Direct bilirubin assays are laboratory tests used to measure the concentration of direct bilirubin in blood serum or plasma. Bilirubin is a yellowish pigment produced by the breakdown of heme, a component of hemoglobin from red blood cells. Direct bilirubin specifically refers to the portion of bilirubin that has been conjugated with glucuronic acid in the liver, making it water-soluble and capable of being excreted into bile.
Direct bilirubin assays typically utilize colorimetric or enzymatic methods to quantify the concentration of direct bilirubin in biological samples.
Colorimetric assays often involve the use of reagents that react with direct bilirubin to produce a color change, which can be measured spectrophotometrically. Enzymatic assays utilize enzymes such as bilirubin oxidase or diazo reagents to catalyze reactions that generate a measurable signal proportional to the concentration of direct bilirubin.
Direct bilirubin assays are typically performed alongside total bilirubin assays, which measure both direct and indirect (unconjugated) bilirubin levels.