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Clinical Pathology

Stool Test: Significance, Procedure, Results & Types

By Dayyal Dg.Twitter Profile | Updated: Tuesday, 04 June 2024 08:38 UTC
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A doctor's hand in a white medical glove holds a stool sample on a stick and a container for stool analysis on a yellow background. The medicine. Analysis. Cala. Infection. The close plan.
A doctor's hand in a white medical glove holds a stool sample on a stick and a container for stool analysis on a yellow background. The medicine. Analysis. Cala. Infection. The close plan. Unsplash / @diana_pole

Materials expelled from the human digestive system predominantly consist of water, constituting up to 75% of the total composition. This is accompanied by food particles that have undergone the process of digestion but have not been assimilated, indigestible remnants, and undigested food substances. The presence of epithelial cells, bile, a variety of bacteria, and secretions from the digestive tract further contribute to the complexity of this waste matter. Additionally, inorganic bacterial components are also a part of this intricate mix. Under normal physiological conditions, an adult human being typically excretes between 100 and 200 grams of fecal matter on a daily basis.

The examination of stool, often referred to as a stool test or stool analysis, is a critical diagnostic procedure employed by medical professionals to evaluate the health status and functionality of an individual’s gastrointestinal tract. This comprehensive analysis involves the meticulous collection and subsequent examination of a fecal sample, offering a wealth of insights into numerous facets of digestive health and overall physiological well-being.

The procedure encompasses a thorough investigation of the stool’s characteristics, including its color, consistency, volume, form, and odor, along with the potential presence of mucus. Moreover, the stool is scrutinized for concealed elements such as occult blood, fats, meat fibers, bile, white blood cells, and specific sugars known as reducing substances. The pH level of the stool, an important indicator of digestive health, is also accurately measured during this examination.

Examination of stool is very helpful in the diagnosis of disease of the gastrointestinal tract as listed below.

Detection of parasites

The procedure of stool examination is meticulously conducted with the primary objective of detecting and identifying parasitic organisms. This includes various forms of helminths, encompassing adult worms, their larval stages, worm segments, and eggs. Additionally, the presence of protozoan parasites, in both their cystic and trophozoite stages, is also diligently sought during this comprehensive analysis.

Bacteriologic examination

The procedure of stool culture is executed with the primary objective of assessing potential bacterial infections. This includes infections caused by various bacterial species such as Clostridium difficile, Yersinia, Salmonella, Shigella, or Vibrio. Furthermore, this comprehensive analysis also facilitates the identification of bacterial toxins, including those produced by Clostridium difficile or Clostridium botulinum.

Evaluation of chronic diarrhea

Chronic diarrhea is characterized by the occurrence of three or more instances of loose or liquid stools per day, persisting for a duration exceeding four weeks. Conversely, acute diarrhea is identified by the same frequency of loose or liquid stools, but with a duration less than four weeks. The examination of stool samples plays a pivotal role in the laboratory investigations associated with diarrhea.

The nature of the investigation dictates whether a random stool sample or a 72-hour or 48-hour sample is collected. Tests for occult blood, pH, fat, white blood cells, microscopy, or culture typically utilize a random stool sample. In contrast, a 72-hour or 48-hour sample is collected and analyzed for parameters such as weight, carbohydrate and fat content, osmolality, or chymotrypsin activity.

The causes of both chronic and acute diarrhea are enumerated in Table 1 and Flowchart 1, respectively.

Table 1: Classification and causes of chronic diarrhea
Watery diarrheaInflammatory diarrheaFatty diarrhea
  1. Osmotic
    • Carbohydrate malabsorption
    • Osmotic laxatives
  2. Secretory
    • Bacterial toxins
    • Bile acid malabsorption
    • Laxative abuse
    • Hormonal disorders: VIPoma, carcinoid syndrome, gastrinoma, hyperthyroidism
  1. Invasive bacterial and parasitic infections
  2. Inflammatory bowel disease
  3. Pseudomembranous colitis
  4. Infectious diseases
  5. Neoplasia
Malabsorption syndromes
  • Acute diarrhea
    • Infectious
      • Watery
        • Enterotoxigenic Escherichia coli (ETEC)
          Enteropathogenic Escherichia coli (EPEC)
          Staphylococcus aureus
          Vibrio cholerae
          Clostridium perfringens
          Adenovirus (Enteric)
      • Dysentery
        • Shigella spp.
          Enteroinvasive Escherichia coli (EIEC)
          Enterohemorrhagic Escherichia coli (EHEC)
          Campylobacter spp.
          Clostridium difficile
          Entamoeba histolytica
    • Non-infectious
      • Food intolerance
        Inflammatory bowel disease
        Carcinoid syndrome
        Thyroid disease

Evaluation of dysentery

The distinction between bacillary dysentery and amebic dysentery is achieved through the identification of the respective causative organism present in the stool.

Detection of Rotavirus

Rotavirus is the predominant cause of diarrhea in infants and young children. The presence of Rotavirus can be confirmed through the electron microscopic examination of stool samples. Additional methods, such as latex agglutination, immunofluorescence, or enzyme-linked immunosorbent assay (ELISA), are also employed for the detection of Rotavirus in stool samples.

Chemical examination

Chemical analyses can be conducted on fecal samples to identify various conditions. These include the detection of excessive fat excretion, indicative of malabsorption syndrome, the presence of occult blood, which may suggest ulcerated lesions in the gastrointestinal tract or potential occult carcinoma of the colon, and the determination of the presence or absence of urobilinogen, a marker for obstructive jaundice.

Differentiating infection by invasive bacteria (like Salmonella or Shigella) from that due to toxin-producing bacteria (like Vibrio cholerae or Escherichia coli)

The examination of fecal samples includes the detection of white blood cells. An elevated count of polymorphonuclear neutrophils, identifiable by the presence of granules in their cytoplasm via methylene blue staining, is observed as depicted in Flowchart 2.

  • Acute diarrhea
    • Examination of feces for white blood cells
      • White blood cells present
        • Shigella spp
          Campylobacter spp
          Enteroinvasive Escherichia coli (EIEC)
      • White blood cells absent
        • Enterotoxigenic Escherichia coli (ETEC)
          Enteropathogenic Escherichia coli (EPEC)
          Vibrio cholerae
          Staphylococcus aureus
          Adenovirus (Enteric)
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