Establishing albumin levels in sheep serum by a specific fluoroimmunoassay

A rapid and sensitive fluoroimmunoassay (FIA) was developed to measure albumin levels in sheep serum. The assay employed ovine albumin labelled with fluorescein as the tracer and a rabbit antiserum raised against sheep albumin. Separation of antibody-bound from free albumin was achieved using a second antiserum directed against the Fc component of rabbit IgG. Assay procedures were simplified by mixing the two antisera prior to use. Satisfactory assay validation parameters were demonstrated and the reagents were stable for at least 1 year at 4 degrees C. In contrast to the bromocresol green dye binding method, the accuracy of the FIA was unaffected by contaminating immunoglobulins. The FIA was used to establish reference ranges for serum albumin levels in lambs, in normal ewes and in ewes undergoing a prolonged course of immunisation. Mean serum albumin levels for these three groups were 38.8, 51.3 and 37.8 gL-1 respectively. The sensitivity of the assay makes it suitable to monitor albumin levels in therapeutic products derived from sheep blood or serum.