Malabsorption of dietary nutrients and excessive fluid secretion by inflamed small intestine also contribute to abdominal distention and bloating. Prevalence, severity, and character of abdominal pain vary considerably among the various disease processes associated with intestinal malabsorption. For example, pain is common in patients with chronic pancreatitis or pancreatic cancer and Crohns disease, but it is absent in many patients with coeliac disease or postgastrectomy malabsorption. Extraintestinal manifestations
Substantial numbers of patients with intestinal malabsorption present initially with symptoms or laboratory abnormalities that point to other organ systems in the absence of or overshadowing symptoms referable to the gastrointestinal tract. For example, there is increasing epidemiologic evidence that more patients with coeliac disease present with anemia and osteopenia in the absence of significant classic gastrointestinal symptoms. Microcytic, macrocytic, or dimorphic anemia may reflect impaired iron, folate, or vitamin B12 absorption. Purpura, subconjunctival hemorrhage, or even frank bleeding may reflect hypoprothrombinemia secondary to vitamin K malabsorption. Osteopenia is common, especially in the presence of steatorrhea. Impaired calcium and vitamin D absorption and chelation of calcium by unabsorbed fatty acids resulting in fecal loss of calcium may all contribute. If calcium deficiency is prolonged, secondary hyperparathyroidism may develop. Prolonged malnutrition may induce amenorrhea, infertility, and impotence. Edema and even ascites may reflect hypoproteinemia associated with protein losing enteropathy caused by lymphatic obstruction or extensive mucosal inflammation. Dermatitis and peripheral neuropathy may be caused by malabsorption of specific vitamins or micronutrients and essential fatty acids.
Low calcium and phosphate may give a clue toward osteomalacia from low vitamin D.
Specific vitamins like vitamin D or micronutrient like zinc levels can be checked. Fat soluble vitamins (A, D, E and K) are affected in fat malabsorption. Prolonged prothrombin time can be caused by vitamin K deficiency. Serological studies. Specific tests are carried out to determine the underlying cause.IgA Anti-transglutaminase antibodies or IgA Anti-endomysial antibodies for Coeliac disease (gluten sensitive enteropathy). Stool studies
Microscopy is particularly useful in diarrhoea, may show protozoa like Giardia, ova, cyst and other infective agents. Fecal fat study to diagnose steatorrhoea is rarely performed nowadays. Low fecal pancreatic elastase is indicative of pancreatic insufficiency. Chymotrypsin and pancreolauryl can be assessed as well

Radiological studies
Barium follow through is useful in delineating small intestinal anatomy. Barium enema may be undertaken to see colonic or ileal lesions. CT abdomen is useful in ruling out structural abnormality,  done in pancreatic protocol when visualising pancreas. Magnetic resonance cholangiopancreatography (MRCP) to complement or as an alternative to ERCP. Interventional studies
OGD to detect duodenal pathology and obtain D2 biopsy (for coeliac disease, tropical sprue, Whipples disease, abetalipoproteinaemia etc.) Enteroscopy for enteropathy and jejunal aspirate and culture for bacterial overgrowth
Capsule Endoscopy is able to visualise the whole small intestine and is occasionally useful. Colonoscopy is necessary in colonic and ileal disease. ERCP will show pancreatic and biliary structural abnormalities. Other investigations
75SeHCAT test to diagnose bile acid malabsorption in ileal disease or primary bile acid diarrhea.