The situation when it is necessary to collect biomaterial for analysis, but it is not possible to immediately place it in the cold, arises quite often. This may be due to the early awakening of the child, the lack of a sterile container at home, or the sudden cancellation of plans to take tests to the laboratory. It is important to understandthat feces are not just waste, but a complex biological substance in which the processes of change immediately begin after defecation.
Enzymatic activity and proliferation of bacteria can significantly distort the results of laboratory tests, which will lead to an erroneous diagnosis or the need for a retake. Microorganismscontained in the sample, at room temperature, begin to actively change their numbers, which is critical for tests for dysbacteriosis or intestinal group. That is why the question of how to store feces if there is no refrigerator requires a clear and balanced answer based on biochemical processes.
In this article we will analyze the permissible time intervals, ways to slow down the deterioration of the material and the storage features of various types of tests. Temperature conditions is a key factor, but not the only thing: the composition of the nutrient medium in the container, the tightness of the packaging and the time elapsed from the moment of defecation play no less a role. Following the instructions will allow you to avoid false results.
Biochemical processes in biomaterial at room temperature
Immediately after leaving the body, feces are exposed to oxygen and the environment. At this moment bacterial flora, which was in anaerobic conditions of the intestine, begins to actively respond to changes in the environment. The processes of decay and fermentation are accelerated, which leads to a change in the pH, color and smell of the sample.
Particular attention should be paid to enzymes. They continue to break down proteins and carbohydrates even outside the body, unless this process is stopped by cooling or preservation. Leukocytes and red blood cells, the presence of which laboratory technicians often look for, are quickly destroyed at high temperatures, which can lead to a false negative result when diagnosing inflammation.
⚠️ Attention: At temperatures above +20°C, decomposition processes begin within 30-40 minutes. For accurate diagnosis, this is a critical window, after which the sample is considered unsuitable for a number of specific tests.
The rate of change directly depends on the initial state of health of the patient and the composition of his microflora. If putrefactive processes predominate in the intestines, then outside the body the material will deteriorate faster. Preservation in this case, it is the only way to “freeze” biological time and record the state of the microflora at the time of collection.
Acceptable time frames for storage without refrigeration
The time that biomaterial can be outside the refrigeration chamber is strictly regulated for different types of research. For a general analysis of stool (coprogram), a period of up to 2-3 hours is considered acceptable, provided that the room temperature does not exceed +18-20°C. However, this is maximum limit, and the sooner the sample is delivered, the better.
If we are talking about identifying the eggs of worms or protozoa, then the time window narrows. Some types of parasites, when cooled or, conversely, when overheated, change their morphology or are destroyed. Amoebae, for example, in heat they quickly transform into a mobile form, which is difficult to identify in a fixed preparation, or die, which makes the analysis meaningless.
For tests for occult blood, time frames more flexible, since hemoglobin is more stable, but here too long-term storage at room temperature is undesirable. Oxidative processes can change the chemical composition, which will affect the sensitivity of test systems.
Why is time so critical?
Laboratory analyzers are configured to work with fresh material. Long-term storage at room temperature leads to lysis (destruction) of epithelial cells and leukocytes, which makes it impossible to count them under a microscope.
Below is a table showing the dependence of sample suitability on time and type of analysis:
| Type of analysis | Max. time without cold | Risk of distortion | Recommendation |
|---|---|---|---|
| Coprogram (general) | 2-3 hours | Average | Deliver as soon as possible soon |
| Eggs of worms/Protozoa | 1-2 hours | High | Urgent delivery required |
| Occult blood | 4-5 hours | Low | Avoid direct sun |
| Dysbacteriosis (seeding) | 0 minutes (requires cold) | Critical | Only from cold element |
Preservation methods and special containers
If you know in advance that you will not be able to provide cold, the best solution is to use special containers with a preservative. Such containers contain chemicals (usually formaldehyde or alcohol based), which fixed biomaterial. This allows you to store the sample at room temperature for up to 24 hours, and sometimes up to 3-5 days, depending on the composition of the preservative.
Such containers are often used for research on helminth eggs and protozoa. The material in them does not deteriorate, since the preservative stops the activity of bacteria and prevents the destruction of parasites. However, for biochemical analyzes or tests for occult blood, such containers are absolutely not suitableas the chemicals will react with the reagents.
When using a preservative liquid, it is important to strictly follow the instructions: usually it is necessary to fill the container to a certain mark so that the ratio of the volume of feces to the preservative is correct. Violation of proportions can lead to insufficient fixation or, conversely, to excessive damage to the structure of the sample.
Alternative methods of temporary storage
In situations where special preservatives are not available and the refrigerator is temporarily not working or is not available (for example, during camping conditions or during a power outage), you can resort to other methods. One of them is to create a “thermos” effect using cold elements, if it is possible to pre-freeze them.
If there is no cold at all, contact of the sample with heat should be minimized. You can place a hermetically sealed container in a container of cold water (if you have access to a well or deep well where the temperature is consistently low). Earth cellar or a container buried in the shade can also reduce the ambient temperature by several degrees, which will slow down the growth of bacteria.
It is important to avoid direct exposure to sunlight. Ultrafiltration and solar heating can “cook” protein structures in a sample in a matter of minutes. Even in the shade at high ambient temperatures, processes go faster, therefore it is critically important to reduce transportation time to a minimum.
Features of collection for different types of tests
Different studies have their own requirements for the sample. For analysis, not only time is important, but also diet before delivery, but if we talk about storage, the main thing here is to avoid oxidation. The container must be tightly closed, air access is limited. occult blood Not only time is important, but also diet before donation, but if we talk about storage, the main thing here is to avoid oxidation. The container must be tightly closed, air access limited.
When examining dysbacteriosis the situation is the most difficult. This test requires culture of live bacteria. At room temperature, some types of bacteria begin to die, while others actively multiply, changing the ratio of flora. Therefore, for dysbacteriosis, storage without cold is practically impossible, unless a special transport medium is used (for example, Amies or Stuart), which maintains the viability of microorganisms.
For coprogram (general analysis), the requirements are a little softer. Here, mainly undigested food remains, mucus, blood and basic indicators are assessed. However, here too, long-term storage will lead to a change in color (oxidation of bilirubin) and the appearance of a specific odor, which can confuse the laboratory technician.
⚠️ Attention: Never freeze feces in a regular freezer unless specifically instructed by a doctor. Ice crystals destroy cellular structures, making the sample unsuitable for microscopy.
Rules for transporting biomaterial
Transportation is the final stage, which also has its own rules. Even if you were able to keep a sample at home, it may get damaged while traveling. In the summer, the temperature in the car quickly rises above +30°C, turning the container into an incubator for bacteria.
Use thermal bags or cooler bags for transportation. Even a simple bag with a few ice cubes (wrapped in a cloth so as not to directly overcool the sample) will help buy time. Sealing Packaging is required: foreign odors or leakage can contaminate the sample or the environment.
If you are transporting material in winter, it is necessary on the contrary, protect from freezing. Although low temperature preserves, complete freezing of a sample in a glass or plastic container can lead to rupture of the container or irreversible changes in the structure. It is optimal to keep the container in the inner pocket of clothing, using body heat to maintain a positive temperature.
☑️ Ready for transportation
Frequent errors during collection and storage
One of the most common mistakes is collecting material from the surface of a toilet bowl or from a pot that has not been treated. Disinfectants, the remnants of washing powders or bleach, getting into the feces, kill microflora and destroy epithelial cells. This is guaranteed to lead to a false result.
Another mistake is collecting material in the evening for morning delivery if the container does not contain a preservative. Overnight at room temperature, enormous changes occur in the sample. The bacterial composition changes so much that analysis for dysbiosis or intestinal group becomes meaningless.
Also, patients often forget to label the container. The laboratory accepts hundreds of samples, and if there is no data on the jar, it can simply be thrown away or mixed up. Labelling Must contain the name, date and time of collection.
FAQ: Frequently asked questions
Can feces be stored in the refrigerator without a preservative?
Yes, for general analysis (coprogram) and analysis for worm eggs, storage in the refrigerator at a temperature +2...+4°C is allowed for 8-12 hours (maximum up to 24 hours, but with loss of quality). For analysis of dysbacteriosis, storage without a preservative is not recommended, even in the cold, since aerobic flora begins to grow.
What to do if a child went to the potty at night?
If there is little time left until the morning (3-4 hours), you can leave the potty in a cool place (not on the radiator!). In the morning, carefully collect the material with a spoon from different places (top, side, inside) into a sterile container. If more than 6 hours have passed, the material is most likely no longer informative.
Does urine affect the result?
Yes, urine can wash away white blood cells or red blood cells, and also change the chemical composition of stool (for example, pH). You need to collect feces in a dry, clean container, excluding urine and water from the toilet.
How long can feces be stored for occult blood?
At room temperature - no more than 3-4 hours. Refrigerate for up to 24 hours. However, modern immunochemical tests (iFOBT) often require strict adherence to the temperature regime specified in the instructions for a specific kit.