumb might be that the incremental step in IFCC
scale is 11 mmol/mol for each % NGSP-unit.
InMay 2007 a consensusmeeting was held inMilan,
Italy. The clinical organizations American Diabetes
Association (ADA), the European Association for
the Study of Diabetes (EASD), and the International
Diabetes Federation agreed together with IFCC in
a consensus statement that “HbA1c results are to
be reported world-wide in IFCC units and derived
NGSP units, using the IFCC-NGSP master equation”
(17).
The world manufacturers of HbA1c devices have
therefore agreed to make all results traceable to the
IFCC reference measurement procedure. Deadline
for traceability to the IFCC reference method is
December 31
st
2009. For convenience of the end
users, and to avoid confusion, the results should be
reported both as IFCC figures with unit ‘mmol/mol’
and, after calculation with the Master Equation, as
NGSP figures with unit ‘%’ HbA1c. From January
1
st
2011 all new instruments must report both IFCC
values and NGSP values in parallel. Furthermore, for
the simplification of the interpretation of the HbA1c
result, the ADA and EASD have also asked for the
estimated mean blood glucose (eAG) to be reported
together with the two HbA1c values (18). If, and how,
the different figures should be handled by the end
users is not yet clear and are discussed with the diabe-
tes professions in different countries world-wide.
A special challenge for Sweden will be the transi-
tion fromMono S traceability to IFCC traceability. To
make future results traceable to IFCC, Mono S users
must calibrate the measurements with calibrators to
which FCC values are assigned. To express results in
Mono S numbers, the EQUALIS-equation “HbA1c
(Mono S) = 0.96 x HbA1c(IFCC) + 1.02” will be
used.
(Fortsat fra side 9)
(Fortsætter side 12)
