Comparison of the diagnostic predictability of serum amyloid A, white blood cell count and immunoglobulin G tests as indicators of early‐onset, acute‐phase morbidities in newborn foals

Abstract

SummaryBackgroundAcute‐phase proteins (APPs) have diagnostic value as nonspecific, early indicators of inflammation and infectious disease.ObjectivesTo assess the ability of serum amyloid A (SAA) testing to distinguish between healthy and nonhealthy newborn foals, and to compare the diagnostic predictability of SAA with white blood cell (WBC) counts and serum immunoglobulin G (IgG) concentration.Study designThree‐year prospective clinical evaluation and diagnostic sample collection from newborn foals.MethodsFollowing an examination, a blood sample was obtained from each foal and tested for SAA and IgG concentrations, complete blood count (CBC) and standard biochemistry values. Foals were categorised as healthy or nonhealthy based on the clinical examination. The presence of clinical signs of infectious origin or certain noninfectious morbidities with a pro‐inflammatory component was sufficient for a nonhealthy designation. Serum amyloid A, IgG and WBC test results were determined and compared for healthy and nonhealthy foals.ResultsA total of 24 (13.7%) foals were diagnosed as clinically sick and 151 (86.3%) as normal based on physical examinations performed within 24 h after parturition. Mean SAA values were 27.7 ± 129.0 mg/L and 247.2 ± 454.8 mg/L for healthy and nonhealthy foals, respectively, a significant (p < 0.05) difference indicating that elevated SAA values are associated with a nonhealthy diagnosis. Using a positive threshold of 100 mg/L, the SAA test had a positive predictive value (PPV) of 55.6% and IgG had the lowest PPV (16.7%) followed by WBC count (23.3%).Main limitationsA larger number of clinically nonhealthy foals with SAA levels >100 would have given the study greater statistical power.ConclusionsEquine practitioners can consider SAA testing to be a reliable newborn examination diagnostic tool for detecting early‐onset, acute‐phase infection or noninfectious morbidities with an inflammatory component.