The negative interference caused by
haemolysis in manual
bilirubin assays contrasts with the positive interference reported for some automated methods utilizing the same basic chemistry. A comparison was therefore made of the
haemolysis interference associated with several automated
bilirubin methodologies: multilayer film (Kodak Ektachem- total
bilirubin (TBil), direct
bilirubin (DBil), conjugated
bilirubin (Bc), unconjugated
bilirubin (Bu),; tableted
reagents (Baxter
Paramax- TBil, DBil); continuous flow (Technicon SMAC - TBil). Thirty serum pools were analysed (five concentrations of
bilirubin, 2-229 mumol/l; six concentrations of haemoglobin, 0.00002-0.052 mmol/1). All methods, except one (Bc), exhibited both positive and negative interference, depending upon the relative haemoglobin and
bilirubin concentrations. This interference, at any given haemoglobin concentration, was neither constant nor proportional with increasing
bilirubin concentration. These complex patterns of interference suggest that the best characterization of interference is obtained when (1) both percentage-difference and absolute-difference 'interferographs' are plotted; and (2) the interference is determined at multiple analyte concentrations.