Glycation index of hair for non-invasive estimation of diabetic control

We propose a new indicator for diabetic control that shows the extent of glycation of hair protein (keratin), the glycation index (A(390)/A(412)) which is based on the ratio of glycated protein- to cystine-induced coloration, where A(390) and A(412) represent each absorbance in the color reactions of glycated protein and cystine in the hair protein. Samples can be quickly and non-invasively collected and easily stored. This index for the back and scalp hairs from hypercholesterolemic mice with hyperglycemia, diabetic rats and diabetic patients gave significantly higher values (2.0-6.0-fold) than those of normal subjects (p<0.01). The glycation indices (mean + or - S.D.) of hairs from diabetic and non-diabetic subjects were 3.00 + or - 0.96 (n = 21) and 1.51 + or - 0.45 (n = 30), respectively. These indices (y) correlated well with the levels of glycohemoglobin (HbA(1c), chi) in diabetic and non-diabetic subjects: y = 0.69 chi- 2.03 (r = 0.82, n = 31, p<0.01). Within-run precision (reproducibility, CV) for the assay of the glycation indices of hairs from the three groups was 6.7-9.4% (n = 10 each). The proposed glycation index of hair gave reasonable results for animals and humans with normo- and hyperglycemia, suggesting that it is reliable and can be diagnostically useful.