Protein-free filtrates obtained by membrane ultrafiltration. Application to the determination of serum constituents.

Serum was ultrafiltered by centrifugation through size-selective membranes, and the ultrafiltrates were analyzed directly for glucose, urea nitrogen, creatmine, and uric acid. The concentrations obtained were equivalent to their concentration in conventional protein-free filtrates. This procedure eliminates the need for specific precipitating methods required in various analyses, and yields undiluted samples that are free of foreign ions.