An automated biochemical assay for haptoglobin: Prevention of interferencefrom albumin

Measurement of the acute phase serum protein, haptoglobin (Hp), is performe d by biochemical methods based on haemoglobin binding, in many veterinary d iagnostic laboratories. During attempts to develop a robust biochemical ass ay for serum Hp it was discovered that serum albumin interfered with the as say system increasing results by as much as 0.28 mg/ml, which could affect interpretation of results especially in species with low normal Hp concentr ations. A reagent cocktail (SB-7) was devised which inhibited the interferi ng effect of albumin. An automated assay for Hp utilising SB-7 was develope d for production as a biochemical assay kit and was evaluated for use in ve terinary diagnosis. The intra-assay coefficients of variation were of 0.9%, 0.9% and 1.3% for Hp concentrations of 2.0, 1.0 and 0.23 mg/ml, respective ly and interassay coefficients of variation of 1.7% and 4.5% for Hp of 2.08 mg/ml and 0.24 mg/ml, respectively. The lower Limit of detection of was 0. 02 mg/ml, linearity extended to 8 mg/ml and recovery was 101+/-7% (mean +/- SD). The assay had correlation coefficients (R-2) of 0.96 and 0.90 when co mpared with immunodiffusion assays of canine Hp and bovine Hp, respectively . Lipaemia and bilirubinaemia caused no interference. Haemolysis did not af fect measurement of low levels of Hp, but at serum Hp concentrations of 0.4 and 1.8 mg/ml the apparent Hp concentration was decreased. Elevated concen trations of Hp were measured in cattle with mastitis, dogs with polyarthrit is and rats experimentally infected with Bordetella pertussis. The automate d assay is precise and has negligible interference from albumin.