A Functional Turbidimetric Method to Determine C-Reactive Protein in Horses

A turbidimetric method to determine serum C-reactive protein (CRP) concentration, based on soybean oil-phosphocholine interaction, was performed on horse serum samples to evaluate its potential diagnostic value in veterinary medicine. Intralipid 20% in 0.1 M Tris-calcium buffer (pH 7.5) was added to horse serum. After 30 min of incubation at 37 °C, the CRP-phosphocholine complexes were turbidimetrically, bichromatically (660 nm/700 nm) quantified on a commercial analyzer. Furthermore, comparison between CRP and other inflammatory markers, including white blood cell and neutrophil counts, was performed to evaluate the diagnostic value of both tests. Standardization of the assay was done using a commercial human CRP calibrator. The CRP measurements were performed on serum samples (296 patients and 34 controls). Reference values were found to be lower than 10 mg/l. The method was found to be linear between 1 and 400 mg/l. A moderate correlation was observed between CRP values and the relative neutrophil counts. Receiver-operating characteristics analysis demonstrated the area under the curve for CRP was 0.928, which was superior (P < 0.001) to the neutrophil count (0.804) and the leukocyte count (0.664) in detecting the presence of inflammation. This CRP assay showed reliable results as an acute phase test in horses, confirming its species-independent capability to detect CRP in various mammals, including horses.