Collecting biomaterial for laboratory research often becomes stressful, especially if the procedure is scheduled for early in the morning, and the body “works” according to its own schedule. Many patients wonder whether it is possible to collect the analysis the night before, so as not to suffer from waking up, and how long the biomaterial retains its properties in cold conditions. The answer to this question is not universal: it directly depends on the type of research prescribed by the doctor and the containers used.
Sample freshness is a critical factor for obtaining a reliable result, since irreversible chemical and bacteriological processes begin in feces immediately after defecation. If you plan to take a test for occult blood, eggworm or dysbacteriosis, the storage rules will be significantly different. Violation of the temperature regime or time frame can lead to a false positive or false negative diagnosis, which will require repeated tests and loss of time.
In this article we will analyze in detail, how long can feces stand in the refrigerator for various types of diagnostics, which containers to use and what absolutely cannot be done with biomaterial. Understanding these nuances will help you pass a high-quality test the first time and avoid mistakes in diagnosing diseases of the gastrointestinal tract.
Factors influencing the safety of biomaterial
The main enemy of biomaterial is time and ambient temperature. Immediately after defecation, bacteria begin to actively multiply in the feces, which are normally present in the intestines, but change their activity outside it. Temperature conditions plays a key role: in warmth, the processes of decay and fermentation proceed rapidly, while cold slows down the vital activity of microorganisms. That is why the refrigerator is the only acceptable place for short-term storage.
The second important factor is the type of research. For a coprogram (general analysis), the preservation of physical properties and cellular elements, which can be destroyed under the action of their own enzymes, is important. For analysis of helminth eggs, it is critical that the larvae do not die or, conversely, begin to develop, changing their stage. And when studying for occult blood reagents can react with decay products if the sample is old.
⚠️ Attention: Biomaterial cannot be frozen in a regular freezer! Ice crystals destroy the cellular structure and eggs of parasites, making the sample unsuitable for microscopy. Only cooling in the main chamber of the refrigerator is permissible.
The tightness of the container also affects the safety. If the container is opened or not closed tightly, the sample dries out, and foreign bacteria from the air can get inside, distorting the picture microflora. The use of sterile pharmaceutical containers with a tight lid minimizes these risks compared to food jars or matchboxes, which are prohibited from using.
General rules for collecting and preparing a container
Before discussing the time frame, you need to make sure that the collection is done correctly. Using unsterile containers is a common mistake that ruins all efforts. Household jars may contain traces of detergents or other substances that will react chemically with laboratory reagents. Therefore, for collection it is necessary to use special containers with a spoon, sold in pharmacies. Defecation should take place in a clean, dry container (a vessel, a pot or cling film stretched over the toilet). You cannot collect material directly from the water in the toilet, since the water contains bleach and other impurities, as well as bacteria from the sewer system, which is guaranteed to spoil the result of the analysis for containers with a spoon, sold in pharmacies.
Defecation should occur in a clean, dry container (a vessel, a pot, or cling film stretched over the toilet). You cannot collect material directly from the water in the toilet, as the water contains bleach and other impurities, as well as bacteria from the sewer system, which is guaranteed to spoil the test result. dysbacteriosis or intestinal group.
☑️ Preparation for collecting the analysis
The volume of material also matters. For most studies, a sample the size of a walnut (about 5-10 grams) is sufficient. If too little is collected, the lab technician may not have enough material to perform all the necessary tests. If you have collected too much, this is not a problem, but storing a large volume in a small container is inconvenient, and it can quickly change its properties due to uneven cooling.
Storage periods for different types of analyzes
The time that biomaterial can be in the refrigerator varies depending on the purpose of the study. Below is a table systematizing the acceptable periods for the main types of diagnostics.
| Type of study | Maximum shelf life | Temperature conditions | Features |
|---|---|---|---|
| Coprogram (general) | up to 8 hours | +2...+8 °C | It is advisable to give it fresh |
| For worm eggs | up to 24 hours | +4...+8 °C | Storage for 24 hours is acceptable |
| For hidden blood | up to 6-8 hours | +2...+6 °C | Requires a diet for 3 days |
| For dysbacteriosis | up to 2 hours | Not recommended | Only fresh, without cold* |
| For carbohydrates | up to 6 hours | +2...+8 °C | Strictly liquid part |
Pay attention to the line about dysbacteriosis. For this analysis, the biomaterial must be delivered to the laboratory as quickly as possible, ideally within 30-60 minutes. Cooling can kill some anaerobic bacteria that are sensitive to oxygen and temperature changes, which will lead to an incorrect ratio of microflora in the results.
For analyzes on worm eggs and protozoa the situation is different. Helminth eggs are quite stable in the external environment, but if stored for a long time (more than a day), they can begin to change their structure or, conversely, develop if conditions are favorable. Therefore, the 24 hour rule is limiting, but not desirable. It is better to focus on 8-12 hours.
What to do if you need to keep the sample for longer than a day?
If you do not have time to take the test within the allowed time, you will have to throw it away and collect a new one. Preservatives are not used for home storage, as they distort the chemical composition. The only way out is to find a laboratory with 24/7 operation or reschedule the collection date.
Storage specifics for analysis for eggworm
A fecal test for helminth eggs (eggworm) is one of the most frequently prescribed studies, especially for children before visiting the pool, garden or school. Unlike bacteriological cultures, parasite eggs have a dense shell, which makes them more resistant to external influences. That is why for this type of diagnosis, storage in the refrigerator for up to 24 hours is allowed..
However, there is a nuance associated with the type of parasites. Some protozoa, such as amoebas, become inactive or destroyed in a cold environment, and the laboratory technician may not see them. If the doctor suspects the presence of protozoa, he usually requires the material to be delivered warm within 15-30 minutes. To detect roundworms or pinworms, the time window is wider.
It is important to correctly place the container in the refrigerator. Do not place it on the door, where the temperature fluctuates constantly due to opening, or near the freezer, where there is a risk of freezing the sample. The optimal location is the middle shelf, away from food, to eliminate cross-contamination and foreign odors, although an airtight container should protect the contents.
Nuances for coprogram and hidden blood
Coprogram is a comprehensive study that evaluates the physical, chemical and microscopic properties of feces. Every detail is important here: color, smell, the presence of undigested fibers, leukocytes and red blood cells. During long-term storage, even in the cold, oxidation of pigments occurs (color changes), and leukocytes can be destroyed, which will lead to an erroneous conclusion about the absence of inflammation.
Analysis for occult blood (Gregerson reaction or immunochemical test) requires special care. Blood in the stool is quickly destroyed by bacteria and enzymes (hemoglobin is converted into other compounds). If you collect the material in the evening, and in the morning it sits in the refrigerator for 10 hours, the reaction may be weak or negative, although there is bleeding in the gastrointestinal tract. For this test, the “collected - lucky” rule works best.
⚠️ Attention: Before taking the test for occult blood, you must follow a diet (exclude meat, fish, apples, green vegetables) for 3 days, otherwise the result will be false positive, regardless of the freshness of the sample.
If you still have to store a sample for coprogram, make sure that it does not come into contact with urine. Even a small amount of urine that gets into the container makes the analysis for occult blood and some other indicators uninformative, since urine contains its own salts and cells that distort the picture.
What absolutely cannot be done with the sample
There are a number of common misconceptions and mistakes that patients make when trying to “save” the analysis. First, do not add water, preservatives, or medications to the container. Some people think that formalin or alcohol preserves the sample, but for most modern laboratory methods (especially PCR and enzyme immunoassays) this is unacceptable - the reagents will conflict with the preservative.
Secondly, you cannot leave the container open “for ventilation.” There is a myth that feces must “breathe.” In fact, open access to air leads to the drying of the surface layer and the entry of dust and bacteria. The container must be tightly closed immediately after collecting the material.
Thirdly, you should not use dirty dishes. Even a thoroughly washed and scalded jar of baby food or mayonnaise is not sterile. Residues of grease or detergent may react in chemical tests. Use only pharmaceutical sterile containers.
Frequently asked questions (FAQ)
Is it possible to collect a stool test in the evening if it is not possible in the morning?
Yes, for analysis of worm eggs and coprogram, this is acceptable if you store the container in the refrigerator at a temperature of +2...+8 °C for no more than 8-12 hours (maximum 24 hours for helminths). For analysis of dysbacteriosis and occult blood, evening collection is not recommended.
What to do if a child pooped in a potty, but there is no special container?
You need to carefully, with a clean spoon (can be pre-treated with boiling water), transfer the material into a clean, dry container (for example, a glass jar with a wide neck, scalded with boiling water) and tightly close. But it is better to always have a spare pharmacy container at home.
Is it possible to freeze stool if you need to transport it far?
No, you cannot freeze stool for standard tests (coprogram, oviworm, dysbacteriosis). Ice crystals destroy the structure of parasite cells and eggs. The biomaterial can only be cooled.
Does taking antibiotics affect the result if the feces have been left in the refrigerator?
Antibiotics affect the composition of the microflora in the intestine before defecation. Storing in the refrigerator only slows down the process of composition changes after leaving the body. If you are taking antibiotics, warn your doctor about this, since the analysis for dysbacteriosis during this period will not be informative.
How many grams of feces are needed for analysis?
The optimal volume is about 5-10 grams (about the size of a walnut or 1-2 teaspoons). This quantity is enough to conduct all main types of research.