Collecting biomaterial for laboratory research often becomes a cause of stress, especially when it comes to time. Many people mistakenly believe that, having collected an analysis in the evening, they can safely take it to the laboratory in the morning, relying on the cold temperature inside the household unit. However biological processes inside the sample they continue to flow even at low temperatures, although much more slowly. It is critically important to understand that the accuracy of the diagnosis directly depends on the freshness of the material, and not just on the conditions of its detention.
The question of how long stool is stored for analysis in the refrigerator does not have a single universal answer, since much depends on the type of research being carried out. Standard time frames established by medical protocols may vary depending on whether laboratory technicians are looking for helminth eggs, occult blood, or dysbacteriosis. Freezing biomaterial is strictly prohibited, since ice crystals destroy the cellular structures of bacteria and change the morphology of parasites, making the analysis useless.
In this article we will analyze in detail the time frames for various types of diagnostics, explain the physiological reasons for the restrictions and give clear packaging instructions. Compliance with these rules will avoid false negative results and the need for a repeated, often unpleasant, collection procedure. Remember that laboratory diagnostics requires strict adherence to regulations, and neglecting storage time can cost you time and money.
The influence of temperature on the safety of biomaterial
The main purpose of placing the container with the sample in a cold place is to inhibition of the vital activity of microorganisms. At room temperature, bacteria begin to actively multiply, and the enzymes contained in the biomass initiate decay processes. This leads to changes in the chemical composition, pH of the medium and cell morphology, which makes the results clinical analysis unreliable. The refrigerator compartment creates conditions under which metabolic processes slow down, but do not stop completely.
The temperature inside a household refrigerator usually ranges from +2 to +6 degrees Celsius. This is the optimal area for short-term canning, but not for long-term storage. If you place the container too close to the back wall, where temperatures can drop below freezing, there is a risk of the edges of the sample partially freezing. On the contrary, storing on the door, where the temperature fluctuates every time it is opened, will not provide the necessary stability for biological samples.
⚠️ Attention: Never store a container with biomaterial in the freezer. Freezing leads to lysis (destruction) of epithelial cells and bacteria, which makes microscopy and bacteriological culture impossible. The result of such an analysis will be erroneous.
It is also important to consider that different components of feces cool at different rates. Dense particles can retain heat longer, creating zones inside the container with a favorable temperature for bacteria to grow, even in the refrigerator. That is why the volume of collected material should not be excessive, and the container itself should be sealed to prevent the entry of foreign odors and condensation, which can affect the chemical composition of the samples. chemical composition samples.
Shelf life for various types analyzes
The time interval during which the biomaterial remains suitable for research is strictly regulated and depends on the purpose of the diagnosis. For the standard coprogram, which assesses the digestive capacity of the gastrointestinal tract, the timing is the most flexible, but still limited. In the case of detection of hidden blood or parasitic infestations, the requirements become more stringent, since the objects being sought can quickly degrade or, conversely, become active.
Below is a table showing the maximum storage time for various types of studies, provided they are kept in a refrigerator:
| Type of analysis | Maximum period (refrigerator) | Optimal period | Risks if exceeded |
|---|---|---|---|
| Coprogram (general) | up to 8-10 hours | 2-4 hours | Change in pH, bacterial growth |
| Eggs of worms (helminths) | up to 5-8 hours | immediately after collection | Destruction of egg shells |
| Hidden blood | up to 6 hours | 3-4 hours | False positive result |
| Dysbacteriosis (bacteriosis) | no more than 3 hours | 1-2 hours | Death of anaerobes, growth of flora |
Particular attention should be paid to the analysis of dysbacteriosis. In this case, we are dealing with live cultures of bacteria that are extremely sensitive to environmental conditions. Even short-term storage in the refrigerator can change the microflora ratio, as aerobic bacteria can begin to suppress anaerobic ones. Therefore, for this type of diagnosis, the rule “the faster, the better” is an absolute priority.
When examining worm eggs worm eggs and protozoa, time also plays a critical role. Some types of protozoan cysts outside the host body quickly lose their specific shape, which makes them difficult to identify under a microscope. Giardia, for example, in a cold environment can shrink and become unrecognizable, which will lead to a false negative conclusion from a laboratory technician.
Rules for collecting and packaging a sample
The quality of the analysis begins with correct collection. The use of sterile containers sold in pharmacies is mandatory. Glass jars of baby food or mayonnaise, even thoroughly washed, may contain microparticles of detergents or organic residues that will distort biochemical parameters. A plastic medical container is chemically inert and guaranteed to be clean. biochemical parameters. The plastic medical container is chemically inert and guaranteed to be clean.
The defecation process should take place in a clean container (for example, in a vessel treated with boiling water or on a plastic film stretched over the toilet) to prevent urine or water from entering the tank. Urine contains harsh chemicals that can destroy the structure of feces. After collection, the material is carefully transferred into the container with a special spoon built into the lid.
☑️ Rules for collecting biomaterial
The volume of collected material also matters. For most tests, an amount equal to one to two teaspoons (about 5-10 grams) is sufficient. Excessive amount of biomass in a closed container creates a thermos effect, making it difficult for the room to cool quickly and evenly. This can lead to the fact that the decay processes inside the lump will proceed faster than on the surface. refrigerator compartment. This can lead to the fact that decay processes inside the lump will proceed faster than on the surface.
After placing the material in the container, it must be tightly closed and placed in the refrigerator as soon as possible. Do not hold the container in your hands or leave it on the table to “ventilate”. Every extra minute at room temperature reduces the likelihood of getting an accurate result. If you plan to take the test in the morning, collect it late in the evening, but strictly adhere to the time frame described in the previous section.
Features of storing the test in children and infants
Collecting biomaterial from young children often turns into a quest, since it is difficult to predict the moment of defecation. Parents often wonder: is it possible to collect stool from a child in the evening in order to take it to the laboratory in the morning? The answer depends on the age of the child and the type of test. For breastfed infants, stool has a more liquid consistency and contains active enzymes, which accelerates the processes of structure change.
If the child goes to the potty, it is easier to collect the material. It is important to use a clean pot, washed with soap and rinsed with boiling water. You should not scrape material from the surface of the pot unless it is perfectly clean, as this may introduce foreign microflora. For infants who are not yet sitting, special urinals or sterile bags attached to the perineum are used.
⚠️ Attention: For children under one year of age, the storage period of the biomaterial should be as short as possible. A baby's liquid stool contains a large amount of moisture and active bacteria, which, when stored in the refrigerator, can change their properties within 3-4 hours. Try to deliver the sample to the laboratory within 2 hours.
When collecting an analysis for carbohydrates or dysbacteriosis in children, the time factor becomes decisive. Enzymes that break down carbohydrates continue to work even in the cold, although more slowly. Therefore, if you collected the material in the evening and take it in the morning, the result may show a false increase in the level of carbohydrates due to ongoing breakdown.
What to do if the child pooped at night?
If defecation occurred late at night (for example, at 2-3 o'clock), and you plan to take the analysis to 8-9 am, such material is most likely no longer suitable for accurate diagnosis, especially for dysbacteriosis. It is better to skip this collection and try to collect the material during the day, delivering it to the laboratory within 1-2 hours. For analysis of worm eggs, overnight collection is acceptable if stored in the refrigerator, but no more than 6-8 hours.
Transportation: how to get it to the laboratory
Even if you correctly collected and stored the material at home, the transportation stage can ruin everything. In summer, when the weather is hot, or in winter, when temperatures are extremely low, delivery conditions become critical. A regular bag will not provide thermal stability. To transport biomaterial, it is recommended to use small cooler bags or thermal containers with refrigerants (cold accumulators).
If you are carrying the analysis in winter on public transport or in a personal car, make sure that the container does not get too cold. Keeping a sample at a temperature below 0 degrees during transportation is tantamount to freezing, which is unacceptable. In the hot season, on the contrary, it is important to prevent heating above +8...+10 degrees, as this will trigger the rapid growth of bacterial flora.
The container must be in a vertical position so that the contents do not spill and stain the lid, which will make it difficult to open it in the laboratory and create a risk of laboratory technician contact with the biomaterial. It is best to place the container in an additional plastic bag for secondary insulation.
Frequent errors and myths about storage
There are many misconceptions that exist among patients. One of the most common myths is that if the test has been left in the refrigerator for two days, nothing bad will happen to it, because “the cold preserves it.” This is a dangerous misconception. Preservation in a medical sense, it requires special chemical reagents, and not just low temperature. Two days of storage make the sample unsuitable for almost any type of diagnosis.
Another mistake is adding water to dry stool to soften it before analysis. This is strictly forbidden. Water changes the concentration of substances, washes away the surface layer where the maximum number of parasite eggs can be contained, and introduces foreign microflora from the water supply. If the stool is very hard, the laboratory itself will carry out the necessary manipulations or ask you to retake the test.
Also, patients often ignore the diet before taking the occult blood test, believing that storage in the refrigerator will neutralize the effect of the meat eaten. This is wrong. Hemoglobin that enters the intestines with food can give a false positive reaction, and cold is not a help here. Preparation for analysis begins 2-3 days before collection, and not when the container is placed in the refrigerator.
Questions and answers (FAQ)
Is it possible to store feces for analysis in the freezer if there is no space in the refrigerator?
No, absolutely not. Freezing destroys the cellular structures of bacteria, protozoa and helminth eggs. After defrosting, the material turns into a heterogeneous mass, unsuitable for microscopy and bacterial culture. The result of such a study will be false.
What should I do if I did not have time to take the test within 8 hours?
If more than 8-10 hours have passed (for coprogram) or 3-4 hours (for dysbacteriosis), the material is considered spoiled. There is no point in submitting it, since the laboratory will either refuse to accept it or give an incorrect result. It is necessary to collect a fresh sample.
Does the shelf life affect whether the stool is liquid or formed?
Yes, it does. Loose stool (diarrhea) contains more water and active enzymes, and the processes in it proceed faster. It is advisable to deliver such material to the laboratory within 1-2 hours. Decorated stool can retain its properties a little longer, up to 6-8 hours in the refrigerator.
Do you need to sign the container before putting it in the refrigerator?
Yes, this is a mandatory requirement. The patient's name and, preferably, the time of collection should be indicated on the container or on the referral. This will eliminate confusion, especially if several family members are taking tests, and will help the laboratory technician assess the freshness of the sample.
Is it possible to collect the test on Friday evening in order to take it on Monday?
No, such a shelf life (about 48 hours or more) is unacceptable for any type of stool analysis. The biological changes will be too great. The analysis must be collected either on the day of delivery, or late in the evening the day before (only for some types of studies and only if delivered early in the morning).