Editing Malabsorption

{{Short description|Abnormality in absorption of food nutrients across the gastrointestinal tract}}
{{cs1 config|name-list-style=vanc}}
{{Infobox medical condition (new)
| name          = Malabsorption
| synonyms      =
| image         = whipple2.jpg
| caption       = [[Whipple's disease]]: Alcian blue with apparently [[eosin]] counterstain enlarged [[Intestinal villus|villus]] with many [[macrophages]]
| pronounce     =
| field         = Gastroenterology
| symptoms      =
| complications = [[Malnutrition]]; [[anaemia]]; [[steatorrhoea]]; [[diarrhoea]]
| onset         =
| duration      =
| types         =
| causes        = [[Coeliac disease]]; [[short bowel syndrome]]; [[lactase deficiency]]; [[exocrine pancreatic insufficiency]]; [[small intestinal bacterial overgrowth]]; [[Whipple's disease]]; genetic diseases; certain medications<ref name="medline" />
| risks         =
| diagnosis     =
| differential  =
| prevention    =
| treatment     = Depends on cause
| medication    =
| prognosis     =
| frequency     =
| deaths        =
}}
'''Malabsorption''' is a state arising from abnormality in [[absorption (small intestine)|absorption]] of [[Nutrient|food nutrients]] across the [[gastrointestinal tract|gastrointestinal (GI) tract]]. Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to [[malnutrition]] and a variety of [[anemia|anaemias]].<ref name="medline">{{Cite web|title=Malabsorption Syndrome|url=https://medlineplus.gov/malabsorptionsyndromes.html|access-date=29 April 2018|publisher=MedlinePlus|language=en}}</ref>

Normally the human gastrointestinal tract digests and absorbs dietary nutrients with remarkable efficiency. A typical Western diet ingested by an adult in one day includes approximately 100 g of fat, 400 g of carbohydrate, 100 g of protein, 2 L of fluid, and the required [[sodium]], [[potassium]], [[chloride]], [[calcium]], [[vitamins]], and other elements. {{Citation needed|date=June 2018}} [[Salivary]], [[gastric]], [[intestinal]], [[hepatic]], and [[pancreatic]] secretions add an additional 7–8 L of protein-, lipid-, and electrolyte-containing fluid to intestinal contents. This massive load is reduced by the small and large intestines to less than 200 g of stool that contains less than 8 g of fat, 1–2 g of nitrogen, and less than 20&nbsp;mmol each of {{chem2|Na+}}, {{chem2|K+}}, {{chem2|Cl-}}, {{chem2|HCO3-}}, {{chem2|Ca(2+)}}, or {{chem2|Mg(2+)}}.

If there is impairment of any of the many steps involved in the complex process of nutrient digestion and absorption, intestinal ''malabsorption'' may ensue. If the abnormality involves a single step in the absorptive process, as in primary [[lactase deficiency]], or if the disease process is limited to the very proximal small intestine, then selective malabsorption of only a single nutrient may occur. However, generalized ''malabsorption'' of multiple dietary nutrients develops when the disease process is extensive, thus disturbing several digestive and absorptive processes, as occurs in [[coeliac disease]] with extensive involvement of the [[small intestine]].<ref name="medline" />

==Signs and symptoms==

===Gastrointestinal manifestations===
Depending on the nature of the disease process causing malabsorption and its extent, gastrointestinal symptoms may range from severe to subtle or may even be totally absent. [[Diarrhea]], [[weight loss]], [[flatulence]], abdominal [[bloating]], abdominal [[cramps]], and pain may be present. Although diarrhea is a common complaint, the character and frequency of stools may vary considerably ranging from over 10 watery stools per day to less than one voluminous putty-like stool, the latter causing some patients to complain of constipation. On the other hand, stool mass is invariably increased in patients with [[steatorrhea]] and generalized malabsorption above the normal with 150–200 g/day. Not only do unabsorbed nutrients contribute to stool mass but mucosal fluid and electrolyte secretion is also increased in diseases associated with mucosal inflammation such as [[coeliac disease]]. In addition, unabsorbed fatty acids, converted to hydroxy-fatty acids by colonic flora, as well as unabsorbed [[bile acid]]s both impair absorption and induce secretion of water and electrolytes by the colon adding to stool mass. Weight loss is common among patients with significant intestinal malabsorption but must be evaluated in the context of caloric intake. Some patients compensate for fecal wastage of unabsorbed nutrients by significantly increasing their oral intake. Eliciting a careful dietary history from patients with suspected malabsorption is therefore crucial. Excessive flatus and abdominal bloating may reflect excessive gas production due to fermentation of unabsorbed carbohydrate, especially among patients with a primary or secondary [[disaccharidase]] deficiency, such as [[lactose intolerance]] or [[sucrose intolerance]]. 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 [[Crohn's disease]], but it is absent in many patients with coeliac disease or postgastrectomy malabsorption.<ref name="medline" />

===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 anemia|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 [[lymphangiectasia|lymphatic obstruction]] or extensive mucosal inflammation. Dermatitis and peripheral neuropathy may be caused by malabsorption of specific vitamins or micronutrients and essential fatty acids.<ref>{{Cite journal|last=Fine|first=KD|last2=Schiller|first2=LR|date=1999|title=technical review on the evaluation and management of chronic diarrhea|journal=Gastroenterology|volume=116|issue=6|pages=1464–1486|doi=10.1016/s0016-5085(99)70513-5|pmid=10348832|s2cid=12239612}}</ref>

===Presentation===
[[File:Small-Intestine-highlighted.gif|thumb|Small intestine : major site of absorption]]
Symptoms can manifest in a variety of ways and features might give a clue to the underlying condition. Symptoms can be [[intestine|intestinal]] or extra-intestinal - the former predominates in severe malabsorption.{{citation needed|date=May 2022}}
* [[Diarrhoea]], often [[steatorrhoea]], is the most common feature.  Watery, diurnal and nocturnal, bulky, frequent stools are the clinical hallmark of overt malabsorption.  It is due to impaired water, [[carbohydrate]] and [[electrolyte]] absorption or irritation from unabsorbed [[fatty acid]]. The latter also results in [[bloating]], [[flatulence]] and abdominal discomfort.  Cramping pain usually suggests obstructive intestinal segment ''e.g.'' in [[Crohn's disease]], especially if it persists after defecation.<ref name="julio" />
* Weight loss can be significant despite increased oral intake of nutrients.<ref>health a to z{{Cite web|title=Malabsorption syndrome|url=http://www.healthatoz.com/healthatoz/Atoz/common/standard/transform.jsp?requestURI=/healthatoz/Atoz/ency/malabsorption_syndrome.jsp|url-status=dead|archive-url=https://web.archive.org/web/20070522222611/http://www.healthatoz.com/healthatoz/Atoz/common/standard/transform.jsp?requestURI=%2Fhealthatoz%2FAtoz%2Fency%2Fmalabsorption_syndrome.jsp|archive-date=2007-05-22|access-date=2007-05-10}}</ref>
* Growth retardation, failure to thrive, delayed [[puberty]] in children
* Swelling or [[oedema]] from loss of [[protein]]
* [[Anaemia]]s, commonly from [[vitamin B12|vitamin B<sub>12</sub>]], [[folic acid]] and [[iron deficiency (medicine)|iron deficiency]] presenting as fatigue and weakness, and the first of which can give rise to neuropsychiatric symptoms such as [[Paresthesia|abnormal sensations]], [[Ataxia|difficulty walking]], and decreased mental abilities.
* Muscle [[cramp]] from decreased [[vitamin D]], [[calcium]] absorption. Also lead to [[osteomalacia]] and [[osteoporosis]]
* Bleeding tendencies from [[vitamin K]] and other [[coagulation factor]] deficiencies.

==Causes==
{|
|-
|'''Due to infective agents'''{{citation needed|date=May 2022}}
* [[HIV]] related malabsorption
* Intestinal [[tuberculosis]]
* [[parasitism|Parasites]] ''e.g.'', [[diphyllobothrium]] (fish tape worm)  (B<sub>12</sub> malabsorption), [[giardiasis]] (''Giardia lamblia''), [[hookworm]] (''Ancylostoma duodenale'' [[Strongyloides stercoralis|roundworm]], and ''Necator americanus'')
* [[Traveler's diarrhea]]
* [[Tropical sprue]]
* [[Whipple's disease]]
|-
|'''Due to structural defects'''<ref>{{Cite book|last=Losowsky, M.S.|title=Malabsorption in clinical practice|publisher=Churchill Livingstone|year=1974|isbn=0-443-01007-2|location=Edinburgh}}</ref>
* [[Blind loop syndrome|Blind loops]]
* [[Fistulae]], [[Diverticulum|diverticula]] and [[strictures]]
* Infiltrative conditions such as [[amyloidosis]], [[lymphoma]], [[eosinophilic gastroenteritis]]
* Inflammatory bowel diseases, as in [[Crohn's disease]]
* [[Radiation enteritis]]
* [[Short bowel syndrome]]
* [[Systemic sclerosis]] and collagen vascular diseases
|-
|'''Due to surgical structural changes'''
* [[Weight loss surgery|Bariatric surgery (Weight loss surgery)]]
* [[Gastrectomy]]; [[Vagotomy]]
|-
|'''Due to mucosal abnormality'''
* [[Coeliac disease]]
* Cows' milk intolerance
* [[Fructose malabsorption]]
* Soya milk intolerance
|-
|'''Due to enzyme deficiencies'''
* Lactase deficiency inducing [[lactose intolerance]] (constitutional, secondary or rarely congenital)
* Intestinal disaccharidase deficiency
* Intestinal enteropeptidase deficiency
* [[Sucrose intolerance]]
|-
|'''Due to digestive failure'''
* Bile acid/[[Bile salt malabsorption]]
** [[Bacterial overgrowth]]
** [[Obstructive jaundice]]
** [[Primary bile acid diarrhea]]
** Terminal ileal disease such as Crohn's disease
* Pancreatic insufficiencies:
** [[Carcinoma of pancreas]]
** [[Chronic pancreatitis]]
** [[Cystic fibrosis]]
* [[Zollinger-Ellison syndrome]]
|-
|'''Due to other [[systemic disease]]s affecting GI tract'''
* [[Abetalipoproteinemia|Abetalipoproteinaemia]]
* [[Addison's disease]]
* [[Carcinoid syndrome]]
* [[Coeliac disease]]
* [[Common variable immunodeficiency|Common variable immunodeficiency (CVID)]]
* Fiber Deficiency
* [[Pernicious anemia]] (lack of [[intrinsic factor]], B<sub>12</sub> malabsorption)
* [[Hypothyroidism]] and [[hyperthyroidism]]
* [[Diabetes mellitus]]
* [[mast cell activation syndrome|Mast cell activation syndrome (MCAS)]]<ref name="PMID27012973">{{cite journal|vauthors=Afrin LB, Butterfield JH, Raithel M, Molderings GJ|title=Often seen, rarely recognized: mast cell activation disease--a guide to diagnosis and therapeutic options|journal=The American Journal of the Medical Science|volume=48|issue=3|date=2016|pages=190-201|DOI=10.3109/07853890.2016.1161231|PMID=27012973|url=|doi-access=free}}</ref>
* [[Hyperparathyroidism]] and [[Hypoparathyroidism]]
* Malnutrition
|-
|'''Other Possible Causes'''
* Chronic Proton Pump Inhibitor Use<ref>{{Cite journal|last=Heidelbaugh|first=Joel J.|date=June 2013|title=Proton pump inhibitors and risk of vitamin and mineral deficiency: evidence and clinical implications|journal=Therapeutic Advances in Drug Safety|volume=4|issue=3|pages=125–133|doi=10.1177/2042098613482484|issn=2042-0986|pmc=4110863|pmid=25083257}}</ref>
|}

==Pathophysiology==
The main purpose of the [[gastrointestinal tract]] is to [[digestion|digest]] and [[absorption (small intestine)|absorb]] nutrients ([[fat]], [[carbohydrate]], [[protein]], micronutrients ([[vitamin]]s and [[dietary mineral|trace minerals]]), water, and [[electrolytes]]. [[Digestion]] involves both mechanical and [[enzyme|enzymatic]] breakdown of food. '''Mechanical processes''' include chewing, gastric churning, and the to-and-fro mixing in the [[small intestine]]. '''Enzymatic hydrolysis''' is initiated by intraluminal processes requiring gastric, pancreatic, and biliary secretions. The final products of digestion are absorbed through the [[Intestinal epithelium|intestinal epithelial]] cells.{{citation needed|date=November 2017}}

Malabsorption constitutes the pathological interference with the normal physiological sequence of [[digestion]] (intraluminal process), absorption (mucosal process) and transport (postmucosal events) of nutrients.<ref name="julio">{{Cite journal|last=Bai J|year=1998|title=Malabsorption syndromes|journal=Digestion|volume=59|issue=5|pages=530–46|doi=10.1159/000007529|pmid=9705537|s2cid=46786949}}</ref>

[[Intestine|Intestinal]] malabsorption can be due to:<ref>{{Cite journal|vauthors=Walker-Smith J, Barnard J, Bhutta Z, Heubi J, Reeves Z, Schmitz J|year=2002|title=Chronic diarrhea and malabsorption (including short gut syndrome): Working Group Report of the First World Congress of Pediatric Gastroenterology, Hepatology, and Nutrition|journal=J. Pediatr. Gastroenterol. Nutr.|volume=35|issue=Suppl 2|pages=S98–105|doi=10.1097/00005176-200208002-00006|pmid=12192177|s2cid=10373517|doi-access=free}}</ref>
* [[Congenital disorder|Congenital]] or acquired reduction in absorptive surface
* Defects of [[ion]] transport
* Defects of specific [[hydrolysis]]
* Impaired [[enterohepatic circulation]]
* Mucosal damage ([[enteropathy]])
* [[Pancreas|Pancreatic]] insufficiency

==Diagnosis==
There is no single, specific test for malabsorption. As for most medical conditions, investigation is guided by [[symptom]]s and signs. A range of different conditions can produce malabsorption and it is necessary to look for each of these specifically. Many tests have been advocated, and some, such as tests for pancreatic function are complex, vary between centers and have not been widely adopted. However, better tests have become available with greater ease of use, better sensitivity and specificity for the causative conditions. Tests are also needed to detect the systemic effects of deficiency of the malabsorbed nutrients (such as anaemia with vitamin B12 malabsorption).{{citation needed|date=November 2017}}

===Classification===
Some{{who|date=July 2018}} prefer to classify malabsorption clinically into three basic categories:<ref>Gasbarrini G,  Frisono M: Critical evaluation of malabsorption tests; in {{Cite book|title=Problems and Controversies in Gastroenterology|vauthors=Dobrilla G, Bertaccini G|publisher=Raven Pr|year=1986|isbn=88-85037-75-5|veditors=Langman G|location=New York|pages=123–130}}</ref>
# '''selective''', as seen in [[lactose malabsorption]].
# '''partial''', as observed in [[abetalipoproteinaemia]].
# '''total''', as in exceptional cases of [[coeliac disease]].<ref name="Newnham2017">{{Cite journal|last=Newnham ED|year=2017|title=Coeliac disease in the 21st century: paradigm shifts in the modern age.|journal=J Gastroenterol Hepatol|type=Review|volume=32|issue=Suppl 1|pages=82–85|doi=10.1111/jgh.13704|pmid=28244672|doi-access=free}}</ref>

===Blood tests===
* Routine [[blood test]]s may reveal [[anaemia]], high [[C-reactive protein|CRP]] or low [[serum albumin|albumin]]; which shows a high correlation for the presence of an organic disease.<ref>{{Cite journal|vauthors=Bertomeu A, Ros E, Barragán V, Sachje L, Navarro S|year=1991|title=Chronic diarrhea with normal stool and colonic examinations: organic or functional?|journal=J. Clin. Gastroenterol.|volume=13|issue=5|pages=531–6|doi=10.1097/00004836-199110000-00011|pmid=1744388}}</ref><ref>{{Cite journal|vauthors=Read N, Krejs G, Read M, Santa Ana C, Morawski S, Fordtran J|year=1980|title=Chronic diarrhea of unknown origin|journal=Gastroenterology|volume=78|issue=2|pages=264–71|doi=10.1016/0016-5085(80)90575-2|pmid=7350049|doi-access=free}}</ref> In this setting, [[microcytic anemia|microcytic anaemia]] usually implies iron deficiency and [[macrocytosis]] can be caused by impaired [[folic acid]] or [[vitamin B12|B12]] absorption or both. Low cholesterol or triglyceride may give a clue toward fat malabsorption.<ref name="Thomas" /> Low calcium and phosphate may give a clue toward [[osteomalacia]] from low vitamin D.<ref name="Thomas" />
* 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.<ref>{{Cite journal|last=Sankararaman|first=Senthilkumar|last2=Hendrix|first2=Sara J.|last3=Schindler|first3=Terri|date=October 2022|title=Update on the management of vitamins and minerals in cystic fibrosis|url=https://aspenjournals.onlinelibrary.wiley.com/doi/10.1002/ncp.10899|journal=Nutrition in Clinical Practice|language=en|volume=37|issue=5|pages=1074–1087|doi=10.1002/ncp.10899|issn=0884-5336|pmc=9544449}}</ref>
* 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]]).<ref>{{Cite journal|date=2017-09-01|title=Tests for Serum Transglutaminase and Endomysial Antibodies Do Not Detect Most Patients With Celiac Disease and Persistent Villous Atrophy on Gluten-free Diets: a Meta-analysis|url=https://linkinghub.elsevier.com/retrieve/pii/S001650851735624X|journal=Gastroenterology|language=en|volume=153|issue=3|pages=689–701.e1|doi=10.1053/j.gastro.2017.05.015|pmc=5738024}}</ref>

===Stool studies===
* Microscopy is particularly useful in diarrhoea, may show protozoa like [[Giardia]], ova, cyst and other infective agents.
* [[Fecal fat|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<ref name="Thomas">{{Cite journal|vauthors=Thomas P, Forbes A, Green J, Howdle P, Long R, Playford R, Sheridan M, Stevens R, Valori R, Walters J, Addison G, Hill P, Brydon G|year=2003|title=Guidelines for the investigation of chronic diarrhoea, 2nd edition|journal=Gut|volume=52 Suppl 5|issue=90005|pages=v1–15|doi=10.1136/gut.52.suppl_5.v1|pmc=1867765|pmid=12801941}}</ref>

===Radiological studies===
* [[Barium follow through]] is useful in delineating [[small intestine|small intestinal]] [[anatomy]]. [[Barium enema]] may be undertaken to see [[Colon (anatomy)|colon]]ic or ileal [[lesion]]s.
* 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 [[Endoscopic retrograde cholangiopancreatography|ERCP]].

===Interventional studies===
[[File:Coeliac path.jpg|thumb|right|Biopsy of [[small bowel]] showing [[coeliac disease]] manifested by blunting of [[Intestinal villus|villi]], crypt [[hyperplasia]], and [[lymphocyte]] infiltration of crypts.]]
* [[Esophagogastroduodenoscopy|OGD]] to detect [[duodenum|duodenal]] pathology and obtain D2 [[biopsy]] (for [[coeliac disease]], [[tropical sprue]], [[Whipple's disease]], abetalipoproteinaemia etc.)
* [[Enteroscopy]] for enteropathy and [[jejunum|jejunal]] aspirate and [[cell culture|culture]] for [[bacteria]]l overgrowth
* [[Capsule Endoscopy]] is able to visualise the whole [[small intestine]] and is occasionally useful.
* [[Colonoscopy]] is necessary in colonic and ileal disease.
* [[Endoscopic retrograde cholangiopancreatography|ERCP]] will show pancreatic and biliary structural abnormalities.

===Other investigations===
* <sup>75</sup>[[SeHCAT]] test to diagnose [[bile acid malabsorption]] in ileal disease or [[primary bile acid diarrhea]].
* Glucose hydrogen breath test for [[bacterial overgrowth]]
* [[Lactose]] hydrogen breath test for [[lactose intolerance]]
* Sugar probes or <sup>51</sup>Cr-[[EDTA]] to determine [[intestinal permeability]].<ref name="julio" />

===Obsolete tests no longer used clinically===
* [[D-xylose]] absorption test for mucosal disease or bacterial overgrowth. Normal in pancreatic insufficiency.
* [[Bile salt]] breath test (<sup>14</sup>C-glycocholate) to determine [[bile salt]] malabsorption.
* [[Schilling test]] to establish cause of B<sub>12</sub> deficiency.

==Management==
Treatment is directed largely towards management of underlying cause:<ref name="medline" />
* Replacement of nutrients, [[electrolyte]]s and fluid may be necessary. In severe deficiency, hospital admission may be required for nutritional support and detailed advice from [[dietitian]]s. Use of enteral nutrition by naso-gastric or other [[feeding tube]]s may be able to provide sufficient nutritional supplementation. Tube placement may also be done by [[percutaneous endoscopic gastrostomy]], or surgical [[jejunostomy]]. In patients whose intestinal absorptive surface is severely limited from disease or surgery, long term [[total parenteral nutrition]] may be needed.
* Pancreatic [[enzymes]] are supplemented orally in pancreatic insufficiency.
* Dietary modification is important in some conditions:
** Gluten-free diet in [[coeliac disease]].
** Lactose avoidance in [[lactose intolerance]].
* [[Antibiotic]] therapy to treat Small Bowel [[Bacterial overgrowth]].
* [[Cholestyramine]] or other [[bile acid sequestrants]] will help with reducing diarrhoea in [[bile acid malabsorption]].

==See also==
* [[Fructose malabsorption]]
* [[Protein losing enteropathy]]

==References==
{{Reflist}}

== External links ==
{{Medical resources
|  DiseasesDB     = 7698
|  ICD10          = ({{ICD10|K|90||k|90}})
|  ICD9           = {{ICD9|579}}
|  ICDO           =
|  OMIM           =
|  MedlinePlus    = 000299
|  eMedicineSubj  = med
|  eMedicineTopic = 1384
|  MeshID         = D008286
}}

{{Gastroenterology}}
{{Authority control}}

[[Category:Gastrointestinal tract disorders]]
[[Category:Steatorrhea-related diseases]]
[[Category:Diarrhea]]