The presence of bilirubin in the blood, where it is normally present in relatively small amounts; the term is usually used in relation to increased concentrations observed in various pathologic conditions with excessive destruction of erythrocytes or interference with the mechanism of excretion in the bile. Determination of the quantity of bilirubin in the blood serum reveals two fractions, namely direct reacting (conjugated) and indirect reacting (nonconjugated) bilirubin; determination of conjugated and total bilirubin in serum is an important and frequently used clinical laboratory test. [bilirubin + G. haima, blood]