Variability in XRF-measured tibia lead levels

A few studies have examined the variability in Cd-109-based K-shell x-ray f luorescence (KXRF) bone lead measurements from replicate measurements made either at the same time or over a period of time, and one of these studies has shown that the uncertainty in an individual measurement is an underesti mate of the standard deviation of replicate measurements. Variability in KXRF tibia lead measurements was assessed from ten cadaver i ntact legs, from the bare tibiae dissected from nine of these legs, and fro m four in vivo volunteers. Cadaver legs underwent replicate measurements on multiple occasions. In vivo volunteers underwent single measurements of th e left tibia monthly for one year. Average tibia lead levels in the cadaver legs and in vivo volunteers ranged from 6 to 50 and from 6 to 13 mug Pb per g of bone mineral respectively. The factors influencing the standard deviation of replicate measurements we re investigated. Both cadaver and in vivo measurements confirmed that the u ncertainty in an individual measurement is an underestimate of the standard deviation of replicate measurements, suggesting a methodological deficienc y probably shared by most current Cd-109-based K-shell XRF lead measurement systems.