Relationship between serum unconjugated bilirubin levels and the autofluorescence of white blood cells in neonatal jaundice.

In this study, using flow cytometry, we investigated the autofluorescence emitted by lymphocytes, monocytes and neutrophils exposed to different unconjugated bilirubin concentrations and investigated the relationship between these parameters. Different unconjugated bilirubin concentrations were prepared from a newborn serum with an unconjugated bilirubin concentration of 800 m mumol/l. The same concentrations of unconjugated bilirubin have been prepared from pure bilirubin. 10 microliters of cord blood were incubated at room temperature for 15 min with 90-microliter solutions with different bilirubin concentrations prepared from both serum and pure bilirubin. After incubation, cells were washed three times with PBS, erythrocytes were lysed by lysing buffer and run through flow cytometry immediately. Autofluorescence was measured by recording mean fluorescence channels for lymphocytes, monocytes and neutrophils. There was a good correlation between serum concentrations of unconjugated bilirubin that cells were exposed to and the autofluorescence intensity of neutrophils (r = 0.904, p < 0.005), monocytes (r = 0.759, p < 0.05) and lymphocytes (r = 0.766, p < 0.01). Results obtained with pure bilirubin were also similar. Autofluorescence emitted by lymphocytes was lower than that of monocytes (p < 0.01) or neutrophils (p < 0.0005).