Immunoglobulin light chain staining of lymph node biopsies: an interlaboratory comparison

In recent years, the demonstration of cell surface or cytoplasmic monoclonal immunoglobulin kappa or lambda light chains in lymphoid tissues has been considered evidence of their B-cell origin. In an effort to evaluate the reproducibility of results among various laboratories performing immunoperoxidase immunostaining of lymph node specimens, 12 lymph node biopsies were similarly fixed and processed, and serial sections submitted to four laboratories for staining by the unlabelled antibody (peroxidase-antiperoxidase conjugate) technique. Seven of these were malignant lymphomas four were negative, and one was metastatic carcinoma. Participants were not told the diagnosis and were asked to evaluate each specimen for the presence of monoclonal light chain staining. While the overall agreement in results were good, one of four laboratories differed from the other three in four out of the 12 cases. The significance of this finding and its implications are discussed.