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Introduction The Chicago Classification v4.0 recommends provocative manoeuvres such as rapid drink Challenge (RDC) during oesophageal high-resolution manometry (HRM) to characterize oesophagogastric junction (OGJ) outflow obstruction. Solid test meal (STM) is optional and reserved for inconclusive cases. EndoFLIP provides complementary assessment of OGJ distensibility using the Dallas Consensus criteria. However, the relationship between HRM provocative manoeuvres and reduced OGJ opening (REO) on EndoFLIP remains poorly characterized. We hypothesized that STM would better predict REO than RDC in patients with achalasia spectrum disorders.Methods Prospective pilot study of consecutive patients with dysphagia referred for motility evaluation at two tertiary London centres. All patients underwent HRM (Medtronic system) with provocative manoeuvres (wet swallows, RDC, STM) and EndoFLIP P (Medtronic, 16 cm balloon EF-322N or 8 cm balloon, EF-325). HRM were classified per Chicago Classification v4.0; OGJ opening on EndoFLIP was classified per Dallas Consensus using the same classification criteria for both catheter types. REO defined as EGJ-distensibility index (DI) <2.0 mm 2/mmHg and max EGJ diameter <12 mm. Non-relaxing LES on STM: ≥2 swallows with IRP >25 mmHg; non-relaxing LES on RDC: IRP >8 mmHg. Associations were analyzed using Fisher’s exact test, and diagnostic performance compared using McNemar’s exact test.Results Fifty patients were enrolled (mean age 51.1±15.1 years, 60% female). HRM diagnoses were achalasia 70%, esophagogastric junction outflow obstruction 12%, other 18%; 46% were previously treated patients (Botox, pneumatic dilatation, peroral endoscopic myotomy, or Heller’s myotomy). REO was present in 16 patients (32%). STM significantly predicted REO (OR=13.1, p=0.007; figure 1A) with a 40% absolute risk difference (46.7% vs 6.2%). RDC showed only a non-significant trend (OR=4.2, p=0.24; figure 1B). STM demonstrated numerically higher specificity (48% vs 28%, p=0.125) and accuracy (63% vs 46%, p=0.063) compared to RDC. In previously treated patients (n=23), REO occurred exclusively in those with abnormal STM (50% vs 0%, p=0.010).Conclusions STM significantly predicts REO on FLIP Panometry (OR=13.1, p=0.007), while RDC does not reach statistical significance. This association is particularly strong in previously treated patients. STM may represent a more physiologically relevant provocative manoeuvre for identifying mechanical EGJ obstruction warranting intervention. These pilot data inform the design of a definitive study to evaluate STM’s role in clinical decision-making for achalasia spectrum disorders.Abstract P139 Figure 1