Urinary monitoring

The intravenous administration of a second isotopic label can also be used to assess true absorption of the oral isotopic labels for elements that are excreted via the kidneys, such as calcium and magnesium. As in plasma appearance studies, the intravenous label serves as a reference dose. When the second label is infused or injected slowly following administration of the labeled test meal, both labels appear in parallel in serum/plasma. Some of the circulating labels, however, are excreted via the kidneys, during which the amount ratio of the two labels in blood should ideally be preserved. If this is so, a single spot urine sample can be used, at least in theory, to determine the amount ratio of the two labels in serum. As the intravenous dose is known, this ratio can then be converted into the amount of oral label absorbed. As for most stable isotope techniques, this method was originally developed for radiotracers [31] and adapted for stable isotopes in the 1980s [32]. 

A technical difficulty associated with any technique involving the administration of an intravenous label is the matching of the rate of appearance of the intravenous label in blood with that of the oral label, which is hardly possible. As a result, the amount ratio of the two labels changes over time in blood and consequently urine, which translates into a possible bias determined by the point in time at which the urine sample is taken. In theory, this can be controlled by collecting urine over 24 h up to 1 week following isotope administration. In practical terms, the amount ratio in blood might be similar to the true ratio of absorbed oral label to intravenous label at some point in time. This permits, in theory, the use of a single spot urine sample for analysis [33]. 

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The absorbed dose or body burden of chlorpyrifos can be estimated using urinary monitoring data as follows 3... 

Arizona cauliflower scouting represented low crop activities. Five orange harvesters and five lemon tree pruners were tested using concurrent dosimetry and urinary monitoring techniques. The re-entry intervals were 43, 2, and 1 days for the orange harvesters, lemon tree pruners, and scouts, respectively. Re-entry workers were monitored for 5- to 6-hr work days in California and for a 4-hr work day in Florida and Arizona. 

Comparison of exposure levels — total absorbed dose of chlorpyrifos (passive dosimetry vs. urinary monitoring)... 

WILSON L A, WILKINSON K, CREWS H A, DAVIES A M, DICK C S and DUMSDAY V l, Urinary monitoring of saccharin and acesulfame K as biomarkers of exposure to food additives, Food Additives Contaminants 1999 16(6) 227-38. 

Bohn, T., Walczyk, T., Davidsson, L., Pritzkow, W., Klingbeil, P., Vogl, J., and Hurrell, R.F. (2004) Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects. Br. J. Nutr., 91 (1), 113-120. 

Moses MA, Harper J, Folkman J. Doxycycline treatment for lymphangioleiomyomatosis with urinary monitoring for MMPs. N Engl J Med 2006 354(24) 2621-2622. 

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