Lung ultrasonography used as a diagnostic test for respiratory disease diagnosis in calves: systematic review and meta-analysis using a Bayesian latent-class modelling approach.

Bovine respiratory disease complex is a common disease which commonly affects calves in the form of bronchopneumonia.There is currently no affordable perfectly accurate reference standard test and the routine diagnosis is commonly based on clinical signs assessment or other ancillary tests.Lung ultrasonography (LUS) has emerged as a practical calf-side test that can be done routinely.However, information on this diagnostic test's accuracy is limited especially because no test reaches the accuracy of a gold-standard comparator test.The objective of this systematic review and meta-analysis was to determine the accuracy of LUS while adjusting for imperfect accuracy of available reference standard (RS) tests, including clinical scoring systems, using a Bayesian latent class meta-analysis approach.A structured literature search was performed and from 875 studies screened, 26 studies reported at least one 2 2 table with cross classification of LUS (positive vs negative) calves and RS test (positive vs negative).The RS test included were Wisconsin Clinical Respiratory Score (WCRS, n = 16), California Clinical Respiratory Score (CaCRS, n = 4), other clinical signs combinations (n = 5), clinical score combined with bronchial lavage results (n = 1), thoracic radiograph (n = 1), expert panel diagnosis (n = 1) and necropsy (n = 1).Various LUS thresholds for test positivity were reported but 2 thresholds of maximal consolidation depth 1cm or 3cm, were most commonly reported in 12 and 8 studies, respectively.The QUADAS-2 assessment for risk of bias and applicability revealed that besides limitations associated with an imperfect RS test, it was difficult to know if LUS results were interpreted without the knowledge of RS test results.A Bayesian latent class meta-analysis accounting for the imperfect accuracy of WCRS was performed for both positivity thresholds.Eight studies were available for LUS 1cm.The median pooled sensitivity (95% BCI) and specificity were 68.4% (51.7-87.4%)and 91.2% (78.5-99.4%)respectively.Five studies were available for LUS 3cm.The median pooled sensitivity and specificity were 58.2% (38.4-80%) and 95.8% (86.7-99.4%)respectively.The LUS appeared as a moderately sensitive test with a relatively high specificity.The models revealed heterogeneity that could not be further investigated due to the low number of available studies.This is the first reported meta-analysis to determine LUS accuracy accounting for the RS test uncertainty.This study helps to identify the gaps of knowledge and reporting issues such as standardization of LUS scanning protocol, reporting maximal consolidation in a continuous way as well as providing raw data sets to continue gathering information on LUS accuracy for the diagnosis of calf respiratory disease.