Formate in urine as a biological indicator of formaldehyde exposure: a review

The presence of a small amount of endogenously derived formate in human urine is normal; however, formate derived from the metabolism of formaldehyde, several other industrial compounds and some pharmaceuticals may elevate the urine formate concentration above the normally expected values. This elevation in the urine formate concentration presents the possibility of using this as a tool for monitoring exposure to chemicals. Unfortunately, the use of urine formate as a technique for monitoring personal chemical exposure has yet to be evaluated. This review identifies several potentially important variables that could alter the extent to which formate is eliminated through the urine and that could affect the accuracy of using urine formate concentration as an indicator of chemical exposure. Some potentially important confounders that have been identified, but not evaluated adequately, include dietary intake, nutritional status and exposure to cigarette smoke. Furthermore, the metabolism and elimination kinetics have yet to be adequately demonstrated in humans. Without having controlled for potential confounders in previous pharmacokinetic studies, it is unknown whether or not the large range and variation observed in human studies is due to the confounders or to innate individual variability. Given the poor understanding of the normal variation of formate concentration in the urine, the use of it as a biological indicator of chemical exposure becomes questionable. Without appreciable skin penetration, as in this case, the reliance upon air monitoring alone may be more practical. The evidence at this time suggests that the use of urine formate to monitor chemical exposure offers a broad opportunity for investigative research. At the present time, however, the interpretation of urine formate concentration in samples obtained from workers would be difficult.