Glucocorticoids directly affect spectrophotometry of bilirubin in amniotic fluid

Dexamethasone or prednisolone, added in vitro to bilirubin-containing amniotic fluid, produces a time-dependent decrease in the 450-nm absorbance of the pigment. Neither the chemical determination of bilirubin in amniotic fluid nor the lecithin/sphingomyelin ratio as determined by thin-layer chromatography is affected by these glucocorticoids. The effect probably is not a result of displacement of bilirubin from its binding sites on albumin, because the absorbance of a solution of crystalline bilirubin at 450 nm is unaffected by added bovine serum albumin. Light scattering of amniotic fluid increases slightly when dexamethasone is added, whether or not low concentrations of bilirubin (less than 1.6 mumol/L) are present. Thus the effect on absorbance evidently is not ascribable to supersaturation and formation of a colloidal sol of bilirubin particles. This direct interference of glucocorticoids with the spectrophotometry of bilirubin in amniotic fluid prompts cautious interpretation of such data as an index to the severity of hemolytic disease of the fetus, specifically in cases of Rhesus-isoimmunization that are being treated with glucocorticoids.