Sample stability for the measurement of hemoglobin A1c
Letter to the editor
Sample stability for the measurement of hemoglobin A1c
According to the American Diabetes Association (ADA),the measurement of hemoglobin A1c (HbA1c)can be used for diagnosing diabetes and it should also be performed routinely in all patients with diabetes at initial assessment and then as part of continuing care [1].Little is known,however on preanalytical variables in?uencing test results [2].In particu-lar,the storage of samples might be necessary for a variety of reasons,including delayed transfer of the specimens from peripheral collection centers and/or clinics to the core laboratory where the measurement is performed,instrument malfunction,re-testing and clinical retrospective studies.
Twenty-seven consecutive whole blood samples collected in K2EDTA referred from the outpatient phlebotomy center for routine HbA1c testing were divided in three different aliquots.For the optimum sample type studies,the specimens were immediately processed (fresh sample)or stored at either +48C or à808C for 1week and assayed afterward.HbA1c was measured in duplicate by high pressure liquid chromatogra-phy (HPLC)using VARIANT II HbA2/HbA1c Dual Program (Bio-Rad Laboratories S.r.l.,Milano,Italy).
The HbA1c results were homogeneously distributed within a broad measuring range,including either normal or pathological values (Fig.1).An overall excellent correlation was observed between fresh and specimens stored at either +48C or à808C (both r =0.999;p <0.001).The coef?cient of variation (CV%)was 0.80%(95%CI:0.51–1.08%)for samples stored +48C,and 0.70%(95%CI:0.48–0.92%)for those stored at à808C (Fig.1).The mean bias from the reference fresh specimens was slightly lower in samples stored at à808C (0.04%;95%CI from à0.12to 0.21%)than in those stored at +48C (0.09%;95%CI from à0.15to 0.32%).In no case however the bias exceeded the 1.5%desirable analytical quality speci?cations for HbA1c [3].
In an earlier investigation,Selvin et al.showed that highly correlated but more variable and slightly higher HbA1c results were obtained from frozen whole blood samples that have been in storage at à708C for over a decade [4].The large biases observed have been attributed to the two different analyzers (Tosoh A1c 2.2Plus HPLC before storage and Diamat Bio-Rad after storage)that were used for measurement.Ezenwaka et al.also compared fresh whole blood samples with pre-determined HbA1c values before and after 20days of storage between 2and
88C.Their results showed no signi?cant differences in the mean values of the initial HbA1c measurement and the values obtained after storage.Signi?cant correlation was also observed between the HbA1c values measured in fresh whole blood samples and values obtained after storage (r =0.83;p <0.01)[5].In conclusion,results of our investigation demonstrate that whole blood specimens for HbA1c testing can be suitably stored at either +48C or à808C for up to 1week and reliably assayed afterwards since no clinically meaningful bias was introduced by either storage condition.
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Fig.1–Bland–Altman plots for the independent
measurements of hemoglobin HbA1c in whole blood specimens stored at either +48C or S 808C for 1week as compared with the reference fresh sample.Horizontal lines are drawn at the mean percent difference
(continuous),and at the mean percent difference plus and minus 1.96times the standard deviation (SD)of the percent differences (dotted).
C o n t e n t s l i s t s a v a i l a b l e a t S c i e n c e
D i r e c t
Diabetes Research and Clinical Practice
journal homepage:https://www.sodocs.net/doc/0717784576.html,/locate/diabres
Con?ict of interest
The authors declare that they have no con?ict of interest.
r e f e r e n c e s
[1]American Diabetes Association.Diagnosis and classi?cation
of diabetes mellitus.Diabetes Care2010;33:S62–9.
[2]Weykamp C,John WG,Mosca A,Hoshino T,Little R,
Jeppsson JO,et al.The IFCC reference measurement system for HbA1c:a6-year progress report.Clin Chem2008;54:
240–8.
[3]Ricos C,Alvarez V,Cava F,Garcia-Lario JV,Hernandez A,
Jimenez CV,et al.Current databases on biologic variation:
pros,cons and progress.Scand J Clin Lab Invest1999;59:
491–500.
[4]Selvin E,Coresh J,Jordahl J,Boland L,Steffes MW.Stability of
haemoglobin A1c(HbA1c)measurements from frozen whole blood samples stored for over a decade.Diabet Med
2005;22:1726–30.
[5]Ezenwaka CE,Seales D,Surujlal R,Mathura RP.Glycated
haemoglobin A1c measurement in stored whole blood
sample is reliable for clinical use.West Indian Med J
2009;58:17–20.
Mariella Mercadanti
Alberta Calef?
U.O.di Diagnostica Ematochimica, Dipartimento di Patologia e Medicina di Laboratorio,
Azienda Ospedaliero-Universitaria di Parma,
Parma,Italy
Giovanni Targher
Sezione di Endocrinologia, Dipartimento di Scienze Biomediche e Chirurgiche,
Universita`di Verona,
Verona,Italy
Giuseppe Lippi*
U.O.di Diagnostica Ematochimica, Dipartimento di Patologia e Medicina di Laboratorio,
Azienda Ospedaliero-Universitaria di Parma,
Parma,Italy
*Corresponding author at:U.O.Diagnostica Ematochimica, Azienda Ospedaliero-Universitaria di Parma,
Strada Abbeveratoia2/a,43100-Parma,
Italy.
Tel.:+390521703050/703054;fax:+390458027484
E-mail addresses:glippi@ao.pr.it
giuseppe.lippi@univr.it
ulippi@tin.it(G.Lippi)
13May2010
Published on line17June2010
0168-8227/$–see front matter #2010Elsevier Ireland Ltd.All rights reserved.
doi:10.1016/j.diabres.2010.05.014
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