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To the Editor: Dr Schett and colleagues¹ reported that a low level of the receptor activator of nuclear factor B ligand (RANKL) is an independent predictor of nontraumatic fracture and that it may gain relevance for assessment of fracture risk. However, the study has several weaknesses, and important information is missing.

First, the study is based on what appears to be an untested laboratory method. Soluble RANKL levels in normal serum are extremely low, in the (sub)picomolar range. According to Schett et al, RANKL was measured "by a commercial sandwich enzyme-linked immunosorbent assay [ELISA] (Biomedica, Vienna, Austria) as described [in their reference 12]." In contrast with Biomedica's OPG ELISA, I have not been able to find any references to publications using this product or showing validity and reliability on Biomedica's Web site, and it is not mentioned in the article's reference 12, which describes immunoprecipitation of murine RANKL. In addition, . . . [Full Text of this Article]

Håkan Melhus, MD, PhD
hakan.melhus@medsci.uu.se
Uppsala University Hospital
Uppsala, Sweden

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