Acute diarrhea laboratory findings

Acute Diarrhea Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Acute Diarrhea from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
Diagnostic Study of Choice
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
Echocardiography and Ultrasound
CT scan
MRI
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
Cost-Effectiveness of Therapy
Future or Investigational Therapies
Guidelines for Management
Case Studies
Case #1
Acute diarrhea laboratory findings On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
American Roentgen Ray Society Images of Acute diarrhea laboratory findings All Images X-rays Echo & Ultrasound CT Images MRI
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Acute diarrhea laboratory findings
CDC on Acute diarrhea laboratory findings
Acute diarrhea laboratory findings in the news
Blogs on Acute diarrhea laboratory findings
Directions to Hospitals Treating Psoriasis
Risk calculators and risk factors for Acute diarrhea laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Overview

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

OR

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 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 (LFTs), Blood urea nitrogen (BUN) / creatinine levels, Hepatitis serologies and stool examination.

• Stool examination includes the following:
  • Stool culture
  • Stool electrolytes
  • Stool osmolality
  • Ova and parasites
  • Fecal lactoferrin
  • Fecal leukocytes
  • Test for C. difficile

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

• A positive test result suggests the presence of inflammatory bowel disease and acute causes of bloody diarrhea.
• Fecal occult blood positivity may also be associated with diarrhea due to idiopathic secretory diarrhea, laxative abuse, and microscopic colitis.

White Blood Cells

• Wright's staining and microscopy is the standard method for the detection of white blood cells (WBCs) present in stool.
• Neutrophils in the stool present in patients having acute infectious diarrhea may be detected by latex agglutination test.

Stool Culture

• In 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 Pleisiomonas species.
• In immunocompromised patients, stool culture is included as a part of routine investigations to rule out infection dur to Samonella, Campylobacter, protozoa and fungi.

• Protozoa may detected by the use of fecal enzyme-linked immunosorbent assay (ELISA).

Quantitative Stool Analysis

A 48- or 72-hour quantitative stool collection is useful in the work-up of chronic diarrhea. Full analysis of the collection includes measurement of weight, fat content, osmolality, electrolyte concentrations, magnesium concentration and output, pH, occult blood, and based upon the history fecal chymotrypsin or elastase activity and laxatives. Several days before and during the collection period, the patient should eat a regular diet of moderately high fat content or a fixed diet for some patients to ensure that adequate amounts of fat and calories are consumed. During the collection period, no diagnostic tests should be done that would disturb the normal eating pattern, aggravate diarrhea, diminish diarrhea, add foreign material to the gut, or risk an episode of incontinence. All but essential medications should be avoided, and any antidiarrheal medication begun before the collection period should be held.

Fecal Weight

• Knowledge of stool weight is of direct help in diagnosis and management in some instances. Stool weights greater than 500 g/day are rarely if ever seen in patients with irritable bowel syndrome and stool weights less than 1000 g/day are evidence against pancreatic syndrome.

• Low stool weight in a patient complaining of “severe diarrhea” suggests that incontinence or pain may be the dominant problem.

• Response to fasting such as complete cessation of diarrhea during fasting is strong evidence that the mechanism of diarrhea involves something ingested (nonabsorbable substance or nutrient causing osmotic diarrhea, or unabsorbed fatty acids or laxatives causing secretory diarrhea).

Stool Osmotic Gap

• The osmotic gap is calculated from electrolyte concentrations in 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.
• 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.

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 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.

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.
• 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.
• 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.

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.
• If stool electrolyte analysis suggests osmotic diarrhea (osmotic gap >125 mOsm/kg), magnesium (Mg2+) laxatives may have been ingested.
• 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.

• 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.

• Another 14C-breath test using [14C] xylose, nonradioactive glucose and nonradioactive lactulose have been developed to test bacterial overgrowth.

• 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.

• An abnormal 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).