Towards the measurement of acute phase proteins in saliva in farm conditions: Development and validation of a lateral flow assay for the measurement of C-reactive protein in pigs

Point-of-care diagnostic tests, such as lateral-flow immunoassay (LFIA), have emerged as a fast diagnostic tool in both human and veterinary medicine. In this paper, a gold nanoparticle-based LFIA device was developed for the measurement of C-reactive protein (CRP) in porcine saliva, using a monoclonal anti-porcine CRP antibody. The dilution ratio for the saliva samples was optimized at 1:5 with an assay buffer. The reaction time was optimized to 20 min, since this provided a positive signal with high CRP concentration saliva samples, but a negative result with an assay buffer or samples with a low CRP concentration. Linear results were observed when two samples with a high CRP concentration were serially diluted. Also, a linear relationship was observed with a validated quantitative method. The assay was precise when samples with high CRP concentration were measured five times in a single assay run. No overlap was observed when samples from healthy and diseased animals were analyzed. The LFIA allowed the detection of high CRP concentrations in porcine saliva samples. The intensity of the result was proportional to the CRP concentration obtained with the quantitative method, allowing for the possible use of the test for semiquantitative purposes