Repeatability of tibia lead measurement by X-Ray fluorescence in a battery-making workforce

The purpose of this study was to remeasure in vivo tibia lead levels in a lead-acid battery manufacturing workforce measured in a previous survey and believed to be unrealistically high. Tibia lead levels were measured by K-shell X-ray fluorescence (XRF) spectroscopy in a stratified random sample (n=40) of the original study group (n=381). The repeat survey showed much lower tibia lead levels (median=54.3 microg lead/g bone mineral, compared to 217.9 microg lead/g bone mineral, n=40). Tibia lead levels were significantly correlated with duration of occupational exposure, zinc protoporphyrin levels, and cumulative blood lead index, but not with current blood lead levels. Thirty-eight of the 40 subjects underwent two consecutive tibia lead measurements to assess the test-retest repeatability of the XRF tibia lead measurement technique. The intraclass correlation coefficient between repeated measurements was 0.926 (P=0.0001). Three measurement pairs differed by more than 20 microg/g. There was no fixed or proportional bias between the two sets of measurements. We conclude that the technique offers a highly repeatable measurement of tibia bone lead. However, care needs to be taken to avoid contamination when performing measurements on active lead workers.