Stainable bone iron in undecalcified, plastic-embedded sections. Occurrence in man related to the presence of "free" iron?

Iron demonstrable with the Prussian blue reaction at the osteoid/mineralized tissue interphase (osteoid seam) of trabecular bone was observed in only 2.3% of a total of 1536 conventionally fixed and processed, undecalcified, plastic-embedded biopsy specimens taken from the iliac crest of patients for various diagnostic purposes. In marked contrast, clearly stainable bone iron was noticed in all 4 biopsy specimens from the iliac crest and in 11 of 15 vertebral bone fragments obtained at autopsy from individuals with verified primary or secondary hemochromatosis. Findings, including results obtained in vitro, suggest that a positive Prussian blue reaction at the surface of trabecular bone signals the presence of low-molecular-weight ("free") iron, which can bind to the osteoid matrix directly, ie, without the help of osteoblasts. Stainable bone iron may thus be a useful criterion for early detection of hemochromatosis and other types of potentially toxic iron overload.