Evaluation of methods for the estimation of 5-aminolevulinate dehydratase for a broad range of lead concentrations in the blood of exposed workers.

5-aminolevulinate dehydratase activity was estimated in the blood of 30 lead-exposed workers and 15 control persons, using (I) the method of Tomokuni ((1974) Arch. Environm. Health 29, 274--281) and (II) the European standard method (Berlin & Schaller (1974) Z. Klin. Chem. Klin. Biochem. 12, 389--390). The lead level in the blood was in the range 0--11.6 mumol/l. It was found that the correlation between the activity of 5-aminolevulinate dehydratase and the lead level in blood (up to 4.35 mumol/l) are higher for method I than method II. These two methods only give similar results for the units of 5-aminolevulinate dehydratase activity when the lead concentrations in the blood are low. For higher concentrations of this metal (up to 11.6 mumol/l), a high correlation was obtained (r = -- 0.80) between the 5-aminolevulinate dehydratase activity ratio (enzyme measured at pH 6.8/enzyme measured at pH 6.0; method I) and lead concentrations in the blood.