A Riboflavin Assay Suitable for Clinical Use and Nutritional Surveys

Abstract

A protozoological assay based on the ciliate Tetrahymena pyriformis for total riboflavin in human and rat biologic fluids and tissues is described. The method is sensitive and specific for riboflavin. Its simplicity compared to other methods recommends it for investigative and nutritional surveys involving riboflavin. As in man and animals, galactoflavin competitively inhibited riboflavin utilization by T. pyriformis. Five patients on a food- and vitamin-deprived regimen had deficient circulating riboflavin levels after five months, indicating that adequate riboflavin is available for at least this long. This method can also be used to assess tissue riboflavin stores by determining the half-clearance time of intravenously administered riboflavin. "Normal" mean values for whole blood, based on 798 randomly selected patients with histories of good diet, was 200 ± 85 ng. per ml.; patients with histories of poor nutrition averaged below 80 ng. per ml.