Improved correlation coefficients between indicators of exposure and indicators of effect in lead poisoning

ABSTRACT

The correlation coefficients between concentration of lead in whole blood [mug/100 ml] and urinary coproporphyrin III levels [mug/24 h] were raised to 0.9134 in newly exposed and to 0.9051 in highly exposed subjects, when determinate errors were eliminated. The sampling step was arbitrarily re-defined on the basis of the lead metabolic model to include two sampling conditions [the non-steady state and the steady state conditions]. While, during exposure, when values of lead in blood were not stable, the levels 7 days after cessation of exposure reflected the steady state conditions and proved more valuable in evaluating the extent of exposure. Furthermore, the determinate error in the assay of urinary coproporphyrin III, which originated from the incomplete oxidation of porphyrinogens, was also eliminated after incorporating on oxidation step prior to the chromatographic determination of the porphyrin profiles. As a result a 20.6 to 50.3% increase in the values of coproporphyrin III was observed. When the above errors were corrected, correlation coefficients improved both in low, medium and high exposure cases