Detection of serum haptoglobin by enzyme-linked immunosorbent assay in cows with fatty liver.

Haptoglobin cannot be detected in the serum of healthy cattle by the haemoglobin-binding assay or single radial immunodiffusion. The present study was designed to examine whether an enzyme-linked immunosorbent assay could be applied to measure serum haptoglobin concentrations in healthy cows and in cows with fatty liver. When either purified cow haptoglobin or haptoglobin-positive serum were used as the antigen in the assay, the standard curves obtained were distinctly different, and haptoglobin in serum was detected more sensitively than the purified protein. The addition of bovine serum albumin to purified haptoglobin shifted the curve towards that obtained with haptoglobin-positive serum, suggesting that an interaction with serum albumin was partly responsible for the different standard curves. By use of the standard curve for haptoglobin in serum, the mean (SEM) concentration of haptoglobin in samples from four cows with fatty liver was 466 (147) micrograms ml-1, but the sera from four apparently healthy cows contained less than 0.01 microgram ml-1 haptoglobin.