A comparison of different lead biomarkers in their associations with lead-related symptoms

Objectives: To evaluate whether dimercaptosuccinic acid (DMSA)-chelatable l ead, an estimate of current bioavailable lead stores, is a better predictor of lead-related symptoms than are other commonly used lead biomarkers, Met hods: A total of 95 male lead workers from three lead industries (one secon dary lead smelting facility, one polyvinyl chloride-stabilizer manufacturin g plant, and one lead-acid storage battery factory), and 13 workers without occupational lead exposure recruited from an occupational health institute , were studied. Blood lead, blood zinc protoporphyrin (ZPP), 4h DMSA-chelat able lead (after oral administration of 10 mg/kg DMSA), urine lead, and uri nary delta-aminolevulinic acid levels were evaluated as predictors of 15 le ad-related symptoms, assessed by self-administered questionnaire, with line ar and logistic regression controlling for covariates. Total symptoms and s ymptoms in three categories (gastrointestinal. neuromuscular, and general) were evaluated. Results: The mean (SD) 4h DMSA-chelatable lead level was 28 8.7 (167.7) mu g, with a range from 32.4 to 789 mu g in the 95 lead workers . The mean (SD) in the non-exposed subjects was 23.7 (11.5) mu g with a ran ge from 10.5 to 43.5 mu g. Blood lead, blood ZPP, and spot urine lead level s ranged from 21.4 to 78.4 mu g/dl, 40 to 331 mu g/l, and 7.5 to 153.0 mu g /l, respectively, in the lead workers, and from 4.0 to 7.2 mu g/dl, 27 to 5 2 mu g/l, and 2.9 to 15.5 mu g/l in the non-exposed controls, respectively. The overall mean symptom score (SD)I derived as the sum of 0 or 1 point fo r absence or presence of 15 symptoms, of the lead workers was 3.7 (2.0), co mpared to 1.2(1.5) for the non-exposed workers. DMSA-chelatable lead was th e best predictor of symptom scores in both crude and adjusted analyses, com pared with the other biomarkers. Lead workers with DMSA-chelatable lead val ues greater than the median (360.5 mu g) were 6.2 times more likely to have frequent tingling or numbness of the arms or legs and 3.3 times more likel y to have muscle pain than subjects with lower chelatable lead values. Thre e symptoms (tingling or numbness of arm or leg, muscle pain, and feeling ir ritation at the slightest disturbance) evidenced a dose-dependent relations hip with DMSA-chelatable lead levels. Conclusions: DMSA-chelatable lead was found to be the best predictor of lead-related symptoms, particularly of b oth total symptom scores and neuromuscular symptoms, than were the other ot her lead biomarkers.