DELTA-AMINOLEVULINIC-ACID DEHYDRATASE AS AN INDEX OF LEAD TOXICITY - TIME FOR A REAPPRAISAL

delta-Aminolaevulinic acid dehydratase activity is traditionally accep ted as the most sensitive measurable biological index of lead toxicity . We have measured delta-aminolaevulinic acid dehydratase activity and blood lead concentration in 47 healthy controls (A), 42 iron deficien t patients (B) and 38 occupationally exposed to lead subjects (C). Blo od lead levels [($) over bar x (SD)] did not differ between groups A a nd B [0.51 (0.21) and 0.43 (0.19) mu mol L(-1), respectively] while th ose of group C [2.28 (0.56) mu mol L(-1) were significantly higher (P < 0.001) as compared to the controls. delta-Aminolaevulinic acid dehyd ratase activity [($) over bar x (SD)] was significantly increased [359 9 (1909) mu mol L(-1) h(-1)] in group B and decreased in group C [1052 (532) mu mol L(-1) h(-1)] as compared to the controls [2034 (446) mu mol L(-1) h(-1)] (P < 0.001). There was a significantly negative corre lation of logarithm of delta-aminolaevulinic acid dehydratase with lea d in both groups B (P < 0.05) and C (P < 0.001) but not in group A (P = 0.1). delta-Amino-laevulinic acid dehydratase activity had a high sp ecificity (100%) but a low sensitivity (37%) as an index of toxic lead exposure. According to our data the value of delta-aminolaevulinic ac id dehydratase measurement in the diagnosis of lead intoxication is do ubtful in cases with low blood lead levels, while in the presence of i ron deficiency its reliability is further reduced, since low blood lea d levels may be falsely predicted. delta-Aminolaevulinic acid dehydrat ase activity should be restricted only to monitoring cases with modera te or severe lead poisoning.