The aims of this study were to validate a colorimetric method to measure total
sialic acid (
TSA) in feline serum and to investigate the serum concentration of
TSA in clinically healthy cats seronegative (n = 9) and seropositive (n = 48) for feline coronavirus (FCoV), and in cats affected by
feline infectious peritonitis (FIP, n = 28),
tumors (n = 20), or
inflammation (n = 16). The correlation between
TSA and
alpha(1)-acid glycoprotein (AGP) was also investigated. The method employed in this study is precise and accurate at
TSA levels (in mg/L) commonly encountered in feline serum. No significant differences between seropositive (385.6 +/- 192.2 mg/L) and seronegative (433.5 +/- 179.0 mg/L) cats were detectable, suggesting that the simple
infection by FCoVs does not influence
TSA levels. Compared with seropositive controls, the concentration of
TSA was higher in cats with FIP (556.7 +/- 268.3 mg/L, P = 0.003),
tumors (522.5 +/- 294.4 mg/L, P = 0.028), and
inflammation (546.8 +/- 208.3 mg/L, P = 0.018). The discriminating power of
TSA for FIP is moderate (area under the ROC curve = 0.65) and the likelihood ratio is higher than 3.0 only at high
TSA levels. Consequently,
TSA could support a diagnosis of FIP only at extremely high serum concentration (> 800 mg/L) or when the pre-test probability of FIP is high. No correlations were found between the
TSA and AGP concentrations in cats with FIP, suggesting that sialylated
proteins other than AGP are present. Both the antibody titre and the degree of AGP sialylation were negatively correlated with
TSA levels, suggesting that increased
TSA may contribute to reduce the burden of FCoVs.