The serum-ascites albumin gradient or gap (SAAG) is a calculation used in medicine to help determine the cause of ascites. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate versus exudate. The serum-ascites albumin gradient or gap (SAAG) is a calculation used in medicine to help determine the cause of ascites. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate versus exudate.