Short and medium term stability of biomarkers of inflammation and in vivo oxidation in biological fluids of healthy Guatemalan men

Over a period of 9 wks, in 8 healthy Guatemalan male volunteers, we serially measured serum levels of interleukin‐4 (IL‐4) and tumor necrosis factor (TNF‐α) (markers of inflammation) and urinary excretion of thiobarbituric acid reactive substances (TBARS), isoprostanes (ISO), and 8OH‐deoxy‐guanosine at baseline and 1, 2, and 7 days after oral doses of iron: 0, 15, 30, 60, 120 and 240 mg given as single doses at 1‐wk (0–60 mg) or 2‐wk (120, 240 mg) intervals In most instances, serum IL‐4 was below the detection limit. Intraindividual CVs for baseline TNF‐α ranged from 13.6–46.7% (mean, 24.1%) over 6 samplings. For 6 consecutive urinary measures, the baseline within‐individual CVs ranged from 23.4–74.9% (mean, 37.3%) for TBARS, 13.4–149.7% (mean, 63.2%) for ISO, and 35.2–77.3% (mean, 49.7%) for 8OhdG. With respect to within‐group stability, increasing iron dosage had no consistent effect on the variance of any of the 2 circulating inflammatory or 3 urinary oxidation biomarkers. These intra‐ and inter‐subject variation analyses inform the estimation of critical sample‐size for the design of prospective intervention trials using the respective modern biomarkers as outcome variables.