δ-Aminolaevulinic acid dehydratase as an index of lead toxicity. Time for a reappraisal?

Aminolaevulinic acid dehydratase activity is traditionally accepted as the most sensitive measur- able biological index of lead toxicity. We have mea- sured 6-aminolaevulinic acid dehydratase activity and blood lead concentration in 47 healthy controls (A), 42 iron deficient patients (B) and 38 occupationally exposed to lead subjects (C). Blood lead levels (% (SD)) did not differ between groups A and B (051 (0.21) and 0.43 (0.19) pmol L-I, respectively) while those of group C (2.28 (0.56) pmolL-I were significantly higher (P < 0.001) as compared to the controls. 6-Aminolae- vulinic acid dehydratase activity (X (SD)) was signifi- cantly increased (3599 (1909) pmol L-I h-'1 in group B and decreased in group C (lo52 (532) pmol L-I h-I) as compared to the controls (2034 (446) pmol L-1 h-I) (P < 0.001). There was a significantly negative correla- tion of logarithm of 6-aminolaevulinic acid dehydra- tase with lead in both groups B (P < 0.05) and C (P < 0.001) but not in group A (P = 0.1). &Amino- laevulinic acid dehydratase activity had a high specifi- city (100%) but a low sensitivity (37%) as an index of toxic lead exposure. According to our data the value of 6-aminolaevulinic acid dehydratase measurement in the diagnosis of lead intoxication is doubtful in cases with low blood lead levels, while in the presence of iron deficiency its reliability is further reduced, since low blood lead levels may be falsely predicted. &Amino- laevulinic acid dehydratase activity should be restricted only to monitoring cases with moderate or severe lead poisoning.