Assessment of five quantitative methods for determination of total proteins in urine

1. We assessed five quantitative methods for the determination of urinary total proteins, three of them with precipitation followed by spectrophotomollowed by spectrophotometry (Tsuchyga/Benedict, Tsuchyga/Biuret and TCA/Biuret); one with gel-filtration (Sephadex G50/Biuret) and a Turbidimetric procedure (SSA). 2. Day-to-day precision was between 3.58 %CV (Tsuchyga/Benedict) and 11.46 %CV (Sephadex/Biuret). The Tsuchyga/Benedict method showed the closest values to controls quantitated by the Kjeldahl method and the lowest detection limit )17.3 mg of total proteins per liter). Recovery studies showed that a level of 100-200 mg/l the Tsuchyga/Benedict recovered over the 96% of the protein added. 3. Comparison studies of 66 24-hour urine samples showed that the best correlation was obtained between the Tsuchyga/Benedict and the Tsuchyga/Biuret methods (r = 0.996). 4. We conclude that the Tsuchyga/Benedict is a sensitive, precise and accurate procedure for the routine quantitation of urinary total proteins.