Usefulness of serum amyloid A for the diagnosis of pyelonephritis in cats: A prospective evaluation.

Abstract

BACKGROUND: The diagnosis of pyelonephritis in cats is challenging and development of a noninvasive and accurate biomarker is needed. HYPOTHESES: Serum amyloid A (SAA) is increased in cats with pyelonephritis, but not in cats with other urinary tract diseases. ANIMALS: A cohort of 125 cats (149 observations). METHODS: This was a prospective study. Group 1 included cats with a diagnosis of pyelonephritis either confirmed by bacterial culture of pelvic urine (Group 1a) or presumed (1b). Group 2 included cats for which pyelonephritis was ruled out (with certainty: Group 2a or judged unlikely: Group 2b). SAA concentration was compared between groups, and accuracy of SAA for the diagnosis of pyelonephritis was calculated using a Receiver Operating Characteristic (ROC) curve analysis. RESULTS: Median SAA concentration was significantly higher in Group 1a (86.8&#x2009;mg/L [73.3; 161.5]; n&#x2009;=&#x2009;8) than in Group 2a (4&#x2009;mg/L [1.8; 5.6], n&#x2009;=&#x2009;19; P&#x2009;<&#x2009;.001) and in Group 2b (5.4&#x2009;mg/L [3.1; 9.7], n&#x2009;=&#x2009;113; P&#x2009;<&#x2009;.001). It was also significantly higher in Group 1b (98.8&#x2009;mg/L [83.1; 147.3]; n&#x2009;=&#x2009;9) than in Group 2b (P&#x2009;<&#x2009;.001) and Group 2a (P&#x2009;<&#x2009;.001). Optimal diagnostic cut-off for SAA concentration was 51.3&#x2009;mg/L. yielding a sensitivity of 88% (95% confidence interval: [64%; 99%]) and a specificity of 94% (95% confidence interval: [88%; 97%]). CONCLUSIONS AND CLINICAL IMPORTANCE: Measurement of SAA could be used to rule out pyelonephritis in the case of low suspicion of the disease. Increased SAA concentration is suggestive of pyelonephritis despite a lack of specificity.