Improved method for the adjustment of urinary delta-aminolevulinic acid concentration

The work was aimed at finding whether the ratio of delta-aminolevulinic acid (ALA) and creatinine (Cn) concentration (ALA/Cn), presently used in occupational health practice for evaluation of lead exposure gives a better assessment of ALA excretion than uncorrected ALA concentration itself, as well as at finding a better, but not complicated method for adjustment. ALA and Cn concentrations were measured in untimed urine samples of altogether 390 men and women (age: 18-60 years) not occupationally exposed to lead. In agreement with others, ALA/Cn was found to be an unsuitable method of adjustment for the differences in ALA concentration due to the different concentrations of samples. This can be explained by the different renal handling of ALA and Cn, proved by the literature data. The exponential relationship between ALA/Cn and Cn concentration raised the possibility of adjustment to the logarithm of Cn concentration (ALA/log.Cn). This simple method provided a more reliable index, the value of which was independent of the actual Cn concentration of urines within a wide range (2-32 mmol/liter). The recommended biological limit value (70 mumol/log.Cn mmol) separates equally well from normal values, both in dilute and concentrated urines. The evaluation of occupational lead exposure might be more reliable using this index, instead of uncorrected ALA concentration or the ALA/Cn ratio.