Creatinine normalization in biological monitoring revisited: the case of 1-hydroxypyrene

To compare the apparent urinary excretion rates of both creatinine and 1-hydroxypyrene (1-OHP) and to assess the value of creatinine normalization for both toxicokinetic analysis and the routine examination of workers.

All urine samples were collected from individuals who had been exposed to polycyclic aromatic hydrocarbons (PAHs), occupationally and non-occupationally, for at least 24 consecutive hours. Urinary creatinine and 1-OHP were determined. 1-OHP excretion rates were expressed either as a function of creatinine excretion rate or as unadjusted values. Theoretical relationships between creatinine-normalized excretion of metabolites and body weight-adjusted inhaled dose were drawn for men with a constant body mass index.

Creatinine excretion rate paralleled 1-OHP excretion rate. The plot of creatinine excretion rate–adjusted excretion rate of 1-OHP vs time led to smooth curves for determination of toxicokinetic parameters. Creatinine normalization was adequate, even for samples with a urinary creatinine concentration below 0.5 g/l or above 3 g/l. A theoretical analysis revealed that men weighing between 50 kg and 100 kg, exposed to a constant dose of a pollutant producing a urinary metabolite excreted by the same mechanism as creatinine, would exhibit a body weight-adjusted dose span of 2 with an accompanying creatinine-normalized metabolite excretion span of 2.23-fold.

The kinetics of creatinine excretion parallels that of 1-OHP, and a creatinine excretion rate–normalized excretion rate of 1-OHP appears to allow for a better determination of the toxicokinetic parameters of 1-OHP urinary excretion. At least in the case of 1-OHP, creatinine normalization seems valid, even for very dilute or very concentrated urine samples. Finally, because creatinine normalization not only compensates for variable diuresis but also correlates better with the body weight-adjusted dose of the parent compound, it should be used in biological monitoring of exposure to (PAHs) pyrene and to other substances whose urinary biomarker excretion kinetics parallel that of creatinine.