The Kodak Ektachem clinical chemistry slide for measurement of bilirubin in newborns: principles and performance.

In this slide, unconjugated bilirubin and its sugar conjugates interact with a cationic polymeric mordant to form spectrally enhanced complexes having similar absorptivities at approximately 400 nm. With reflection densitometry and appropriate mathematical transformation, readings at this wavelength are linearly related to bilirubin concentrations up to 260 mg/L. The slide requires 10 microL of serum, is precise (total CV less than 2% determined over 20 days for the analyte range 39-184 mg/L), gives results that correlate well with the Doumas et al. modification of the Jendrassik-Gróf method (slope 0.95, intercept 0.3, Sy . x 3.4, r = 0.991), and is relatively interference free. Also, the slide measures less loss of bilirubin after in vitro illumination of serum specimens than do diazo tests. An intermediate layer in the slide minimizes the spectral interference from hemoglobin and prevents the detection of the strongly protein-linked ("delta") bilirubin found in many jaundiced adults. The method is recommended for newborns (less than or equal to 14 days), in whom the incidence of delta bilirubin is negligible.