The effect of matrix albumin concentration on reduction of NBT by DMF has been investigated together with the effect of cationic additives. Decreased albumin concentration and increased cationic detergent concentration both increased the sensitivity of the assay due to kinetic effects, but addition of a low molecular weight cation had no effect. The reduction of NBT by glycated albumin was not increased in sensitivity by a protein matrix of low concentration. Due to the complexity and poorly understood nature of interaction between DMF and albumin in the reduction of NBT, the authors do not consider DMF to be a suitable primary calibrant for the fructosamine assay.
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