A diabetic Caucasian woman presented with discrepantly
low HbA<sub>1c</sub> values compared with her glycaemia. High-performance liquid chromatography (HPLC) analysis disclosed 80% HbA and 20% HbI Philadelphia (16α2 lys → glut). The calculated glycosylation gap from the fructosamine level was 1.2%. The haemoglobin α/β glycation ratios, as
measured by electron spray ionisation mass spectroscopy (ESI-MS), for the patient and her three children also carrying the mutation were decreased by values of 0.56 and 0.51, 0.50 and 0.49, respectively (reference value 0.66).