CEACAM5 and cyst: Several other studies have been published about the optimal level of CEA in cyst fluid to identify mucinous cysts, which is in the range of 30 to 480 ng/mL.19-21 An older study using a cutoff point of 400 ng/mL for CEA reported a sensitivity of 57% and a specificity of 100% in differentiating between lesions.22