Critical Assessment of the Diagnostic Value of Feline α₁-Acid Glycoprotein for Feline Infectious Peritonitis Using the Likelihood Ratios Approach

Abstract

Alpha-1-acid glycoprotein (AGP) increases in the blood of cats with feline infectious peritonitis (FIP), a lethal disease caused by feline coronavirus (FCoV). However, the diagnostic potential of AGP might be limited because AGP also increases in pathophysiological conditions other than FIP. In this retrospective study, the diagnostic potential of serum AGP concentration was evaluated on the basis of the pretest probability of disease, according to the Bayesian approach. Serum AGP levels from cats with FIP (group 1; n = 58) and without FIP (group 2; n = 104) were evaluated. Non-FIP cats were further subgrouped as follows: 2a) inflammation (n = 26), 2b) asymptomatic FCoV infection (n = 49), 2c) injection-site sarcoma (n = 19), 2d) postvaccination (n = 7), and 2e) specific pathogen free (n = 3). Standard descriptive analyses by group and empirical receiver-operating characteristic (ROC) curve estimation were performed. Ordinary logistic regression analysis was performed to derive an estimate of the continuous likelihood ratio to produce the posttest probability of disease for any combination of pretest probability and serum AGP value. The comparison of serum AGP levels in the different groups and the analysis of the ROC curve confirmed that serum AGP is a powerful discriminating marker for FIP. The Bayesian approach demonstrated that when the pretest probability of FIP is high, based on history and clinical signs (groups 1 or 2a), moderate serum AGP levels (1.5-2 mg/ml) can discriminate cats with FIP from others, while only high serum AGP levels (>3 mg/ml) can support a diagnosis of FIP in cats with a low pretest probability of disease (groups 2b to 2e).

Diagnosis of Feline Infectious Peritonitis: A Review of the Current Literature

“…Cats with FIP often exhibit markedly increased concentrations of acute phase proteins (APP), such as alpha-1-acid glycoprotein (AGP), serum amyloid A (SAA) or haptoglobin in serum [11,25,26,27,28]. Still, although these parameters can help in establishing a diagnosis and a negative AGP measurement can potentially exclude FIP [15], on their own, they are not pathognomonic for FIP.…”

“…Increased concentrations of APP can also be found in cats with various other inflammatory conditions, neoplasia or even in healthy FECV-infected cats [25,26,27,29,30,31,32]. As was stated before for hematological and serum biochemical parameters, measurement of APP, such as AGP, can only be helpful when interpreted together with other abnormalities in order to provide an index of suspicion of FIP in an individual cat [28].…”

Diagnostic Methods for Feline Coronavirus: A Review

“…SAA and fAGP concentrations increase in FIP, but they are not specific for this disease. While moderately elevated levels of acute-phase proteins are found in several inflammatory conditions, high levels of fAGP (>1.5 g/L) and SAA in plasma or effusions can indicate FIP and may be useful supportive tests [38][39][40][41].…”

Pharmacokinetic Profile of Oral Administration of Mefloquine to Clinically Normal Cats: A Preliminary In-Vivo Study of a Potential Treatment for Feline Infectious Peritonitis (FIP)

“…The increase in AGP in malaria is thought to result in increased mefloquine plasma protein binding, thus affecting the apparent volume of distribution [ 61 ]. High levels of AGP have been demonstrated in experimentally induced FIP [ 63 ] and naturally infected FIP cats [ 64 , 65 ], and is commonly used as a diagnostic tool for FIP in practice [ 66 ]. Thus, it is possible that the high level of AGP and potentially other acute phase proteins in FIP infected cats increases mefloquine plasma protein binding, altering the pharmacokinetic profile in these cats.…”