Reference intervals for blood lead and evaluation of zinc protoporphyrin as a screening test for lead toxicity

We evaluated, retrospectively, 2921 blood samples for the distribution of blood lead values in children below age 16, and in adult female and male subjects. An upper reference value for children and females at 0.48 mumol/L, and for males at 0.72 mumol/L is used. Over 70% of the adult males and > 80% of the children and adult females were within these reference limits, and considered to be at low risk for lead toxicity. The diagnostic utility of zinc protoporphyrin (ZPP) to screen for a positive blood lead result was evaluated using receiver operating characteristic (ROC) curves and likelihood ratios (LR). These studies confirmed that ZPP was insensitive for the detection of elevated blood lead at the critical thresholds of 0.48-1.21 mumol/L in children and adult females with subclinical lead poisoning. ZPP was more diagnostically useful for screening the higher lead-exposed adult male occupational worker.