Evaluation of serum biomarkers C-Reactive Protein, Haptoglobin, and Albumin in diagnostics of primary immune-mediated polyarthritis in dogs Canine primary immune-mediated polyarthritis (IPA-I) is a non-infectious inflammatory joint disease, characterized by synovitis commonly accompanied systemic signs of disease such as lethargy, arthralgia, and fever. Acute phase proteins are used for diagnosis, prognosis and monitoring of therapeutic success in a wide variety of diseases but only limited data is available regarding their use as biomarkers in canine IPA-I. The aim of this prospective study was to measure C-Reactive Protein (CRP), Haptoglobin and Albumin in dogs with IPA-I, to compare them with clinical progression under therapy, and to evaluate their significance in terms of diagnosis, monitoring and prognosis. In total 21 dogs with IPA-I at the Small Animal Clinic of Free University in Berlin were included from October 2014 to December 2019. All included patients had a complete diagnostic workup including arthrocentesis, synovial analysis, complete blood count, blood chemistry, tests for infectious diseases, radiography, sonography and regular follow-up visits. Clinical and laboratory examinations were performed at each follow-up visit, and serum CRP, Haptoglobin and Albumin concentrations were measured. All metric data were checked for normal distribution using the Shapiro-Wilk test and analysed descriptively. Non-parametric tests (Wilcoxon test, Friedman test) were used for non-normally distributed data and parametric tests (T-test, ANOVA) for normally distributed data. The significance level was set at α ≤0.05. The data were analysed graphically using box-whisker plots. All patients were sampled at initial presentation (day 0, T0). Further samples were collected from 20/21 dogs (95.2%) each at day 2-7 (T1) and day 8-14 (T2). In 19/21 dogs (90.5 %), further controls were performed at weeks 3-4 (T3) and from 16/21 dogs (76,2 %) at weeks 5-8 (T4). In 12/21animals (57.1 %), controls occurred later than after 10 weeks. Clinical signs (duration 1-300 days) at initial presentation included fever (20/21, 95.2 %), disturbed general condition (19/20, 90.5 %), lameness (14/21, 66.6 %), increased joint effusion (12/21, 57.1 %), painful manipulation of the joints (13/21, 61.9 %), locally increased temperature of the joints (10/21, 47.6 %), painful manipulation of the spine/flexion of the neck (4/21, 19 %). In 13/21 dogs (61.9 %) radiographs revealed increased capsular/soft tissue radiopacity in at least one joint. Joints with inflammatory changes included: carpus (28/31 punctured joints, 90.3 %), stifle (35/39, 89.7 %), tarsus (24/30, 80 %), elbow (18/23, 78.2 %) and shoulder (2/2). After diagnosis, immunosuppressive therapy with prednisolone was initiated in all dogs. Additionally, ten dogs received additional Leflunomide, three Ciclosporin and one dog Mycophenolate mofetil. All dogs improved clinically. All dogs were examined at T0, 20/21 (95.2 %) at T1 and T2 respectively, 19/21 (90.5 %) at T3 and 16/21 (76.2 %) at T4. CRP was elevated in all dogs at T0 (16-169 mg/l, median [m] 97.1; white blood cell count [WBC] 6.7-64.7 G/l [m 15.5]; Albumin [Alb] 26.1 g/l [SD±3.4]). During the follow-up measurement, CRP concentration decreased from T0 to T4 in all dogs (pweiterlesen