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BackgroundIt has been reported that qualitative ultrasound assessment performed in the semi‐upright position had high sensitivity to detect gastric fluid volume >1.5 mL.kg−1. Nevertheless, the diagnostic accuracy of qualitative assessment for the diagnosis of empty stomach (fluid volume <0.8 mL.kg−1) has not been assessed. We aimed to assess the diagnostic accuracy of simple qualitative ultrasound assessment with and without head‐of‐bed elevation to 45° for the diagnosis of an empty stomach. We also aimed to determine the diagnostic accuracy of a composite ultrasound scale and clinical algorithm.MethodsWe performed a supplementary analysis of a prospective observer‐blind randomized crossover trial in which adult fasting volunteers attended two distinct sessions, with the head‐of‐bed angled either at 0° or 45°, in a randomized order. Three tests were performed within each session, each corresponding to a different (either 0, 50, 100, 150 or 200 mL) and randomized volume of water; the same volumes were ingested in both sessions, in a randomized order. Ultrasounds were performed 3 min after water ingestion, blindly to the volume ingested.ResultsWe included 20 volunteers in whom 120 measurements were analyzed. The sensitivity and specificity of the qualitative assessment in the semirecumbent position were 93% (95% CI: 68–100) and 89% (95% CI: 76–96), respectively. The composite scale and clinical algorithm did not have better diagnostic accuracy than the qualitative assessment performed with head‐of‐bed elevation. Without head‐of‐bed elevation, the clinical algorithm had significantly higher specificity (98% [95% CI: 88–100]) than qualitative assessment (67% [95% CI: 51–80]; p < 0.05).ConclusionThese results suggest that qualitative assessment in the semirecumbent position had high diagnostic accuracy for the diagnosis of fluid volume <0.8 mL.kg−1; this method can be used in clinical practice for reliable diagnosis of empty stomach.