How reliable are human hair reference intervals for trace elements?

Inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination of major and trace element concentrations in scalp hair samples from a population group (N=1091) of Rio de Janeiro city. From these results, preliminary `normalʹ or reference intervals were calculated which are for several trace elements (e.g. B, V, Co, Ge, Mo, Au, As, Se, Sb, Th), but also for some minor elements (e.g. Ca, Mg) in disaccord with data published by five clinical laboratories which used inductively coupled plasma atomic emission spectrometry (ICP-AES). The limitations of ICP-AES in routine hair analysis is shown by comparison of detection limits for both methods and by results from two laboratory intercomparison exercises. It is evident from these data that published reference intervals have to be used with extreme caution and that their urgent revision, based on reliable data produced by the ICP-MS technique, is of extreme importance.