Clinical Chemistry, Vol 20, 753-760, Copyright © 1974 by the American Association for Clinical Chemistry

Comparison of Four Methods for Determination of -Aminolevulinic Acid in Urine, and Evaluation of Critical Factors

¹ Unité de Toxicologie Industrielle et Médicale, Catholic University of Louvain, Avenue Chapelle-aux-Champs, 4 B-1200 Brussels (Belgium).

Four methods—two requiring ion-exchange chromatography of urine (Mauzerall-Granick; Davis-Andelman) and two omitting the chromatographic step (Grabecki et al.; Lauwerys et al.)—for determination of urinary -aminolevulinic acid (I) have been compared. Experienced analysts obtained a satisfactory coefficient of variation (5%) for each of the four methods. Over the whole concentration range of 0 to 60 mg/liter, both chromatographic methods gave identical results. At concentrations <6 mg/liter, the automated method of Lauwerys et al. gave slightly higher results than did the chromatographic methods. At concentrations >6 mg/liter the values of I obtained with the automated method were almost identical with those yielded by the chromatographic methods, whereas with the method of Grabecki et al. one-third less was found. The results for the automated method correlated better with those for the two chromatographic methods than did those for the method of Grabecki et al. Quality control of prefilled commercially available columns (Bio-Rad) and standard solutions of I (100 µg/ml) gave results with a low variability (<10%). Ionic strength and pH of urine do not influence significantly the determination of I by the automated method, but influence determination of I by the Davis—Andelman method. With or without a preservative, I can be conserved for at least two weeks, if urine is kept at 4 °C. Tartaric acid (1 g/100 ml) or acetic acid (1 ml/100 ml) are satisfactory preservatives for urine stored in darkness at room temperature; sodium azide or thymol are less effective than acidification. During storage the concentration of I in urine decreases as pH increases (above pH 6). Only a moderate effect of natural daylight was observed.

Submitted on March 8, 1974
Accepted on April 30, 1974