Embodiments relate to guiding medical care based on detected gastric function. For example, gastric acid stimulant or suppressant is administered, and then a change in the gastric juice H+ concentration is measured. This change is compared to a guidance H+ concentration differential indicative of relatively healthy gastric function. Medical care is guided based on a relatively healthy gastric function if the measured H+ concentration differential is equal to or exceeds the guidance H+ concentration differential, while medical care is guided based on a relatively unhealthy gastric function if the measured H+ concentration differential is less than the guidance H+ concentration differential. Disclosed embodiments implementing this procedure include, but are not limited to, methods, apparatus, processors, computer programs, and computer-readable mediums.