Healthy worker effect in a cross-sectional study of lead workers.

To study the role lead may play in the development of renal disease, we performed a cross-sectional study of workers at a lead smelting plant. Renal function was defined based on calculated creatinine clearance using the prevalence of values under the 3rd percentile to compare groups. The prevalence of calculated creatinine clearance values under the 3rd percentile in these workers (n = 1782) as a whole was 2.81%, a result comparable to that which has to be expected for the general population. Closer analysis, however, showed significantly lower prevalence of calculated creatinine clearance under the 3rd percentile in certain subgroups of workers. These subgroups were workers between the ages of 30 and 39, workers over the age of 50, and Belgian workers who had worked in the plant for longer than 10 years. We conclude that these observations once more clearly demonstrate a "healthy worker effect" on the measurement of renal function in this work force, a major problem in epidemiologic cross-sectional studies.