A Liley graph uses absorbance at 450 nm in amniotic fluid to assess risk of fetal hemolytic disease; what does increasing absorbance indicate?

A Liley graph uses absorbance at 450 nm in amniotic fluid to assess risk of fetal hemolytic disease; what does increasing absorbance indicate?

• A. Decreasing bilirubin
• B. Increasing bilirubin
• C. No change
• D. Measurement error

Answer: (B)

In the Liley graph, the absorbance measured at 450 nm in amniotic fluid reflects the amount of bilirubin present. Bilirubin has a strong absorption peak near 450 nm, so as bilirubin concentration increases due to fetal hemolysis, the sample absorbs more light and the measured absorbance rises. Therefore, increasing absorbance indicates increasing bilirubin levels, which corresponds to a higher risk of fetal hemolytic disease. The other possibilities (less bilirubin, no change, or measurement error) don’t align with the physiological link between bilirubin concentration and the 450 nm absorbance signal.

In the Liley graph, the absorbance measured at 450 nm in amniotic fluid reflects the amount of bilirubin present. Bilirubin has a strong absorption peak near 450 nm, so as bilirubin concentration increases due to fetal hemolysis, the sample absorbs more light and the measured absorbance rises. Therefore, increasing absorbance indicates increasing bilirubin levels, which corresponds to a higher risk of fetal hemolytic disease. The other possibilities (less bilirubin, no change, or measurement error) don’t align with the physiological link between bilirubin concentration and the 450 nm absorbance signal.