Stool examination

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Vishal Devarkonda, M.B.B.S[2]

Indications

Common indication for stool analysis in general practice are

Specimen collection

• Collect the stool in a dry, clean, leakproof container. Make sure no urine, water, soil or other material gets in the container.
• The image on the right demonstrates the distribution of protozoa in relation to stool consistency and should be taken into consideration when specimens are received.
• Fresh stool should be examined, processed, or preserved immediately.  An exception is specimens kept under refrigeration when preservatives are not available; these specimens are suitable for antigen testing only.
• Preserve the specimen as soon as possible.  If using a commercial collection kit, follow the kit's instructions.  If kits are not available, the specimen should be divided and stored in two different preservatives, 10% formalin and PVA (polyvinyl-alcohol), using suitable containers.  Add one volume of the stool specimen to three volumes of the preservative.
• Insure that the specimen is mixed well with the preservative.  Formed stool needs to be well broken up.
• Insure that the specimen containers are sealed well.  Reinforce with parafilm or other suitable material.  Insert the container in a plastic bag.
• Certain drugs and compounds will render the stool specimens unsatisfactory for examination.  The specimens should be collected before these substances are administered, or collection must be delayed until after the effects have passed.  Such substances include: antacids, kaolin, mineral oil and other oily materials, non-absorbable antidiarrheal preparations, barium or bismuth (7-10 days needed for clearance of effects), antimicrobial agents (2-3 weeks), and gallbladder dyes (3 weeks).
• Specimen collection may need to be repeated if the first examination is negative.  If possible, three specimens passed at intervals of 2-3 days should be examined.

Preservation of specimens

• Preservation of specimens is necessary when stool specimens cannot be examined within the prescribed time interval.  Various preservatives are available, with the two most commonly used being 10% aqueous formalin and PVA (polyvinyl-alcohol). 

PCR

• If PCR is being requested on a stool specimen, the specimen must be collected in a preservative that is compatible with molecular detection. Fixatives/preservatives with acceptable performance for PCR include TotalFix, Unifix, modified PVA (Zn- or Cu-based), and Ecofix. Stool specimens in these preservatives can be stored and shipped at room temperature. Alternatively, stool specimens can be collected in a clean vial and kept unpreserved; however, these specimens must be stored cold or frozen and shipped either refrigerated (4°C) or frozen (shipped with dry ice). Trichrome stained smears (for E. histolytica/E. dispar) or acid-fast smears (for C. parvum or C. cayetanensis) should accompany the stool specimen when requesting PCR for any of these protozoa.  All stained smears will be read first and if an identification of the parasite can be made, PCR will not be performed. 

Analysis

Appearance

Shape

Consistency

Color

Chemical test

PH

Electrolytes

Osmolarity

Antigen essay

Fat

Blood

Bile