Percent recovery

It's an excerpt from this page: https://www.gdx.net/core/interpretive-guides/Intestinal-Permeability-Interp-Guide.pdf

What does this test involve?

Following an overnight fast, the patient collects a urine sample and then drinks a premeasured challenge drink containing lactulose and mannitol (two non metabolized sugar molecules). A second urine sample is later drawn from a six-hour collection. The report includes lactulose percent recovery, mannitol percent recovery and a lactulose/mannitol ratio.

--- I understand that "lactulose percent recovery" and "mannitol percent recovery" mean how much lactulose and mannitol are detected in the urine samples?