HbA1c: a comparison of NGSP with IFCC transformed values

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Diabetes Mellitus Diagnostics

Background:

• An International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method for Hemoglobin A1c (HbA1c) is now available.
• This method correlates well with National Glycohemoglobin Standardization Program (NGSP) values.
• The study aimed to assess agreement between NGSP-certified and IFCC-calibrated methods for HbA1c measurement.

Purpose of the Study:

• To determine the agreement between NGSP-certified and IFCC-calibrated immunochemical methods for HbA1c.
• To evaluate differences in diabetes mellitus (DM) control classification for individual patients using both methods.

Main Methods:

• HbA1c was measured on 92 patient hemolysates using both NGSP and IFCC methods.
• Analysis included kappa statistic, linear regression, and McNemar's chi(2) test.
• The IFCC results were converted to NGSP values for comparison.

Main Results:

• Both methods demonstrated acceptable analytical performance with a kappa statistic of 0.65 and r(2)=0.937.
• A significant difference (p<0.0005) was observed in diabetes control classification for 22.8% of patients.
• The IFCC method, converted to NGSP values, differed significantly from the NGSP-certified method.

Conclusions:

• The IFCC and NGSP methods for HbA1c measurement yield non-interchangeable results.
• The observed differences are substantial enough to impact clinical decisions.
• The scientifically superior IFCC method should replace the NGSP method, requiring new HbA1c targets for diabetes management.