Parameters indicative of absorption and biological effect in new lead exposure: a prospective study.

Parameters indicative of absorption and biological effect in new lead exposure: a prospective study. Determinations have been made of the blood and urinary lead concentrations (Pb-B, Pb-U), haemoglobin concentrations (Hb), packed blood cell volumes (Hcr), urinary 8-aminolevulinic acid (ALA-U) and coproporphyrin concentrations (CP-U), as well as erythrocyte 8-aminolevulinic acid dehydratase activities (ALA-D), in respect of 33 workers entering occupational lead exposure for the first time in their lives. In a follow-up study lasting from one to four months samples were taken before exposure began, initially at intervals of two days and subsequently at intervals of one to two weeks. Nine control subjects were studied for Pb-B once, and for Hb, Hcr, and ALA-D weekly. The Pb-B rose and the ALA-D activity fell with no demonstrable time lag, while the latency periods of ALA-U, Pb-U, and CP-U were about two weeks. All of these laboratory tests reached a steady state during the follow-up. ALA-D showed the highest correlation to Pb-B and proved to be the most sensitive indicator of lead effect. Both CP-U and ALA-U were useful indicators of the effect of lead upon the organism, although a stepwise regression analysis, and their correlation coefficients with Pb-B, led to the conclusion that CP-U had better explaining power than ALA-U. The mean Hb and Hcr values were significantly lower at the end of the observation period than at the beginning, providing an indication that anaemia begins to develop early in the course of lead absorption. The relative value of various laboratory tests for the diagnosis and prevention of lead poisoning has aroused debate. The opinion today is that the concentration of lead in the blood (Pb-B) is superior to that in the urine (Pb-U) in the reflection of current exposure, while the amount of coproporphyrin (CP-U) or 8-aminolevulinic acid (ALA-U) excreted into the urine best reflects the biological response These tests have giadually replaced the counting of stippled erythro-cytes or reticulocytes in examinations of lead workers. However, another classical test, the haemo-globin value (Hb), is still commonly applied for both preventive and diagnostic purposes, although it is nonspecific and displays a poor correlation, if any, with other 'lead tests' (Williams, 1966). No agreement has yet been reached on the relative merits of ALA-U and CP-U. Most authors recommend the former by reason of its greater sensitivity