Bilirubin in the premature: toxic waste or natural defense?

because contamination of the sample by even small volumes of furosemide significantly affected thyroxine results. The differences in sensitivity to furosemide interference among assays appear to reflect the serum dilution used in each method. This concern may apply to interference from other drugs (e.g., salicylates and fenclofenac) as well as to other assays (e.g., free triiodothyronine). This study does not address the in vivo effect of furosemide administration on thyroxine measurement. Because oral furosemide may influence measurement of the free thyroxine index (4), the time interval between doses of oral furosemide and blood sampling should be considered in result interpretation. Both the Vitros and AxSYM assays use sample volume:total volume ratios greater than the ratio (0.09) used by the assay in that study (4). Thus, it is likely that the in vivo effect from oral furosemide will be even greater in the Vitros and AxSYM assay systems. Furosemide concentrations of 6.6–73.0 mmol/L reported with routine therapeutic doses of furosemide (5) fall within the range of furosemide concentrations examined here. Clinicians thus may need greater awareness to potential interference from drugs such as furosemide when interpreting results from newer free thyroxine assays that use large sample volume:total volume ratios. TSH measurement may be a more useful test for assessing thyroid function in such cases.