The liquid inside a stool sample collection container is a chemical reagent known as a fixative or preservative solution. This solution is included for a specific purpose related to diagnostic accuracy. It is designed to immediately stabilize the biological components of the specimen, ensuring that laboratory results accurately reflect the patient’s condition at the time of collection. Without this preservative, the sample would rapidly degrade, rendering it useless for many types of testing. The exact nature of this liquid depends on the specific diagnostic tests ordered.
Identifying the Preservative Solution
The chemical makeup of the liquid is not standardized across all kits, as the contents are tailored to the intended laboratory analysis. For traditional diagnostic testing for parasites, the liquid is typically a fixative solution like 10% aqueous formalin or a Polyvinyl Alcohol (PVA) preparation. Formalin-based solutions are generally clear and effectively preserve the structure of helminth eggs and larvae for microscopic identification. PVA, often appearing slightly tinted, is useful for preserving the delicate structure of protozoan cysts and trophozoites for permanent stained smears.
Newer, one-vial collection systems often contain proprietary formulations free of mercury and formalin, such as Sodium Acetate-Acetic Acid-Formalin (SAF). SAF is a non-mercury alternative that facilitates both concentration procedures and the creation of permanent stained slides. For molecular diagnostic tests, such as Polymerase Chain Reaction (PCR), the preservative must be compatible with DNA extraction. This leads to the use of specialized buffers that stabilize nucleic acids rather than cell morphology. The liquid is designed to maintain the integrity of the sample until it can be processed in a specialized laboratory.
The Critical Role of Chemical Preservation
As soon as a sample is passed, indigenous bacteria and enzymes begin to break down cellular structures, including any potential pathogens. This degradation process quickly destroys the diagnostic features required for accurate identification. The preservative liquid immediately halts this biological activity. By introducing the sample into a solution that accounts for a ratio of approximately one part stool to three parts preservative, the internal environment of the container is chemically stabilized.
Stabilization preserves pathogen morphology, which is necessary for microscopic examination. Parasites like protozoa exist in two forms: the delicate feeding stage (trophozoite) and the dormant, resistant stage (cyst). Both forms can rapidly lose their characteristic shape outside of the body. The fixative works by chemically cross-linking proteins, effectively “freezing” the organism’s structure for later identification under a microscope. Without this immediate halting of degradation, microscopic features used for species identification would become distorted or unrecognizable, leading to inaccurate diagnoses.
Safe Handling and Disposal Procedures
Because the liquid contains chemicals like formaldehyde, which is a known irritant and suspected carcinogen, the container must be handled carefully. The laboratory pre-fills and seals the container, and you should never attempt to remove the liquid or transfer it. Accidental contact with the skin or eyes requires immediate and thorough washing with running water for at least 15 minutes. Medical attention should be sought if irritation persists.
The correct collection technique involves introducing the stool sample into the container up to the designated fill line, ensuring the preservative liquid is not spilled. After adding the sample, the cap must be tightened securely to prevent leaks during handling and transport. The specimen should then be mixed with the preservative by gently shaking the sealed container. Once collected, the sample is typically sealed within a biohazard bag to contain potential leakage and maintain sanitary conditions during transport. Final disposal of any remaining kit components should follow the specific instructions provided by the testing facility.