[Standardization of the values of the concentration of exogenous substances in the urine and expired air].

Abstract

Workplace pollutants, inhaled by exposed people, can be subsequently excreted by the kidney as biotransformed or by the lung as parent substances. In both cases the concentration values need to be corrected to a given hydration level (the urinary metabolites) or to a value adjusting the effects of respiratory manoeuvres and those of the mixing between alveolar and dead space air (the volatile substances eliminated through the respiratory tract). The classical methods of standardization of urinary values lie in expressing the data as a value adjusted to a constant specific gravity of urine (1.020) or as a creatinine-adjusted concentration (amount of a compound in urine per gram of urinary creatinine). In the light of the recent researches, such adjustment would not be sufficient to correct the effects of the variability due to urinary volume or flow rate. New formulas to standardize the crude values of urinary concentration have been proposed; such adjustment should be more suitable. The concentration of volatile compounds present in expiratory air samples can be modified by hyperventilation or hypoventilation during sampling manoeuvres (1st factor) and by the mixing between dead space and alveolar air (2nd factor). These two factors similarly affect the CO2 concentration or CO2 partial pressure. Then, a proper standardization of the concentration of the pollutants in expired air samples might be their adjustment to a value corresponding to the normal level of alveolar CO2 partial pressure (PACO2 = 40 mmHg) or alveolar CO2 concentration (FACO2 approximately 0.055 or 5.5%).