Acute diarrhea laboratory findings: Difference between revisions

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__NOTOC__
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{{Acute diarrhea}}
{{Acute diarrhea}}
{{CMG}}; {{AE}}  
{{CMG}}; {{AE}}{{Cherry}}


==Overview==
==Overview==
An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].


OR
Laboratory investigations performed in the evaluation of patients with acute diarrhea include spot [[Stool examination|stool analysis]], detection of [[occult blood]], [[white blood cells]], [[stool culture]], quantitative [[Stool examination|stool analysis]], fecal weight, stool osmotic gap, [[Fecal pH test|fecal pH]], [[Fecal fat|fecal fat concentration]] and analysis for [[Laxative|laxative abuse]]. According to the ACG guidelines, [[stool culture]] is done only in cases where the patient is at high risk of spreading the disease to others. [[Stool examination|Stool diagnostic studies]] are performed when symptoms last for >7 days, patient has [[dysentery]] or moderate-to-severe diarrhea and to determine [[etiology]] to enable directed [[pathogen]]-specific therapy. [[Antibiotic sensitivity|Antibiotic sensitivity testing]] for management of acute diarrhea is not advised.  
 
Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].
 
OR
 
[Test] is usually normal among patients with [disease name].
 
OR
 
Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].
 
OR
 
There are no diagnostic laboratory findings associated with [disease name].


==Laboratory Findings==
==Laboratory Findings==
Laboratory investigations performed in the workup of patients with acute diarrhea include [[Complete blood count]] ([[CBC]]), [[glucose]] levels, [[white blood cells]] ([[WBC]]) detection, urine analysis, [[calcium]] levels, [[Thyroid stimulating hormone]] ([[TSH]]) levels, [[Liver function tests]] ([[LFT]]s), [[Blood urea nitrogen]] ([[BUN]]) / [[creatinine]] levels, [[Hepatitis]] serologies and stool examination.
Laboratory investigations performed in the workup of patients with acute diarrhea include [[complete blood count]], [[glucose]] levels, [[white blood cells]] ([[WBC]]) detection, urine analysis, [[calcium]] levels, [[Thyroid stimulating hormone]] ([[TSH]]) levels, complete metabolic panel and [[stool examination]].
* Stool examination includes the following:
* [[Stool examination]] includes the following:
** Stool culture
** [[Stool culture]]
** Stool [[electrolyte]]s
** Stool [[electrolyte]]s
** Stool osmolality
** Stool osmolality
** Ova and parasites
** Ova and parasites
** Fecal [[lactoferrin]]
** [[Lactoferrin|Fecal lactoferrin]]
** Fecal [[leukocyte]]s
** [[White blood cells|Fecal leukocytes]]
** Test for ''[[C. difficile]]''
** Test for ''[[C. difficile]]''
* According to the ACG guidelines, the following points should be kept in mind in the diagnostic evaluation of acute diarrhea patients:
** [[Stool culture]] is done only in cases where the patient is at high risk of spreading the disease to others.
** Stool diagnostic studies are performed in the following cases:
*** Symptoms lasting >7 days
*** [[Dysentery]]
*** Moderate-to-severe diarrhea
*** Determination of [[etiology]] to enable directed [[pathogen]]-specific therapy
** [[Antibiotic sensitivity|Antibiotic sensitivity testing]] for management of acute diarrhea is not advised.
===Laboratory Evaluation of Acute Diarrhea===
===Laboratory Evaluation of Acute Diarrhea===


====Spot Stool Analysis====
====Spot Stool Analysis====
* Stool spot analysis is preferred over 24 hour stool collection as it is less cumbersome.
* [[Human feces|Stool]] spot analysis is preferred over 24 hour [[Human feces|stool]] collection as it is less cumbersome.


=====Occult Blood=====
=====Occult Blood=====
* A positive test result suggests the presence of [[inflammatory bowel disease]] and acute causes of bloody diarrhea.<ref name="pmid24319453">{{cite journal| author=Viana Freitas BR, Kibune Nagasako C, Pavan CR, Silva Lorena SL, Guerrazzi F, Saddy Rodrigues Coy C et al.| title=Immunochemical fecal occult blood test for detection of advanced colonic adenomas and colorectal cancer: comparison with colonoscopy results. | journal=Gastroenterol Res Pract | year= 2013 | volume= 2013 | issue=  | pages= 384561 | pmid=24319453 | doi=10.1155/2013/384561 | pmc=PMC3844264 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24319453  }} </ref>  
* A positive test result suggests the presence of [[inflammatory bowel disease]] and acute causes of [[Dysentery|bloody diarrhea]].<ref name="pmid24319453">{{cite journal| author=Viana Freitas BR, Kibune Nagasako C, Pavan CR, Silva Lorena SL, Guerrazzi F, Saddy Rodrigues Coy C et al.| title=Immunochemical fecal occult blood test for detection of advanced colonic adenomas and colorectal cancer: comparison with colonoscopy results. | journal=Gastroenterol Res Pract | year= 2013 | volume= 2013 | issue=  | pages= 384561 | pmid=24319453 | doi=10.1155/2013/384561 | pmc=PMC3844264 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24319453  }} </ref>  
* Fecal occult blood positivity may also be associated with diarrhea due to idiopathic secretory diarrhea, laxative abuse, and [[microscopic colitis]].<ref name="pmid8602182">{{cite journal| author=Fine KD| title=The prevalence of occult gastrointestinal bleeding in celiac sprue. | journal=N Engl J Med | year= 1996 | volume= 334 | issue= 18 | pages= 1163-7 | pmid=8602182 | doi=10.1056/NEJM199605023341804 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8602182  }} </ref>
* [[Fecal occult blood]] positivity may also be associated with diarrhea due to idiopathic secretory diarrhea, [[Laxative|laxative abuse]], and [[microscopic colitis]].<ref name="pmid8602182">{{cite journal| author=Fine KD| title=The prevalence of occult gastrointestinal bleeding in celiac sprue. | journal=N Engl J Med | year= 1996 | volume= 334 | issue= 18 | pages= 1163-7 | pmid=8602182 | doi=10.1056/NEJM199605023341804 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8602182  }} </ref>


=====White Blood Cells=====
=====White Blood Cells=====
* Wright's staining and microscopy is the standard method for the detection of white blood cells (WBCs) present in stool.  
* Wright's staining and microscopy is the standard method for the detection of [[White blood cells|white blood cells (WBCs)]] present in [[Human feces|stool]].  
* Neutrophils in the stool present in patients having acute infectious diarrhea may be detected by latex agglutination test.<ref name="pmid12818275">{{cite journal| author=Kane SV, Sandborn WJ, Rufo PA, Zholudev A, Boone J, Lyerly D et al.| title=Fecal lactoferrin is a sensitive and specific marker in identifying intestinal inflammation. | journal=Am J Gastroenterol | year= 2003 | volume= 98 | issue= 6 | pages= 1309-14 | pmid=12818275 | doi=10.1111/j.1572-0241.2003.07458.x | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12818275  }} </ref>  
* [[Neutrophil|Neutrophils]] in the [[Human feces|stool]] present in patients having acute infectious diarrhea may be detected by [[Latex fixation test|latex agglutination test]].<ref name="pmid12818275">{{cite journal| author=Kane SV, Sandborn WJ, Rufo PA, Zholudev A, Boone J, Lyerly D et al.| title=Fecal lactoferrin is a sensitive and specific marker in identifying intestinal inflammation. | journal=Am J Gastroenterol | year= 2003 | volume= 98 | issue= 6 | pages= 1309-14 | pmid=12818275 | doi=10.1111/j.1572-0241.2003.07458.x | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12818275  }} </ref>  
=====Stool Culture=====
=====Stool Culture=====
* In immunocompetent patients with acute diarrhea, stool culture is not routinely performed.
* In [[Immunocompetence|immunocompetent]] patients with acute diarrhea, [[stool culture]] is not routinely performed.
* If the patient has a history of swimming in streams or ponds and consuming untreated water from wells, stool culture may be performed to evaluate the patient for [[Aeromonas]] or Pleisomonas species.
* If the patient has a history of swimming in streams or ponds and consuming untreated water from wells, stool culture may be performed to evaluate the patient for [[Aeromonas]] or [[Plesiomonas shigelloides|Plesiomonas]] species.
* In immunocompromised patients, stool culture is included as a part of routine investigations to rule out infection due to bacteria such as Samonella, Campylobacter, protozoa and fungi.<ref name="pmid17277989">{{cite journal| author=Friedman M, Ramsay DB, Borum ML| title=An unusual case report of small bowel Candida overgrowth as a cause of diarrhea and review of the literature. | journal=Dig Dis Sci | year= 2007 | volume= 52 | issue= 3 | pages= 679-80 | pmid=17277989 | doi=10.1007/s10620-006-9604-4 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17277989  }} </ref>
* In [[Immunodeficiency|immunocompromised]] patients, [[stool culture]] is included as a part of routine investigations to rule out [[infection]] due to [[bacteria]] such as [[Salmonella]], [[Campylobacter]], [[protozoa]] and [[Fungus|fungi]].<ref name="pmid17277989">{{cite journal| author=Friedman M, Ramsay DB, Borum ML| title=An unusual case report of small bowel Candida overgrowth as a cause of diarrhea and review of the literature. | journal=Dig Dis Sci | year= 2007 | volume= 52 | issue= 3 | pages= 679-80 | pmid=17277989 | doi=10.1007/s10620-006-9604-4 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17277989  }} </ref>


* Protozoa may detected by the use of fecal enzyme-linked immunosorbent assay ([[ELISA]]).<ref name="pmid8863034">{{cite journal| author=Koontz F, Weinstock JV| title=The approach to stool examination for parasites. | journal=Gastroenterol Clin North Am | year= 1996 | volume= 25 | issue= 3 | pages= 435-49 | pmid=8863034 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8863034  }} </ref>
* [[Protozoa]] may detected by the use of [[Feces|fecal]] [[Enzyme linked immunosorbent assay (ELISA)|enzyme-linked immunosorbent assay]] ([[ELISA]]).<ref name="pmid8863034">{{cite journal| author=Koontz F, Weinstock JV| title=The approach to stool examination for parasites. | journal=Gastroenterol Clin North Am | year= 1996 | volume= 25 | issue= 3 | pages= 435-49 | pmid=8863034 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8863034  }} </ref>


====Quantitative Stool Analysis====
====Quantitative Stool Analysis====
* A 48 or 72-hour quantitative stool collection may sometimes may be useful in the evaluation of acute diarrhea in patients.  
* A 48 or 72-hour quantitative [[Human feces|stool]] collection may sometimes may be useful in the evaluation of acute diarrhea in patients.  
* Full analysis of the collection includes measurement of:
* Full analysis includes measurement of:
** Stool weight
** Stool weight
** Stool fat content  
** Stool fat content  
** Stool osmolality  
** Stool osmolality  
** Stool electrolyte concentrations
** Stool electrolyte concentrations
** Magnesium concentration and output
** [[Magnesium|Magnesium levels]]
** Stool pH  
** Stool pH  
** Stool occult blood
** [[Occult blood|Stool occult blood]]
** Fecal chymotrypsin  
** [[Chymotrypsin|Fecal chymotrypsin]]
** Fecal elastase activity  
** [[Fecal elastase|Fecal elastase activity]]
** Prior to collection period, patient should eat a regular diet containing adequate amounts of calories and fat. All medications, especially antidiarrheal medications should be avoided.
** Prior to collection period, patient should eat a regular diet containing adequate amounts of calories and fat. All medications, especially antidiarrheal medications should be avoided.


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* Stool weight is also a useful index in the diagnosis of acute diarrhea.  
* Stool weight is also a useful index in the diagnosis of acute diarrhea.  
* Stool weight of >200g/day is considered diarrheal.  
* Stool weight of >200g/day is considered diarrheal.  
* Low stool weight with increased frequency of stools may be indicative of incontinence or pain.  
* Low stool weight with increased frequency of stools may be indicative of [[incontinence]] or pain.  
* Cessation of diarrhea with fasting is indicative of osmotic diarrhea caused by nonabsorbable substances or secretory diarrhea due to laxatives.<ref name="pmid6051321">{{cite journal| author=Fordtran JS| title=Speculations on the pathogenesis of diarrhea. | journal=Fed Proc | year= 1967 | volume= 26 | issue= 5 | pages= 1405-14 | pmid=6051321 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6051321  }} </ref>  
* Cessation of diarrhea with fasting is indicative of osmotic diarrhea caused by nonabsorbable substances or secretory diarrhea due to [[Laxative|laxatives]].<ref name="pmid6051321">{{cite journal| author=Fordtran JS| title=Speculations on the pathogenesis of diarrhea. | journal=Fed Proc | year= 1967 | volume= 26 | issue= 5 | pages= 1405-14 | pmid=6051321 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6051321  }} </ref>  


=====Stool Osmotic Gap=====
=====Stool Osmotic Gap=====
* The stool osmotic gap is calculated from electrolyte concentrations in stool water by the following formula : 290 - 2([Na+] + [K+]).
* The stool osmotic gap is calculated from [[Electrolyte|electrolyte concentrations]] in [[Human feces|stool]] water by the following formula : 290 - 2([Na+] + [K+]).
* The osmolality of stool within the distal intestine should be used for this calculation rather than the osmolality measured in fecal fluid, because measured fecal osmolality begins to increase in the collection container almost immediately when carbohydrates are converted by bacterial fermentation to osmotically active organic acids.  
* The [[Osmolarity|osmolality]] of stool present in the [[Intestine|distal intestine]] is preferred over [[Feces|fecal]] fluid, as measured osmolality of [[Feces|fecal]] fluid increases with [[Fermentation|bacterial fermentation]] of [[Carbohydrate|carbohydrates]] to osmotically active [[Organic acid|organic acids]].  
* Osmotic diarrheas, where electrolytes account for most of stool osmolality, are characterized by osmotic gaps >125 mOsm/kg, whereas secretory diarrheas where nonelectrolytes account for most of the osmolality of stool water, typically have osmotic gaps <50 mOsm/kg. In mixed cases, such in modest carbohydrate malabsorption (in which most of the carbohydrate load is converted to organic anions that obligate the fecal excretion of cations including Na+ and K+), the osmotic gap may lie between 50 and 125.<ref name="pmid1634072">{{cite journal| author=Eherer AJ, Fordtran JS| title=Fecal osmotic gap and pH in experimental diarrhea of various causes. | journal=Gastroenterology | year= 1992 | volume= 103 | issue= 2 | pages= 545-51 | pmid=1634072 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1634072  }} </ref>
* Stool osmotic gap in cases of osmotic diarrhea is characterized by osmotic gaps >125 mOsm/kg and in secretory diarrheas, osmotic gap is <50 mOsm/kg.  
* In mixed cases, the osmotic gap lies between 50-125mOsm/kg.<ref name="pmid1634072">{{cite journal| author=Eherer AJ, Fordtran JS| title=Fecal osmotic gap and pH in experimental diarrhea of various causes. | journal=Gastroenterology | year= 1992 | volume= 103 | issue= 2 | pages= 545-51 | pmid=1634072 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1634072  }} </ref>


=====Fecal pH=====
=====Fecal pH=====
* A fecal pH of < 5.3 indicates that carbohydrate malabsorption (such as that associated with lactulose or sorbitol ingestion) is a major cause of diarrhea.
* A [[Fecal pH test|fecal pH]] of < 5.3 is indicative of [[Malabsorption|carbohydrate malabsorption]].
* A pH of > 5.6 argues against carbohydrate malabsorption as the only cause and malabsorption syndrome that involves fecal loss of amino acids and fatty acids in addition to carbohydrate, have a higher fecal pH.<ref name="pmid1634072">{{cite journal| author=Eherer AJ, Fordtran JS| title=Fecal osmotic gap and pH in experimental diarrhea of various causes. | journal=Gastroenterology | year= 1992 | volume= 103 | issue= 2 | pages= 545-51 | pmid=1634072 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1634072  }} </ref>
* A [[Fecal pH test|fecal pH]] of > 5.6 may exclude [[Malabsorption|carbohydrate malabsorption]] as the cause of acute diarrhea.<ref name="pmid1634072">{{cite journal| author=Eherer AJ, Fordtran JS| title=Fecal osmotic gap and pH in experimental diarrhea of various causes. | journal=Gastroenterology | year= 1992 | volume= 103 | issue= 2 | pages= 545-51 | pmid=1634072 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1634072  }} </ref>


=====Fecal Fat Concentration and Output=====
=====Fecal Fat Concentration and Output=====
* The upper limit of fecal fat output measured in normal subjects (without diarrhea) ingesting normal amounts of dietary fat is approximately 7 g/day (9% of dietary fat intake)and values more than this signify the presence of steatorrhea.
* In normal subjects, [[fecal fat]] ouput is approximately 9% of dietary fat intake (7g/day).
* A fecal fat concentration of <9.5 g/100 g of stool more likely to be seen in small intestinal malabsorptive syndromes because of the diluting effects of coexisting fluid malabsorption.<ref name="pmid6735076">{{cite journal| author=Bo-Linn GW, Fordtran JS| title=Fecal fat concentration in patients with steatorrhea. | journal=Gastroenterology | year= 1984 | volume= 87 | issue= 2 | pages= 319-22 | pmid=6735076 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6735076  }} </ref>
* [[Fecal fat]] levels >7g/day are suggestive of steatorrhea.
* A fecal fat concentrations of ≥9.5 g/100 g of stool were seen in pancreatic and biliary [[steatorrhea]], in which fluid absorption in the small bowel is intact.<ref name="pmid20814209">{{cite journal| author=Hammer HF| title=Pancreatic exocrine insufficiency: diagnostic evaluation and replacement therapy with pancreatic enzymes. | journal=Dig Dis | year= 2010 | volume= 28 | issue= 2 | pages= 339-43 | pmid=20814209 | doi=10.1159/000319411 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20814209 }} </ref>
* [[Fecal fat]] concentration of <9.5 g/100 g of stool: Small intestinal malabsorptive syndromes<ref name="pmid6735076">{{cite journal| author=Bo-Linn GW, Fordtran JS| title=Fecal fat concentration in patients with steatorrhea. | journal=Gastroenterology | year= 1984 | volume= 87 | issue= 2 | pages= 319-22 | pmid=6735076 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6735076  }} </ref>
 
* [[Fecal fat]] concentrations of ≥9.5 g/100 g of stool: [[Pancreas|Pancreatic]] and [[Bile duct|biliary]] [[steatorrhea]]<ref name="pmid20814209">{{cite journal| author=Hammer HF| title=Pancreatic exocrine insufficiency: diagnostic evaluation and replacement therapy with pancreatic enzymes. | journal=Dig Dis | year= 2010 | volume= 28 | issue= 2 | pages= 339-43 | pmid=20814209 | doi=10.1159/000319411 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20814209  }} </ref>
=====Analysis for Laxatives=====
Analysis for laxatives should be done early in the evaluation of diarrhea of unknown etiology.  The simplest test for a laxative is alkalinization of 3 mL of stool supernatant or urine with one drop of concentrated sodium hydroxide and a pink or red color is a positive result.  Stool water can be analyzed specifically for phenolphthalein, emetine and bisacodyl and its metabolites, using chromatographic or chemical tests.  Urine can be analyzed for anthraquinone derivatives.
 
* If stool electrolyte analysis suggests secretory diarrhea (osmotic gap <50), the patient may have ingested a laxative capable of causing secretory diarrhea, such as sodium sulfate or sodium phosphate ingestion.<ref name="pmid8193462">{{cite journal| author=Carlson J, Fernlund P, Ivarsson SA, Jakobsson I, Neiderud J, Nilsson KO et al.| title=Munchausen syndrome by proxy: an unexpected cause of severe chronic diarrhoea in a child. | journal=Acta Paediatr | year= 1994 | volume= 83 | issue= 1 | pages= 119-21 | pmid=8193462 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8193462  }} </ref>
* If stool electrolyte analysis suggests osmotic diarrhea (osmotic gap >125 mOsm/kg), magnesium (Mg2+) laxatives may have been ingested.<ref name="pmid2005938">{{cite journal| author=Fine KD, Santa Ana CA, Fordtran JS| title=Diagnosis of magnesium-induced diarrhea. | journal=N Engl J Med | year= 1991 | volume= 324 | issue= 15 | pages= 1012-7 | pmid=2005938 | doi=10.1056/NEJM199104113241502 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2005938  }} </ref>
* If fecal osmolality is significantly less than 290 mOsm/kg (the osmolality of plasma), water or hypotonic urine has been added to the stool.
* If the osmolality is far above that of plasma, hypertonic urine may have been added to stool.  Urinary contamination can be confirmed by a finding of high monovalent cation concentration (e.g., [Na+] + [K+] > 165, physiologically impossible in stool water) and a high concentration of urea or creatinine in stool water.
 
====Tests for Bacterial Overgrowth====
* The gold standard for diagnosis of [[bacterial overgrowth]] has been quantitative culture of an aspirate of luminal fluid and specifically a positive jejunal culture (>106 organisms/mL) in chronic diarrhea patients can be considered evidence of clinically significant bacterial overgrowth in the upper small intestine.<ref name="pmid24095975">{{cite journal| author=Saad RJ, Chey WD| title=Breath Testing for Small Intestinal Bacterial Overgrowth: Maximizing Test Accuracy. | journal=Clin Gastroenterol Hepatol | year= 2013 | volume=  | issue=  | pages=  | pmid=24095975 | doi=10.1016/j.cgh.2013.09.055 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=24095975 }} </ref>


* A breath test using [14C] glycocholate is used to test bacterial overgrowth. The radiolabeled conjugated [[bile acid]] is deconjugated by the bacteria, and the 14C in the side chain is metabolized to 14CO2, which is exhaled.
=====Analysis for Laxative Abuse=====
 
Stool analysis for [[Laxative|laxatives]] is done in the assesment of diarrhea of unknown cause. This includes the following techniques:
*Another 14C-breath test using [14C] [[xylose]], nonradioactive glucose and nonradioactive [[lactulose]] have been developed to test bacterial overgrowth.<ref name="pmid2295385">{{cite journal| author=Corazza GR, Menozzi MG, Strocchi A, Rasciti L, Vaira D, Lecchini R et al.| title=The diagnosis of small bowel bacterial overgrowth. Reliability of jejunal culture and inadequacy of breath hydrogen testing. | journal=Gastroenterology | year= 1990 | volume= 98 | issue= 2 | pages= 302-9 | pmid=2295385 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2295385 }} </ref>
* Treatment of 3ml of [[Human feces|stool]] supernatant or [[urine]] with a single drop of concentrated [[Sodium hydroxide|NaOH]] with resulting pink or red color, due to [[Alkali|alkalinization]] is the simplest test for [[Laxative|laxatives]].
 
* [[Stool examination|Analysis of stool]] using [[chromatography]] for [[emetine]], [[bisacodyl]] and its metabolites, [[phenolphthalein]], etc may also be performed.
* An elevated concentration of hydrogen in breath after overnight fasting also has been proposed as an insensitive but specific marker of small intestinal bacterial overgrowth.  This elevated hydrogen concentration may also be seen in patients with malabsorption syndrome.
* Calculation of stool osmotic gap may be helpful in pinpointing the [[laxative]] responsible for acute diarrhea:
 
** Stool osmotic gap <50: [[Sodium sulfate]] or [[Sodium phosphates|sodium phosphate]]<ref name="pmid8193462">{{cite journal| author=Carlson J, Fernlund P, Ivarsson SA, Jakobsson I, Neiderud J, Nilsson KO et al.| title=Munchausen syndrome by proxy: an unexpected cause of severe chronic diarrhoea in a child. | journal=Acta Paediatr | year= 1994 | volume= 83 | issue= 1 | pages= 119-21 | pmid=8193462 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8193462 }} </ref>
* An abnormal [[Schilling test|Schilling II test]] result (radiolabeled B12 given with intrinsic factor) that normalizes after therapy with broad-spectrum antibiotics has also been considered as a test for small intestinal bacterial overgrowth (the so-called Schilling III test).<ref name="pmid5762651">{{cite journal| author=| title=Schilling test of vitamin B12 absorption. | journal=Br Med J | year= 1969 | volume= 1 | issue= 5639 | pages= 300-1 | pmid=5762651 | doi= | pmc=PMC1982167 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=5762651 }} </ref>
** Stool osmotic gap >125 mOsm/kg: [[Magnesium]] [[Laxative|laxatives]]<ref name="pmid2005938">{{cite journal| author=Fine KD, Santa Ana CA, Fordtran JS| title=Diagnosis of magnesium-induced diarrhea. | journal=N Engl J Med | year= 1991 | volume= 324 | issue= 15 | pages= 1012-7 | pmid=2005938 | doi=10.1056/NEJM199104113241502 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2005938 }} </ref>


==References==
==References==
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sudarshana Datta, MD [2]

Overview

Laboratory investigations performed in the evaluation of patients with acute diarrhea include spot stool analysis, detection of occult blood, white blood cells, stool culture, quantitative stool analysis, fecal weight, stool osmotic gap, fecal pH, fecal fat concentration and analysis for laxative abuse. According to the ACG guidelines, stool culture is done only in cases where the patient is at high risk of spreading the disease to others. Stool diagnostic studies are performed when symptoms last for >7 days, patient has dysentery or moderate-to-severe diarrhea and to determine etiology to enable directed pathogen-specific therapy. Antibiotic sensitivity testing for management of acute diarrhea is not advised.

Laboratory Findings

Laboratory investigations performed in the workup of patients with acute diarrhea include complete blood count, glucose levels, white blood cells (WBC) detection, urine analysis, calcium levels, Thyroid stimulating hormone (TSH) levels, complete metabolic panel and stool examination.

Laboratory Evaluation of Acute Diarrhea

Spot Stool Analysis

  • Stool spot analysis is preferred over 24 hour stool collection as it is less cumbersome.
Occult Blood
White Blood Cells
Stool Culture

Quantitative Stool Analysis

  • A 48 or 72-hour quantitative stool collection may sometimes may be useful in the evaluation of acute diarrhea in patients.
  • Full analysis includes measurement of:
Fecal Weight
  • Stool weight is also a useful index in the diagnosis of acute diarrhea.
  • Stool weight of >200g/day is considered diarrheal.
  • Low stool weight with increased frequency of stools may be indicative of incontinence or pain.
  • Cessation of diarrhea with fasting is indicative of osmotic diarrhea caused by nonabsorbable substances or secretory diarrhea due to laxatives.[6]
Stool Osmotic Gap
Fecal pH
Fecal Fat Concentration and Output
Analysis for Laxative Abuse

Stool analysis for laxatives is done in the assesment of diarrhea of unknown cause. This includes the following techniques:

References

  1. ↑ Viana Freitas BR, Kibune Nagasako C, Pavan CR, Silva Lorena SL, Guerrazzi F, Saddy Rodrigues Coy C; et al. (2013). "Immunochemical fecal occult blood test for detection of advanced colonic adenomas and colorectal cancer: comparison with colonoscopy results". Gastroenterol Res Pract. 2013: 384561. doi:10.1155/2013/384561. PMC 3844264. PMID 24319453.
  2. ↑ Fine KD (1996). "The prevalence of occult gastrointestinal bleeding in celiac sprue". N Engl J Med. 334 (18): 1163–7. doi:10.1056/NEJM199605023341804. PMID 8602182.
  3. ↑ Kane SV, Sandborn WJ, Rufo PA, Zholudev A, Boone J, Lyerly D; et al. (2003). "Fecal lactoferrin is a sensitive and specific marker in identifying intestinal inflammation". Am J Gastroenterol. 98 (6): 1309–14. doi:10.1111/j.1572-0241.2003.07458.x. PMID 12818275.
  4. ↑ Friedman M, Ramsay DB, Borum ML (2007). "An unusual case report of small bowel Candida overgrowth as a cause of diarrhea and review of the literature". Dig Dis Sci. 52 (3): 679–80. doi:10.1007/s10620-006-9604-4. PMID 17277989.
  5. ↑ Koontz F, Weinstock JV (1996). "The approach to stool examination for parasites". Gastroenterol Clin North Am. 25 (3): 435–49. PMID 8863034.
  6. ↑ Fordtran JS (1967). "Speculations on the pathogenesis of diarrhea". Fed Proc. 26 (5): 1405–14. PMID 6051321.
  7. ↑ 7.0 7.1 Eherer AJ, Fordtran JS (1992). "Fecal osmotic gap and pH in experimental diarrhea of various causes". Gastroenterology. 103 (2): 545–51. PMID 1634072.
  8. ↑ Bo-Linn GW, Fordtran JS (1984). "Fecal fat concentration in patients with steatorrhea". Gastroenterology. 87 (2): 319–22. PMID 6735076.
  9. ↑ Hammer HF (2010). "Pancreatic exocrine insufficiency: diagnostic evaluation and replacement therapy with pancreatic enzymes". Dig Dis. 28 (2): 339–43. doi:10.1159/000319411. PMID 20814209.
  10. ↑ Carlson J, Fernlund P, Ivarsson SA, Jakobsson I, Neiderud J, Nilsson KO; et al. (1994). "Munchausen syndrome by proxy: an unexpected cause of severe chronic diarrhoea in a child". Acta Paediatr. 83 (1): 119–21. PMID 8193462.
  11. ↑ Fine KD, Santa Ana CA, Fordtran JS (1991). "Diagnosis of magnesium-induced diarrhea". N Engl J Med. 324 (15): 1012–7. doi:10.1056/NEJM199104113241502. PMID 2005938.

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