A non-competitive chemiluminescence enzyme immunoassay for the equine acute phase protein serum amyloid A (SAA) - a clinically useful inflammatory marker in the horse

A non-competitive chemiluminescence enzyme immunoassay for measuring serum amyloid A (SAA) in equine serum was developed. A polyclonal anti-equine-amy loid A antiserum specific for equine SAA was utilized, and the assay was st andardized using highly purified equine SAA. An acute phase horse serum was calibrated against the purified SAA and was used as standard when running the assay. Serum SAA concentrations in the range of 3-1210 mg/l could be me asured. The reference range of SAA in clinically healthy adult horses was < 7 mg/l. The clinical validation of the assay comprised the SAA responses af ter surgery and experimentally induced aseptic arthritis, and those associa ted with viral and bacterial infections. The SAA response after surgery (ca stration) was consistent, with peak concentrations on day 2 and a return to normal SAA concentrations within eight days. The aseptic arthritis produce d an SAA response with a pattern similar to that seen after surgery, with p eak concentrations of SAA 36-48 h after induction. Seven horses showed a bi phasic pattern, with a second rise in SAA concentrations on day 4 and 5. Al l animals had SAA levels 17 mg/l on day 15. All horses with viral and bacte rial infections had SAA concentrations above 7 mg/l. The ranges of SAA conc entrations following the different types of inflammation overlap, being con sistent with the unspecific nature of the SAA response. This study revealed that SAA is a sensitive and unspecific marker for inflammation, and descri bes the dynamics of the SAA response after standardized and well defined ti ssue damage. (C) 1999 Elsevier Science B.V. All rights reserved.