Collecting biomaterial for laboratory research is a procedure that requires strict adherence to a time frame. Often patients are faced with a situation where they need to collect a sample in the evening, but submit it to the laboratory only in the morning of the next day. In such cases, the only safe way to preserve the properties of the biomaterial is proper cooling.
Violation of the temperature regime or exceeding the permissible storage time leads to a change in the chemical composition and structure of the sample. Enzymes contained in the digestive tract continue to act even after defecation, destroying cells and changing the pH of the environment. That is why the question of how long feces can be stored in the refrigerator is critical for making an accurate diagnosis.
In this article we will analyze all the nuances of preserving biomaterial in household appliances. You will learn how temperature affects different types of analyses, which containers are best to use and what absolutely should not be done. Following these simple rules will allow you to avoid repeated tests and get a reliable result the first time.
Factors influencing the safety of biomaterial
The main enemy of biomaterial is time. Immediately after defecation, irreversible processes begin in the sample. Bacterial flora, located in the intestines, is active outside the body. At room temperature, microorganisms begin to multiply rapidly, which distorts the results of microbiological research and coprograms.
Temperature plays a decisive role. Cooling slows down bacterial metabolic processes and enzyme activity, but does not stop them completely. Therefore, even in the refrigerator there are strict time limits. For most standard tests, the upper storage limit is 8–12 hours, but for some specific tests this period is reduced to 2–3 hours.
⚠️ Attention: Freezing stool in the freezer is strictly prohibited! Ice crystals destroy the cell walls of bacteria and protozoa, making the sample unsuitable for microscopy and bacterial culture.
It is important to consider the type of container. The use of household containers (matchboxes, yogurt jars) is unacceptable due to the risk of contamination by foreign microorganisms. Sterile containers with a spoon ensure tightness and keep the sample unchanged. The tightness of the lid also affects the safety: the access of oxygen can change the redox reactions inside the sample.
Why can’t you use ordinary dishes?
In household dishes there may be traces of detergents that kill bacteria or react with reagents. In addition, glass or plastic in ordinary containers are not sterile, which leads to the growth of foreign microflora and false-positive results.
Storage periods for various types of tests
The answer to the question of how long biomaterial can be stored directly depends on the purpose of the study. Different tests require different conditions, and there is no universal deadline for all tests. Let's look at the main areas of laboratory diagnostics.
For coprograms (general stool analysis), storage in the refrigerator at a temperature of +2 to +8 degrees Celsius for 8–10 hours is permissible. During this time, the main physical and chemical indicators (color, shape, presence of mucus or blood) remain stable. However, the microscopic picture may begin to change after 6 hours.
The situation with bacteriological culture (analysis for dysbacteriosis, intestinal group) is much stricter. The ideal option here is to deliver the material to the laboratory within 2 hours (maximum 3 hours) after defecation. If this is not possible, some transport media allow you to increase the period to 6–8 hours, but the reliability of the result is reduced.
Research it Eggs of worms and protozoa is also time sensitive. Helminth larvae can develop or collapse, and protozoa (for example, Giardia) turn into cysts or die when they cool, which makes them difficult to detect under a microscope. The maximum storage period for this type of analysis should not exceed 6–8 hours.
Below is a table systematizing data on the shelf life of biomaterial in the refrigerator:
| Type of analysis | Maximum period (refrigerator) | Temperature mode | Delivery priority |
|---|---|---|---|
| Coprogram (general) | 8–10 hours | +2..+8 °C | High |
| Bacteriosis (dysbacteriosis) | 2–3 hours (up to 6 with a preservative) | +2..+8 °C | Critical |
| Eggs of worms / Protozoa | 6–8 hours | +2..+8 °C | High |
| Occult blood | 3–4 hours | +2..+8 °C | Critical |
Rules for collecting and packaging the sample
The quality of the result depends not only on how long you stored the sample, but also on how you put it together. Violation of the collection technique can negate all efforts to maintain the temperature regime. The first step is preparation.
Defecation should occur in a clean, dry container. Do not collect material from the surface of the water in the toilet bowl, as the water may contain disinfectants or foreign bacteria. It is best to use a dry vessel treated with boiling water, or stretch clean cling film over the toilet seat (if the design allows it).
To collect the material, use a special spoon built into the lid of a sterile container. The volume of the sample should be approximately the size of a walnut (or 1-2 teaspoons). If the stool is liquid, it is pipetted in an amount of about 2 ml.
☑️ Correct collection of material
After collecting the container, it is necessary close hermetically. This will prevent the sample from drying out and causing odor to spread. The container must indicate the patient's name and surname and the time of collection of the material. It is better to glue the label on the plastic itself, and not on the lid, so as not to confuse the samples if there are several of them.
Technical nuances of storage in the refrigerator
Where exactly in the refrigerator should the container with biomaterial be stored? This is not an idle question. On door shelves, the temperature often fluctuates due to frequent opening, creating unfavorable conditions for the sample. The optimal place is the middle shelf of the main compartment, in the back, away from the walls (so that the material does not freeze) and from the door.
It is necessary to isolate the container from food. Even when closed, biomaterial is a potential source of pathogenic flora. It is recommended to place the container in a separate, clean plastic bag or plastic tray with a lid. This will create an additional barrier and protect the products from possible contamination, and the sample from foreign odors.
⚠️ Attention: Make sure that the temperature in the selected compartment of the refrigerator is stable. Do not place the container near the No Frost system, where cold air currents could locally freeze the sample, or against the back wall where condensation may form.
If you are using a refrigerator with Zone Fresh or similar meat/fish zones where the temperature is close to 0°C, it may be too cold for some types of analysis (risk of partial freezing). It is better to stick to the standard cooling zone (+4°C).
Frequent errors when storing feces
Even knowing the theoretical fundamentals, patients often make practical mistakes that lead to defective material. The most common is storing at room temperature overnight. Many people mistakenly believe that if you close the jar with a lid, then nothing will happen in 8-10 hours in the heat. This is not so: the processes of rotting and fermentation are active.
The second mistake is using unsterile containers. Residues of food, detergents, or simply microflora from the walls of an ordinary jar can give rise to the growth of colonies that were not in the intestines. As a result, the analysis will show dysbacteriosis where it is not, or, conversely, will hide the real problem.
The third mistake is failure to maintain tightness. If the lid is not closed completely, the sample dries out. The density of feces changes, which distorts the results of the coprogram. In addition, drying leads to a concentration of substances, which can give a false positive reaction to occult blood.
The fourth mistake is storing longer than expected “just in case.” Some patients think: “If it stays in the refrigerator for another day, nothing will happen.” Biological material is not canned food. After 24 hours in the refrigerator, the cell structure is destroyed so much that the laboratory technician will not be able to carry out diagnostics.
Storage specifics for children and infants
Collecting analysis from young children has its own characteristics, but the storage rules remain the same. For infants, special urine bags or sterile gas outlet tubes are often used to collect liquid stool.
If a child uses the potty, the potty should be thoroughly washed with soap, rinsed with boiling water and dried before use. You cannot collect material from a diaper or diaper, since the absorbent layer will instantly take away the liquid fraction, leaving only dense particles, which will distort the result.
The shelf life of children's biomaterial is the same: a maximum of 8 hours for general analysis and 2-3 hours for sowing. However, parents should be especially attentive to the temperature: in the refrigerator with baby food, the container should be kept separately, in a bag.
⚠️ Attention: If the child has loose, watery stools (diarrhea), the time for delivery of the material to the laboratory is reduced. Such a sample loses its properties faster, and it is advisable to bring it “warm” (within 1 hour).
If it is impossible to collect the material in the morning (the child goes to the toilet only in the evening), discuss with your doctor the possibility of using special preservatives. Some laboratories provide containers with fixing liquids that allow you to store the sample for up to 24-48 hours, but only for certain types of research (for example, for helminth eggs).
What to do if the shelf life has expired?
If you find that you forgot to put the container in the refrigerator or more than 12 hours have passed since collection, this material cannot be used. The results will be unreliable, and the doctor may make an incorrect diagnosis or miss a serious disease.
The only correct decision in such a situation is to throw away the damaged sample and collect a new one. Yes, it is unpleasant and takes time, but health is more important. Trying to pass “old” material is a waste of money for analysis and the doctor’s time.
If the situation repeats (the child does not go to the toilet in the morning, or there is no way to quickly get to the laboratory), contact the laboratory in advance. You may be offered alternative diagnostic methods or given containers with preservatives that increase the life of the sample.
Is it possible to add water if the stool is dry?
No, absolutely not. Adding water, saline or any other liquid completely changes the concentration of substances and osmotic pressure, making the analysis meaningless.
FAQ: Frequently asked questions
Is it possible to store feces in the freezer if there is no space in the refrigerator?
No, you cannot freeze feces. When water freezes, it expands and forms crystals that destroy the cell walls of bacteria, protozoa, and epithelial cells. After defrosting, you will receive a homogeneous mass, unsuitable for microscopy and sowing.
What to do if the light in the refrigerator was turned off at night?
If the refrigerator was not opened, the temperature inside could remain for several hours. However, if you are not sure that the temperature was kept within +2..+8 °C, it is not worth the risk. It is better to retake the test than to get a false result.
Does the fact that the container was placed next to garlic or fish affect the analysis?
With a hermetically sealed lid, odors will not have a direct effect on the chemical composition of feces. However, if the lid was not closed tightly, the sample could have absorbed volatile substances, which could theoretically affect organoleptic properties (odor), although this is secondary for laboratory tests. The main thing is tightness.
How long can you carry the analysis in a cooler bag?
In a special cooler bag with cold elements (cold accumulators), biomaterial can be transported for up to 3-4 hours. It is important that the container does not come into direct contact with the ice element to avoid localized freezing. Use a layer of fabric or paper.
Do you need to heat the stool before donating if it was in the refrigerator?
No, you cannot heat the sample (on a radiator, in a microwave or hot water). A sharp change in temperature will kill beneficial microflora (during sowing) and change the structure. The sample is submitted in the form in which it was stored (refrigerated). The laboratory itself will bring it to the desired temperature if necessary.