HI, have a look at the short link below:

http://www.mayomedicallaboratories.com/articles/hottopics/transcripts/2009/2009-7a-hba1c/7a-13.html

It shows some basics of the methods.

Some points about the case:

Be sure to determine that the patient does not have a rare hemoglobinopathy like HbD or other asymptomatic varieties, or even a slight case of G6PD deficiency or some hemolytic disease that doesn´t have a clinical appearance, though. To be sure, it might be useful to order an Iron cynetics panel, including a Direct Antiglobulin test, just to make sure. Also, try to have access to past Glucose determinations, or even do an experiment of about 3 - 6 months comparing both HBa1C result determination (say, every month or every 2 months) with monthly glucose determinations.

But then, boronate affinity and HPLC methods do measure different phenomena. They will be intecomparable on a population basis, provided you have sound methodlogy and validation of both methods, and it is OK to use any one of them. But there will always that one patient whose result would differ among both problems due to some individual determinants. This patient shold be considered an "outlier" and, perhaps,  better excluded from the statistical analysis.

If you´re willing to decide which method you´re going to adopt as routine, I suggest you don´t be deferred by that. Choose by any other determining factors like costs, reliability of the brand, technical support etc. the two methods should be equivalent to each other for the bulk of your patients, and either way some occasional patients' results might require further analysis. That´s what we Pathologists are, after all!... :-)

If you´re willing to study the particular patient - it might give some insight into your methods - I think that above suggestions  are a good start.

Please let me know if I ´ve been of any help.

In a study,  published in Medicinal Chemistry by Genc S, estimated

mean difference of the methods from CE were found very small; -0.25 %

(-0.67 - 0.17) for TINIA, -0.03 % (-0.42- 0.35) for boronate affinity and,

0.07 % (-0.26-0.40) for cation- exchange HPLC method.

http://dx.doi.org/10.4172/2161-0444.1000185

http://dx.doi.org/10.4172/2161-0444.1000185

Ion-exchange HPLC separates Hb species based on charge differences between HbA1c and other hemoglobins. Charge based separation methods show significant interference from Hb variants which alter the charge on the molecule. 

In boronate affinity methods, m-aminophenylboronic acid reacts specifically with the cis-diol groups of glucose bound to Hb. This method measures total glycated GHB, including HbA1c and Hb glycated at other sites, and tends to demonstrate the least interference from the presence of Hb variants and derivatives. 

Kindly find specific information about interference in Hb A1c estimation by variants in this link.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769887/table/tbl1/