A simple method for quantification of biotinidase activity in dried blood spot and its application to screening of biotinidase deficiency.

A simple and reliable method for quantification of biotinidase (EC.3.5.1.12) activity in dried blood spot was devised by a modification of the colorimetric screening test developed by Heard et al. (1984). The enzyme reaction and hemoglobin denaturation were carried out in a U-bottomed microplate. An aliquot of the reaction solution was transferred to a flat-bottomed microplate. After the coupling reaction was started, the adsorbance was measured in situ by a microplate-reader. Both intra- and inter-assay coefficient of variation (CV) values were less than 10%. Biotinidase activity in dried blood spot showed a good correlation to that in serum (r = 0.912, n = 8). This method was applied in a pilot screening of 18,945 newborns in Sapporo City. No positive results have been obtained as yet.