Alpha 1-acid Glycoprotein Decreases Recovery of Total Protein in Urine When Trichloroacetic Acid Is Used to Precipitate the Proteins

Clin Chem. 1990 Mar;36(3):565-7.


Total urine protein was measured in 132 samples by an automated benzethonium chloride method and the Ponceau-S/trichloroacetic acid (PS/TCA) method. Of these, 27% gave a result 0.1 g/L or more higher by the benzethonium chloride method. Of this 27%, most contained an abnormally high concentration of the acute-phase reactant, alpha 1-acid glycoprotein. By assaying urine containing added alpha 1-acid glycoprotein and albumin, we found that alpha 1-acid glycoprotein causes the PS/TCA method to underestimate the total urine protein concentration, whereas the benzethonium chloride method is unaffected. Not all urinary albumin was precipitated by TCA when alpha 1-acid glycoprotein was present. Therefore, protein methods in which trichloroacetic acid is used as a concentrating step before the assay will underestimate total urine protein when the concentration of alpha 1-acid glycoprotein is high.

Publication types

  • Comparative Study

MeSH terms

  • Azo Compounds
  • Benzethonium
  • Chemical Precipitation
  • False Negative Reactions
  • Humans
  • Immunoassay
  • Indicators and Reagents
  • Orosomucoid / urine*
  • Proteinuria / urine*
  • Trichloroacetic Acid*


  • Azo Compounds
  • Indicators and Reagents
  • Orosomucoid
  • Benzethonium
  • Trichloroacetic Acid
  • ponceau S