Staining method for kidney biopsy image

[Two of the authors respond:]

We thank Henry Schneiderman for his comments on the stain we used to demonstrate the calcium deposits in the tubular lumina of our patient's kidney.¹ Schneiderman is right, of course, and we appreciate his meticulous and observant reading of our paper.

We made a special effort to use the von Kossa staining method for this kidney biopsy. This staining method is used as a histochemical method for calcium, but it is really a method for phosphate and carbonate. The calcium in the tissue section is replaced by silver; in the presence of phosphate and carbonate the silver is reduced to form crystals of silver phosphate and silver carbonate, which appear black and have a unique appearance in histologic sections. Figure 1 shows the 2 staining methods we used for our patient's kidney biopsy, which produced clearly different results. Hematoxylin–eosin staining was mentioned in our article by mistake; we apologize for this error.

Figure 1: A kidney biopsy showing tubular atrophy and multiple calcium deposits (original magnification × 400) stained with hematoxylin–eosin stain (top) and von Kossa stain (bottom).