A stool sample is a non-invasive diagnostic tool used by medical professionals to assess the health and function of the gastrointestinal tract. Analyzing the specimen can help detect various conditions, including infectious diseases caused by bacteria, viruses, or parasites, inflammatory bowel diseases, and colorectal cancer. These tests provide specific information about the presence of hidden blood, genetic markers, or imbalances in the gut microbiome, offering valuable insight into the underlying causes of symptoms like chronic diarrhea, abdominal pain, or unexplained weight loss.
Required Amount Varies By Test Type
There is no single, universal quantity of stool required for testing, as the necessary amount depends entirely on the specific laboratory analysis ordered by a healthcare provider. The required volume is dictated by the method used to process the sample, such as molecular testing for infection versus a chemical test for blood. Always consult the instructions provided with the collection kit, as they contain the exact quantity needed for the test ordered.
For many common tests, such as a Fecal Immunochemical Test (FIT) used to screen for hidden blood, the required amount is small, often involving simply scraping the surface of the stool with a collection stick and inserting it into a vial. Other tests, like an Ova and Parasite (O&P) exam, which uses a microscope to identify organisms, often require a larger sample size to ensure a representative specimen is analyzed. For these tests, the instructions may ask for a piece of stool roughly the size of a walnut or a grape, which is typically 10 to 15 grams of material.
When the specimen is collected in a vial containing a liquid preservative, the required amount is often indicated by a “fill line” on the container’s label. For a stool culture or a molecular test that looks for the DNA of infectious agents, the specimen must be added until the liquid rises to this specific marking. Do not overfill these preservative-containing vials, as this can affect the chemical balance needed to keep the sample viable for testing. The use of a preservative is essential for maintaining the integrity of delicate structures like parasite cysts or the genetic material of bacteria.
Techniques For Collecting A Clean Sample
Collecting a diagnostically viable stool sample requires specific techniques to ensure the specimen remains clean and uncontaminated by other substances. A primary rule is to avoid mixing the stool with urine or water from the toilet bowl, as these can dilute the sample or introduce substances that interfere with test results. Urinating beforehand is a simple step to prevent this type of contamination.
Most collection kits include a special device, such as a hat-shaped collector that fits under the toilet seat, or instructions to use plastic wrap loosely secured across the rim to catch the specimen. Once the stool is passed, the provided spoon or spatula should be used to transfer the required amount into the collection container. If the stool is not uniform, it is best to collect small portions from different areas, especially any parts that appear bloody, watery, or slimy, to provide a comprehensive representation.
After sealing the container tightly, it is necessary to follow any storage instructions, which often involve refrigeration for tests like Clostridium difficile or immediate submission for others. The label must be completed with the patient’s name, the date, and the exact time of collection before the specimen is transported to the laboratory or clinic. Properly securing the lid and placing the container in the provided biohazard bag protects the sample during transit.
Consequences of Insufficient Or Excessive Quantity
Submitting a stool sample that does not meet the specified volume requirements can lead to significant delays in diagnosis and treatment. When a laboratory receives a sample that is too small, it is considered QNS (Quantity Not Sufficient), and the specimen will be rejected for testing. An insufficient amount means there may not be enough material to perform all the necessary analyses or that the sample may not accurately represent the entire bowel movement.
A rejection necessitates the physician ordering a full re-collection, forcing the patient to repeat the entire process and extending the time before a diagnosis can be made. While under-collection is the more frequent issue, submitting an excessively large sample can also be problematic for the laboratory. Overfilling a container, particularly those with liquid preservatives, can compromise the integrity of the specimen. Adhering closely to the fill line or requested quantity ensures the laboratory can process the sample efficiently and deliver timely, accurate results.