Identification and incidence of a urinary fragment of IgG.

Urine from some patients, when concentrated approximately three hundred fold and immunoelectrophoresed against anti-IgG, shows an unexpected additional precipitin line in the alpha-globulin region. This reaction has been shown to be due to the presence of a low molecular weight (approximately 20 000) fragment of the heavy chain of IgG. A retrospective examination of immunoelectrophoretic plates run over a period of five years has revealed that this fragment was present in 30 out of 110 patients.