Factitious proteinuria: diagnosis and protein identification by use of isoelectric focusing.

Factitious proteinuria is an unusual finding. We present a case in which clinical suspicion was aroused by the disparity between the clinical history and findings and the 24-h excretion of protein in urine. Electrophoresis of the patient's serum and urine confirmed the presence of an unusual protein. By isoelectric focusing we identified it as egg-white, a finding confirmed by immunofixation with antiserum to egg-albumen. In the past, confirmation of the identity of such a protein has required specific antiserum for immunofixation or immunodiffusion. Such antiserum may not always be available. However, isoelectric focusing gives sufficient resolution for positive identification of exogenous proteins, even in the presence of true proteinuria.