Erythrocyte delta-aminolevulinic acid dehydratase activity as a measure of lead exposure.

The measurement of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) activity has been found to be a useful guide to lead exposure for screening purposes. The pH of the test should be well-controlled for adequate clinical interpretation. False-normal tests are rare even with iron-deficiency anemia or macrocytosis. Recent transfusion and recent bleeding or hemolysis with reticulocytosis tend to invalidate the test. ALA-D activity above 600 International Units effectively excludes significant lead exposure and eliminates the need for further testing. ALA-D activity is maximally depressed at a red cell lead concentration of 200 mug per 100 ml. When activity is moderately depressed, interpretation is difficult and the urinary excretion of lead after the administration of a chelating agent is usually required to differentiate the degree and significance of lead exposure.