Use of commercially prepared control sera as quality control materials for spectrophotometric bilirubin determinations in amniotic fluid.

The visible absorption spectra of dilutions of commercially prepared chemistry control sera closely mimic those of jaundiced amniotic fluids in cases of fetal rhesus isoimmunization. The authors have assessed the use of these materials for the quality control of net absorbance measurements at 450 nm on amniotic fluids. The authors conclude that they are excellent quality control materials because of their ready availability, low cost, long-term stability, wide range of bilirubin concentrations, and their close resemblance to jaundiced amniotic fluids with respect to light absorption and scattering, sensitivity to light, and pigment extractability into chloroform. Their spectra also contain a maximum at 410 nm, so these materials can also be used as controls for net absorbance measurements at 410 nm, a determination that indicates the extent of heme or meconium pigment interference with net absorbance measurements at 450 nm. These materials both supplement and complement the requisite spectrophotometric performance checks of wavelength calibration and photometric accuracy.