How to Collect a Stool Sample for Stool Tests

Abstract

A stool sample contains parasites or eggs (ova) that are linked to intestinal infections. It is very important to follow the instructions and use given by the laboratory staff for collecting stool sample. The Stool Sample is normally requested for stool analysis. Stool analysis is done to:

It is used to screen for colon cancer through fecal occult blood test
It is also used to diagnose peptic ulcers disease by H.pylori Ag test
Its is also used to diagnose parasites, such as pinworms or Giardia
Used to check for unknown cause of an infection, like bacteria, a fungus, or a virus.
Used to find out poor absorption of nutrients by the digestive tract (malabsorption syndrome). For this test, all stool is collected over a 72-hour period and then checked for fat (and sometimes for meat fibres). This test is called a 72-hour stool collection or quantitative fecal fat test.
Used to find out diseases of the digestive tract, liver, and pancreas.
Use to look for enzymes (such as trypsin or elastase) may be evaluated in the stool to help see functionality of the pancreas.
Used to know the symptoms affecting the digestive tract, such as prolonged diarrhea, bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of appetite, bloating, belly pain and cramping, and fever.

A stool sample usually has parasites or eggs (ova) that are connected to intestinal infections. It is very important to follow the instructions given by the laboratory staff for collecting the stool sample.

NB:

To successfully diagnose and identify parasites, a laboratory requires the knowledge and practice of laboratory testing in the pre-analytic, analytic, and post-analytic steps. For example, in the pre-analytic phase, a specimen received in the laboratory that is compromised because of improper collection, labeling, or transport should be rejected and a new specimen requested.
Similarly, laboratory techniques performed in the analytic phase of testing of these samples should be completed with care to ensure that accurate results arebtained.
Interpretation and reporting of results obtained, completed in the post analytic phase of testing, should be accurately reported in a timely manner.

Stool sample for Ova and parasite examination

The commonly performed procedure in the area of parasitology is the examination of a stool specimen for ova and parasites (abbreviated as O&P), where ova are to the egg stage of select parasites and parasites encompasses the other morphologic forms that may be present. There are two general components associated with this routine parasitology procedure macroscopic and microscopic examination.

A a small plastic container called a stool container is used to collect the stool sample.
Clients name, date of birth and the date on the is written on the container.

To collect a poo sample:

Place something in the toilet to catch the stool, like a clean disposable container, or spread newspaper or cling film (plastic wrap) over the rim of the toilet.
Pass poo making sure it does not touch the inside of the toilet, or the water.
Use a deposable spoon to pick some stool in the container. Usually, the container comes with a spoon.
Pick any stool that’s watery or has blood or slime in it.
Fill the container just under halfway with stool, then screw the lid shut.
Flush the rest of the stool down the toilet.
Put everything you’ve used to collect the stool in a plastic bag, tie it up and put it in the bin.
Wash hands with soap and warm running water.

Important considerations in collecting fecal specimens

Because parasites are often shed (i.e. enter and subsequently passed in the stool) intermittently, they may not appear in a stool specimen on a daily basis; therefore, multiple specimens are recommended for optimum detection. The typical stool collection protocol consists of three specimens, one specimen collected every other day or a total of three collected in 10 days. One exception is in the diagnosis of amebiasis, in which up to six specimens in 14 days is acceptable.
Certain medications and substances can interfere with the detection of parasites. Stool samples from patients whose therapy includes barium, bismuth, or mineral oil must be collected prior to therapy or not until 5 to 7 days after the completion of therapy. If the samples are taken during the course of therapy, these interfering substances may mask possible parasites during examination. Collection of specimens from patients who have taken antibiotics or antimalarial medications should be delayed for 2 weeks following therapy.
Stool sample must be collected in a clean, watertight container with a tight-fitting lid. The acceptable amount of stool required for parasite study is 2 to 5 g, often referred to as the size of a walnut. Urine must not be allowed to contaminate the stool specimen because it has been known to destroy some parasites.
Stool should not be retrieved from toilet bowl water because free-living protozoa and nematodes may be confused with human parasites. In addition, water may destroy select parasites, such as schistosome eggs and amebic trophozoites.
Toilet tissue in the stool specimen may mask parasites or make examination of the sample difficult.
The stool container should be labeled with the patient’s name and identification number, the physician’s name, and the date and time of sample collection. Some form of requisition, paper or computer-based, should accompany the specimen indicating the test(s) requested. Other information, such as suspected diagnosis, travel history, and clinical findings, is helpful, but may not be provided.
The stool sample should be placed into a zip lock plastic bag for transport to the laboratory. The paperwork accompanying the specimen should be separated from the specimen container.
When collecting handling all specimens, gloves and a protective coat must be worn at all times. Biohazard hoods should also be used in laboratories, when present. Universal precautions, as outlined by the Occupational Safety and Health Administration (OSHA) for handling blood and body fluids, should be exhibited and enforced at all times.
Another important consideration in testing fecal specimens for parasites is the time frame from sample collection to receipt and examination in the laboratory. To demonstrate the motility of protozoan trophozoites, a fresh stool sample is needed. The trophozoite stage is sensitive to environmental changes and, on release from the body, disintegrates rapidly. Other parasite stages (e.g., protozoan cysts, helminth eggs and larvae) are not as sensitive and can survive for longer periods outside the host. Because trophozoites are usually found in liquid stool, it is recommended that liquid specimens be examined within 30 minutes of passage. In keeping with stool consistency, semi-formed specimens may yield a mixture of protozoan cysts and trophozoites and should be evaluated within 1 hour of passage. Formed stool specimens are not likely to contain trophozoites; therefore, they can be held for 24 hours following collection. If these guidelines cannot be met, the specimen should be placed into a preservative. The specimen can be preserved by placing it directly into a fixative at the time it is collected or on receipt in the laboratory

Transportation of stool sample

Morphologic forms of protozoa and helminths can be detected from a properly collected and prepared stool sample. When present, the protozoan forms known as trophozoites and cysts may be recovered from these samples. Helminth stages, such as eggs, larvae, proglottids, and adult worms, may also be found

Fixatives for Preservation

A freshly collected stool sample, which is immediately submitted to the laboratory, is the ideal specimen for parasitic examination. When this is not possible, the sample must be preserved to maintain its integrity. Therefore fixatives are substances that preserve the morphology of protozoa and prevent further development of certain helminth eggs and larvae. Several preservatives are available commercially.

The ratio of fixative to stool is important for the successful recovery of parasites and, whatever fixative is used, the recommended ratio is three parts fixative to one part stool. Commercial kits may contain one or more vials, each containing an appropriate preservative. These kits usually contain vials with fill lines marked to indicate the appropriate sample volume.

It is also important that the specimen be mixed well with the preservative to achieve thorough fixation. Because the patient is often responsible for collection of the specimen and transfer to the fixative vials, it is imperative that he or she be given detailed and complete instructions.

The specimen must be fixed in the preservative for at least 30 minutes before processing begins. The choice of fixative(s) for O&P is dependent on the preference of the laboratory performing the test. Because the laboratory ideally should have the ability to perform all steps of the O&P test, appropriate fixatives should be on hand to accomplish these steps.
Some fixatives are limited to use in certain O&P laboratory procedures. Thus, the laboratory technician must be familiar with and understand the uses and limitations of each fixative.

1. Polyvinyl Alcohol.

Polyvinyl alcohol (PVA) is made up of a plastic powder that acts as an adhesive for the stool specimen when preparing slides for staining. PVA is most often combined with Schaudinn solution, which usually contains zinc sulfate, copper sulfate, or mercuric chloride as a base. Like formalin, PVA has advantages and disadvantages regarding its use.

Trophozoites and cysts of the protozoa, and also most helminth eggs, can be detected using this fixative. The greatest advantage of this preservative is that it can be used for preparation of a permanent stained smear. PVA-preserved specimens have a long shelf life when stored at room temperature. Although concentration techniques can also be performed from a PVA-preserved specimen, the recovery of certain parasites is not as effective as when formalin is used. Thus, many laboratories choose to use a two-vial system a formalin vial for the concentration technique and a PVA vial for the stained slide.

The biggest disadvantage of this preservative is that it contains mercuric chloride which has potential health problems. strict regulations regarding the use and disposal of PVA have resulted in many laboratories looking for alternatives.

2. Sodium Acetate Formalin.

An alternative to the use of PVA and Schaudinn fixative is sodium acetate formalin (SAF). This preservative can be used for performing concentration techniques and permanent stained smears. Some. Laboratories have adopted this fixative because it only requires a single vial and it is mercury-free.

SAF is easy to prepare, has a long shelf life, and can be used for preparing smears for staining with the modified acid-fast stain to detect coccidian oocysts. SAF also has disadvantages. Because the adhesive properties of SAF are not good, the addition of albumin to the microscope slide may be necessary to ensure adhesion of the specimen to the slide. Furthermore, protozoa morphology from SAF-preserved specimens is not as clear in permanent stains as when mercury-containing preservatives are used.

Another limiting factor of SAF is in the choice of permanent stains made from this fixative. Many experts believe that permanent stained smears with iron hematoxylin staining provide better results than staining SAF preserved material using the Wheatley trichrome stain

3. Modified Polyvinyl Alcohol.

Other alternatives to mercury-based PVA are the use of substitute compounds containing copper sulfate or zinc sulfate. The advantage of these formulas is that they can be used for concentration methods and permanent stained smears. However, these substitute products do not provide the same quality of preservation for adequate protozoan morphology on a permanent stained slide as the mercury-based fixatives.

Therefore, parasite identification will be more difficult. Zinc sulfate fixatives provide better results than copper sulfate reagents. Modified PVA fixatives are more likely to be negatively affected if proper protocol is not followed (e.g., stool-to-fixative ratio, adequate mixing).

4. Alternative Single-Vial Systems.

Many manufacturers have developed alternative nontoxic fixatives. These single-vial fixatives are free of formalin and mercury and can be used for concentration techniques and permanent stained smears. Some of these products may also be used for performing fecal immunoassays. Like the modified PVA fixatives, these products do not provide the same quality of preservation as mercury-based fixatives and organism identification will be more difficult from permanent stained slides

Processing

Once a stool specimen has arrived in the laboratory, the analytic phase of laboratory testing, also referred to processing, begins. In this phase, samples are examined from two perspectives, macroscopic and microscopic.