Measuring urinary glycosaminoglycans in the presence of protein: an improved screening procedure for mucopolysaccharidoses based on dimethylmethylene blue.

Earlier we described a simple and reliable screening procedure in urine for mucopolysaccharidoses based on the color reaction of glycosaminoglycans (GAGs) with dimethylmethylene blue. At physiological concentrations of urinary protein, we observed an obvious interference by protein in the assay. By modifying the assay, we abolished the protein interference. The modified procedure is not disturbed by human serum albumin, IgG (both tested with as much as 5 g/L of protein), or urinary proteins. The modified procedure appeared as reliable as the original. No false-negative results were found in a series of 26 urine samples from patients with mucopolysaccharidoses (sensitivity 100%). In a series of 405 urine samples offered for metabolic screening, 24 samples with increased GAG content and normal GAG composition were seen (specificity 94%). The method may also be applicable for determining GAG in other body fluids or solutions containing protein.