Construct the differential diagnosis of malabsorption for various patients.

Explanation:

In general proximal small bowel malabsoprtion syndromes present with chronic diarrhea and decreased Fe, folate, Ca, Mg.

Lactose intolerance is very common.

Examples include bacterial overgrowth where B12 is low but Folate level is high, tropical and non-tropical sprue, Whipple's disease where one sees PAS positive material within cells of the small bowel.

GI lymphoma where one sees protein loss in the stool but diagnosis will be made by doing a barium small bowel study.

Distal (Ileal) small bowel disease  typically presents with oxalate kidney stones, steattorhea, weight loss, fat soluble vitamin deficiencies. Examples include Crohn's disease and ileal resection.