the conversion factor for SI units: 1 μg/dl = 0.04826
μmol/L. Lead in bovine blood (SRM 955b, National
Institute of Standards and Technology) was used as the
standard reference. The laboratory participates in quality
control programs were the Inter Laboratory Program of
Quality Control at Zaragoza, Spain, and the Wisconsin
State Laboratory of Hygiene Program (WSLH).
Other biochemical analyses
Hemoglobin (Hb) was analyzed using a Hemocue
Photometer (Hemocue AB). Zinc protoporphyrin (ZPP)
was tested in whole blood at the school with ZP Hematofluorometer
(AVIV Biomedical).