The urinary excretion of δ-aminolevulinic acid has been widely used as a measure of the biological effect of lead in lead exposed workers. It is usually measured by colorimetric method based on the color reaction of ALA-pyrrole with Ehrlich´s reagent. But the results of δ-ALA in urine by this method are somewhat artificially higher than expected due to the urinary ALA-like compound such as aminoacetone. On the other hand, the recently developed fluorometric HPLC method is very sensitive and specific for the measuring urinary ALA. In order to compare the data obtained by two methods and to investigate the interrelation between two methods, 117 lead workers with different lead exposure were checked urinary δ-ALA, blood lead and other lead exposure related indices. The results obtained are as follows:
1. Urinary excretion of δ-ALA by colorimetric method is 2.15 times higher than HPLC method in overall, revealing 2.47 times in workers of blood lead less than 20㎍/㎗, 2.53 times in workers of blood lead 21-40㎍/㎗ and 1.86 times in workers of blood lead over 41㎍/㎗, respectively.
2. While the correlation coefficients of δ-ALA measured by colorimetric method with blood lead and blood ZPP was 0.571 and 0.629, those of δ-ALA measured by HPLC with blood lead and blood ZPP were 0.610 and 0.637. All the correlation coefficients were statistically significant, but there was no statistical difference of correlation coefficients between two methods.
3. The correlation coefficient of urinary excretion of δ-ALA between two method was 0.838 without any correction, but it was 0.852 with the correction of specific gravity 1.024.
4. Simple linear regression of δ-ALA measured by HPLC method on δ-ALA measured by colorimetric method was (ALA-UPH) =-0.245+0.536 (ALA-UCO) without any correction and it was (SP ALA)=-0.525+0.598 (SP ALA-UCO) with the correction of specific gravity 1.024.
With above results, it is recommended that the diagnostic criteria of δ-ALA for lead poisoning needed to be revised if δ-ALA is measured by HPLC rather than colorimetric method.
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