Overt proteinuria was detected in the urine of a potential kidney donor, ul
timately leading to the refusal of the kidneys for transplantation purposes
. Histological examination of the kidneys did not reveal any abnormalities.
Searching for substances that could have interfered with the urinary total
protein assay, the role of infused, modified gelatin plasma expanders was
investigated. We therefore measured the concentration of protein before and
after the addition of various artificial plasma expanders to urine. Only w
hen Biuret reagent or Pyrogallol Red dye were used did we find elevated con
centrations of protein. Other methods, including the turbidimetric assays,
did not detect additional amounts of protein in the spiked urine. We conclu
de that the infusion of modified gelatin solutions may cause apparent prote
inuria. This effect is not observed with starch-based plasma expanders. Cli
nical chemists and clinicians should be aware of this phenomenon and possib
ly repeat the analysis with a different technique.