The most sensitive diagnostic evaluation for achalasia cardia is:

Achalasia is diagnosed by barium swallow x-ray, esophageal manometry and rarely with endosc (To exclude pseudoachalasia). The diagnostic criteria for achalasia with esophageal manometry are impaired LES relaxation and absent peristalsis. High-resolution manometry identifies early disease before esophageal dilatation and food retention, it is the most sensitive diagnostic test. Ref: Harrison, Edition-18, Page-2431