Appendix C. Glycohemoglobin (GHb) Testing

GHb (glycated hemoglobin, HbA1c, HbA1) describes a series of stable minor hemoglobin components formed slowly and nonenzymatically from hemoglobin and glucose. This alteration in HbA is a post-translational modification [4644].

Rahbar et al. demonstrated elevation in the minor HbA fractions in patients with diabetes using gel electrophoresis (Rahbar, et al. 1969; [92177]; Rahbar, et al. 1986 [92178]).

Historical perspective:

HbA1 can be separated into three minor components that have a more negative charge:

1. HbA1a
2. HbA1b
3. HbA1c

HbA1c was the component resulting from post-translational modification of HbA by glucose at the N-terminus of the β chain. HbA1c has been correlated with:

1. fasting plasma glucose
2. glucose peak during glucose tolerance test
3. area under the curve of glucose tolerance test
4. mean glucose levels over preceding few weeks

[4644].

Glycohemoglobin nomenclature:

Table

Glycated hemoglobin measurement methods available in US as of 2002

Table

College of American Pathologists (CAP) Survey Data (updated 5/02)

The American Diabetes Association (ADA) recommends that laboratories use only GHB assay methods that have been NGSP certified and report results as “%HbA1c” or “%HbA1c equivalents”. The ADA also recommends that all laboratories performing GHB testing participate in the College of American Pathologists (CAP) fresh sample proficiency testing survey (see ADA Recommendations section on this website for more details). The following methods were included in the recent 2002 CAP GH2 survey:

Methods reporting HbA1c or equivalent:

Bayer DCA 2000

Beckman Synchron Syst

Bio-Rad Diastat

Bio-Rad Variant A1c

Bio-Rad Variant II A1c

Dade Behring Dimension

Primus (affinity)

Roche Cobas Integra

Roche/Hitachi (Tina Quant II)

Tosoh A1c 2.2 Plus

Tosoh G7 Auto HPLC

Abbott IMX

Beckman Diatrac

Methods reporting total GHb:

Abbott IMX

Bio-Rad Variant

Helena Glyco-Tek

Primus

Adapted from NGSP Website (www.ngsp.org).