Collecting biomaterial for laboratory research often raises questions, especially when the procedure falls in the evening. Many patients wonder if it is acceptable to leave the sample container in the refrigerator until their morning clinic visit. The correct approach to this process directly affects the accuracy of diagnosis and eliminates the need to repeat the analysis.
It is important to understand that feces are an active biological medium where fermentation processes and bacterial activity continue even after defecation. Temperature violation or exceeding the permissible storage time can lead to distorted results, which will lead to an incorrect diagnosis. In this article, we will examine in detail the permissible time intervals and conditions for storing samples.
General principles for preserving biomaterial
The main purpose of placing biomaterial in the cold is to slow down the metabolic processes of bacteria inhabiting the intestines. At room temperature, the microflora continues to actively multiply, which changes the quantitative ratio of microorganisms. Cooling allows you to preserve the state of the sample, bringing it as close as possible to the moment of defecation.
However, not all types of analyzes allow long-term storage. Some studies require exclusively fresh material, since certain types of protozoa or enzymes are quickly destroyed or modified under the influence of cold. Laboratory assistants it is always recommended to submit the material in the morning, immediately after collection.
If this is not possible, it is necessary to strictly observe the temperature regime. The optimal range is considered to be from +2 to +8 degrees Celsius. This is the standard temperature on the shelf of a home refrigerator, not in the freezer. Freezing the sample is strictly prohibited, since ice crystals destroy cellular structures.
Storage periods for different types of tests
Time during which the biomaterial remains suitable for research depends on which parameters will be studied in the laboratory. Universal period there is no diagnostic for all types, and ignoring these differences can reduce the effectiveness of the study to zero.
For a standard coprogram (general analysis), storage in the refrigerator for 8–10 hours is permissible. At this time, the physicochemical properties of feces remain stable. If it is necessary to identify eggs of helminths or protozoa, the time frame can be reduced, since vegetative forms of protozoa quickly die when cooled.
| Type of research | Maximum shelf life | Temperature conditions | Acceptability storage |
|---|---|---|---|
| Coprogram (general analysis) | 8–10 hours | +2...+8 °C | Acceptable |
| Eggworm analysis | 5–8 hours | +2...+8 °C | Acceptable restrictions |
| Occult blood | Up to 6 hours | +2...+8 °C | Fresh is recommended |
| Bacterial culture | Not stored | Only fresh | Prohibited |
| Analysis for dysbacteriosis | Not stored | Only fresh | Prohibited |
Analysis requires special attention on occult blood and bacteriological cultures. In the first case, chemical reactions can change the color of the reagents, in the second, third-party microflora from the air or container can distort the picture of the growth of pathogenic bacteria. For such tests, the material must be delivered to the laboratory within 1-2 hours.
Rules for container preparation and collection
Hygiene of the collection procedure plays no less a role than transportation conditions. Using unsuitable containers may result in contamination of the sample. Modern pharmacy containers are made of inert plastic that does not react with biomaterial.
Before collection, you need to prepare a clean, dry vessel or stretch a clean plastic film over the toilet. Do not allow urine or toilet water to enter the sample, as this will change the chemical composition and may destroy some microorganisms. Sterility The outer surface of the container is also important to prevent the entry of foreign bacteria.
The volume of material should be comparable to the size of a walnut or about 5-10 grams For loose stools, 2–5 ml is enough. The container must be tightly closed immediately after collecting the sample to prevent drying and oxidation. Plastic spoon, built into the lid, is convenient for collecting samples from different places.
☑️ Rules for collecting biomaterial
⚠️ Attention: Do not use matchboxes, paper bags or household food containers to collect the analysis. They are not sterile and may contain residue from detergents or previous products, which will lead to false positive results.
Temperature conditions and place in the refrigerator
Where exactly should you put the container in the refrigerator? This is not an idle question, since temperature zones inside household appliances can vary. The refrigerator door is the least suitable place due to frequent temperature changes when opening.
The optimal place is the middle shelf or vegetable compartment, where the temperature is most stable. It is important to avoid proximity to food products, especially those that are not heat-treated. Cross contamination Bacteria from the refrigerator can affect the results of bacteriological testing.
It should be remembered that a household refrigerator is not intended for storing biological materials, so maintaining hygiene inside the chamber is critical. If open foods are stored in the refrigerator, it is better to place the container with the analysis in an additional sealed bag. This will create a barrier and protect the sample from foreign odors and microorganisms.
What to do if it is not possible to use a refrigerator?
If cold storage is not possible (for example, on the road), the shelf life of the material is reduced to 1-2 hours at room temperature. In the hot season, this interval is reduced to 30-40 minutes. In such cases, it is better to collect the material immediately before leaving or use the services of a laboratory that provides containers with a preservative.
Features of collection in children and infants
Collecting analysis in infants is a separate task, since it is difficult to predict the moment of defecation, and the consistency of the stool is often liquid. For infants, special urine bags or sterile bags are used, which are attached to the skin around the anus.
If a child goes to the potty, the container should be thoroughly washed and scalded with boiling water. The use of chemical detergents is unacceptable, since their residues may react with laboratory reagents. Liquid stool Collect from infants using a pipette or syringe without a needle, transferring to a container.
Shelf life for children's tests is the same as for adults, but due to the high speed metabolism in children, fermentation processes in the sample may be more active. Therefore, try to minimize the time between collection and delivery. To analyze for carbohydrates (lactase deficiency), the material must be exclusively fresh.
Frequent errors during storage and transportation
One of the most common mistakes is freezing the material. Patients mistakenly believe that a freezer will preserve the specimen better than conventional refrigeration. In fact, freezing destroys the cell walls of bacteria and protozoa, making the analysis meaningless.
Another mistake is using dirty containers. Even a visually clean jar of mayonnaise may contain traces of fat or detergent. Chemical impurities able to block reactions used by laboratory technicians to identify pathologies. Always use only specialized pharmaceutical containers.
Transportation during the hot season also requires attention. If you are carrying a container in a bag, make sure it does not become hot from the sun or body heat. You can use a thermal bag with a cold element, but do not allow direct contact of the container with ice to prevent local freezing.
⚠️ Attention: Do not leave the container with biomaterial on the windowsill or near heating devices, even for a short time. Sharp heating will accelerate the breakdown of biological components and the proliferation of bacteria.
Use of preservatives and special containers
For some types of research, such as complex analysis for dysbacteriosis or identification of specific antigens, conventional cooling may not be sufficient. In such cases, laboratories give patients containers with preservative solution already added. Such solutions (for example, formaldehyde or alcohol-containing liquids) fix the material, stopping all biological processes. This allows you to store the sample for up to 24 hours and even transport it by mail. However, for general analysis and coprogram, preservatives are not used, since they change the appearance and chemical properties of feces. preservative solution.
Such solutions (for example, formalin or alcohol-containing liquids) fix the material, stopping all biological processes. This allows you to store the sample for up to 24 hours and even transport it by mail. However, for general analysis and coprograms, preservatives are not used, as they change the appearance and chemical properties of feces.
If you are given a container with a preservative, strictly follow the filling instructions: usually you need to fill the container to a certain mark. Exceeding the volume will lead to insufficient concentration of the preservative, and a smaller volume will lead to its excess, which will also distort the results. Special lids with a spoon often already contain the required amount of fixative.
Frequently asked questions (FAQ)
Is it possible to take a stool test if it has been in the refrigerator overnight?
Yes, for general analysis (coprogram) and search for helminth eggs, storage overnight (8-10 hours) at a temperature of +2...+6°C is acceptable. However, for tests for hidden blood, dysbiosis or protozoa, such material will no longer be suitable and will be rejected by the laboratory assistant.
What to do if the stool turns out to be liquid?
Liquid stool can be collected using a pipette or syringe (without a needle) directly from a vessel or from a clean oilcloth. The volume should be at least 5 ml (about one teaspoon). Liquid stool should be stored in the refrigerator with extreme caution, since fermentation processes occur faster in it.
Does taking antibiotics affect the result if the material was stored in the cold?
Taking antibiotics affects the composition of the microflora, regardless of the storage conditions of the material. However, if you are being tested for dysbacteriosis, then storage in the refrigerator is unacceptable even for a short time, since sensitive bacteria may die and the result will be false negative.
Is it possible to freeze feces for analysis?
Absolutely not. Freezing destroys the cellular structure of microorganisms, worm eggs and blood cells. After defrosting, the biomaterial becomes unsuitable for any type of laboratory diagnostics.