Elimination of dextran interference in serum protein determinations.

Serum containing dextrans of average molecular weight 40,000 (“Dextran-40”), 70,000 (“Dextran-70”), or 75,000 (“Dextran-75”) become turbid when biuret reagent is added (1, ). This interference has been overcome (3) by first precipitating serum proteins with trichioroacetic acid before applying the biuret reaction. Positive interference of these drugs with the o-toluidine glucose assay has also been described (4). An o-toluidine reagent’ containing ethylene glycol is reported to be usable in the presence of dextrans. We show here that ethylene glycol in the biuret reagent also overcomes dextran interference with serum protein determinations.