What is the step-by-step diagnostic approach to the acute vomiting dog to differentiate GI from systemic causes?

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The acute vomiting dog requires a tiered diagnostic approach that first separates life-threatening surgical emergencies from medical causes, then stratifies medical differentials using targeted testing. Physical examination is the critical first step. Tachycardia (reference range 80–120 beats/min), dehydration, tacky mucous membranes, abdominal distension, and pain on palpation are the cardinal signs that flag a surgical or hemodynamically unstable patient requiring immediate intervention before further workup.6 Sudden collapse combined with acute vomiting raises the urgency further — hemorrhagic peritoneal effusion, marked thrombocytopenia, and markedly elevated liver enzymes are findings that can accompany acute hemoabdomen in young large-breed dogs.3 Baseline clinicopathologic testing — CBC, serum biochemical profile, and urinalysis — is the standard first diagnostic tier. This combination identifies systemic contributors (hepatobiliary disease, urinary obstruction, metabolic derangements) and flags hematologic abnormalities such as anemia or thrombocytopenia that redirect the differential.14 Blood gas analysis is appropriate when cardiovascular compromise is present; in one acute abdomen presentation, serum biochemistry and blood gas results were within reference limits despite significant tachycardia and dehydration, illustrating that normal chemistry does not exclude a surgical lesion.6 Pancreas-specific lipase measurement is indicated when acute pancreatitis is on the differential, but a positive result does not confirm it as the sole diagnosis. Gastrointestinal foreign body obstruction (GIFBO) is not associated with abnormal point-of-care pancreas-specific lipase results, so an elevated lipase in a vomiting dog should not be used to exclude a mechanical obstruction.1 Pancreatic lipase immunoreactivity is included in the standard diagnostic panel for acute vomiting at tertiary care facilities alongside CBC, biochemical profile, and urinalysis.4 Abdominal imag