The influence of citrate and phosphate on the Mancini single radial immunodiffusion technique and suggested improvements for the determination of urinary albumin.

When adapting the immediate bromcresol green method for urinary albumin determination a correlation study with the Mancini single radial immunodiffusion (SRID) method was performed. This study showed large disparities between the two methods, SRID giving the higher results. The unsuitability of the currently used SRID methods is demonstrated and improvements to the method are suggested. Known amounts of albumin were added to urine samples as well as to a "synthetic urine", both giving falsely elevated results with the SRID method. On investigating the different components of the "synthetic urine", it was found that the disparities were due to the influence of citrate and phosphate. On addition of citric acid or phosphate to the dilution buffer and/or the gel buffer, the results of the SRID method agreed with those of other methods and with the expected values. The findings presented in this paper can probably be extended to other immunological methods too since it seems to be the antigen-antibody reaction which is affected.