Collection biological material for laboratory research - this is a critical stage on which the accuracy of the diagnosis directly depends. Often patients are faced with a situation where it is necessary to collect a test in the evening and submit it to the laboratory in the morning, or they need to collect material from a child who goes to the toilet on an unpredictable schedule. In such cases, the critical question arises about how long and under what conditions it is permissible to store the sample before delivery to the clinic. Errors at this stage can lead to false-positive or false-negative results, which will lead to unnecessary treatment or, conversely, the omission of a serious disease.
Modern medicine places high demands on the quality of biomaterials. Feces are a breeding ground for many bacteria, and fermentation processes in them begin almost immediately after defecation. Temperature change, oxygen availability and time are three factors that dramatically change the composition of the sample. If you plan to postpone the test, you need to clearly understand what kind of research will be carried out, since different tests have their own strictly regulated time intervals.
In this article we will analyze in detail the permissible storage periods for various types of tests, the influence of the temperature of the refrigeration chamber and the features of using special preservatives. You will learn why you should not freeze material, how to package it correctly, and what to do if delivery time has expired. Compliance with these rules will help you avoid repeated tests and provide the doctor with a reliable picture of your health.
General principles and temperature conditions
The basic rule that every patient should remember is: the fresher the material, the more accurate the result. However, the realities of life dictate their own conditions, and the ideal situation of “collecting and immediately carrying” is not always possible. Under standard conditions, at room temperature, the processes of decay and reproduction of microflora occur very quickly. After just 3-4 hours, the composition of stool may change so much that the laboratory refuses to accept it or produces incorrect data.
Cooling is used to slow down these processes. The optimal temperature for storing most biological samples is between +2 and +6 degrees Celsius. These are the conditions provided by the standard fridge compartment of a household refrigerator. It is important to understand that we are talking specifically about the middle shelf, but not about the freezer compartment and not about the door, where the temperature constantly fluctuates when opening. Temperature conditions is a key factor that preserves the structure of cells and the composition of bacteria.
However, even in the refrigerator, time does not stop. Enzymatic activity does not stop completely, but only slows down. Therefore, there is a strict time limit: in most cases, the material should not be stored for more than 8-12 hours. For some types of research this period is even shorter. If you are not sure of the exact time of collection, it is better to play it safe and collect a fresh portion than to risk the accuracy of the diagnosis.
⚠️ Attention: Never leave a container with biomaterial on the table at room temperature for more than 3-4 hours. A warm environment accelerates the proliferation of pathogenic flora, which can distort the results of bacteriological culture.
When placing the container in the refrigerator, make sure that it is tightly closed. This will prevent foreign odors and fumes from entering and also protect other products from potential contamination. Use sealed containers that are sold in pharmacies, as they are specially designed for this purpose and provide the necessary insulation.
Storage periods for various types of tests
There is no single standard for all types of research. The requirements for the biomaterial depend on what exactly the laboratory technician is looking for: helminth eggs, occult blood, bacteria or chemical composition. It is a mistake to believe that if stool looks normal, then it is suitable for any analysis. Let's look at the main groups of studies and their specific requirements.
For analysis for worm eggs (helminthiasis) and the simplest requirements are the most stringent in terms of freshness, unless preservatives are used. In warm feces, the eggs of some types of helminths can begin to develop or, conversely, collapse, making them invisible under a microscope. The maximum shelf life of such material in the refrigerator is 8 hours. If you do not have time to deliver the analysis within this period, the result may be false negative.
The situation is different with the analysis for occult blood. The most important thing here is diet and the absence of bleeding factors (for example, brushing teeth) before collection. You can store such a sample in the refrigerator for up to 12 hours, but up to 6 hours is considered optimal. Long-term storage can lead to oxidation of hemoglobin, which will complicate the chemical reaction.
The most sensitive is bacteriological culture (bacteria culture). The purpose of this test is to identify living bacteria and determine their sensitivity to antibiotics. Any change in temperature or storage time changes the ratio of microorganisms: some die, others begin to actively reproduce. For bacterial culture, it is advisable to deliver the material to the laboratory within 2-3 hours. As a last resort, storage in the refrigerator for up to 6 hours is allowed, but the reliability of the result is reduced.
☑️ Check before analysis
The influence of preservatives on the shelf life
There is a way to significantly extend the life of a biomaterial - the use of special preservatives. In laboratory practice, systems with solutions are often used that record the state of the sample at the time of collection. Such preservatives (for example, based on formaldehyde or alcohol solutions) stop the processes of decay and development of microorganisms.
If you use a system with a preservative, the shelf life can increase to 2-3 days, and in some cases up to 5-7 days, depending on the type of reagent. This is especially convenient for collecting material from children or if it is necessary to collect material on weekends when laboratories are not open. However
For example, to analyze for dysbacteriosis or bacterial culture, use preservatives absolutely notas they kill living bacteria, and the growth of colonies on nutrient media will not occur. Also, preservatives can distort the results of the search for occult blood. Therefore, before purchasing a system with a fixative, be sure to check with your doctor or laboratory whether it is suitable for your purpose.
| Type of analysis | Without preservative (refrigerator) | With preservative (refrigerator) | At room temperature |
|---|---|---|---|
| Eggs of worms | up to 8 hours | up to 2-3 days | no more than 2 hours |
| Occult blood | up to 6-8 hours | up to 3 days | not recommended |
| Bacterial seeding | up to 2-3 hours | not applicable | only immediate delivery |
| Coprogram | up to 10 hours | up to 5 days | up to 4 hours |
The use of preservatives requires the correct collection technique. Usually there is already liquid in the container, and you need to place the material there with a special spoon included in the kit, up to a certain mark. Violation of the “preservative-biomaterial” proportions can lead to damage to the sample.
Storage specifics for children and infants
Collecting tests from young children is always a lottery. Infants do not go to the toilet on a schedule, and it can be even more difficult to catch the moment of bowel movement in an older child. Parents often wonder whether it is possible to collect feces in the evening if the child is guaranteed not to go to the toilet in the morning. Answer: you can, but subject to strict rules.
For breastfed infants, stools may be loose and frequent. In this case, it is important to collect the material in a sterile container as early as possible. If the test is prescribed for hidden blood or worm eggs, evening collection is acceptable provided that it is immediately placed in refrigerator. In the morning, without removing the container from the cold in advance, it must be delivered to the laboratory.
There is a common misconception that feces cannot be collected from a diaper. Modern pediatricians and laboratory technicians agree that if you collect material from the surface of the diaper (using a sterile spoon or syringe without a needle) in the first 15-20 minutes after defecation, it is quite suitable for analysis for worm eggs and coprogram. The main thing is not to scrape the material from the absorbent layer, where it can mix with the absorbent gel, but to take the upper part.
What to do if the child went into the potty with water?
If there was water or disinfectants in the potty, such material cannot be used. Water will wash away some of the bacteria and may change the osmotic pressure, and chemicals will kill the microflora. You will have to wait until next time or use special liners in the potty for collection.
For children over one year old who are already using the potty, it is recommended to use special plastic bag inserts that are attached to the rim of the potty. This allows you to collect the material clean, without impurities of urine and water. Such a sample must also be stored in the refrigerator according to the general rules.
Typical errors during collection and storage
Even knowing the rules, people often make mistakes that nullify all efforts. One of the most common is collecting material in matchboxes, paper bags or food jars. Such containers are non-sterile, porous and can react with biomaterial. Use only pharmaceutical containers.
The second mistake is freezing. Many people believe that storing it in the freezer longer is better. This is a fatal mistake. When frozen, ice crystals destroy the cell walls of bacteria and helminth eggs. After defrosting, under a microscope you will see just a mess of cellular debris, and the laboratory assistant will write “the material is not suitable for research.”
The third mistake is adding water. Some people try to wash away dense stool with water to make it easier to collect it in a container. This is strictly forbidden. Water changes the specific gravity, pH and osmotic pressure of the sample, making it impossible to conduct a qualitative analysis.
⚠️ Warning: Do not use enemas or laxative suppositories to collect stool unless specifically prescribed by a doctor for a specific type of test (for example, to look for certain parasites). Foreign chemicals will distort the chemical composition of feces.
It is also a mistake to store the material next to strong-smelling foods (fish, spices, onions). The plastic of the containers, although inert, with prolonged contact in the confined space of the refrigerator can allow volatile substances to pass through, which could theoretically affect chemical tests.
Transportation and preparation for delivery
The last stage is delivery. Even if you have stored the sample properly in the refrigerator, it still needs to be transported correctly. In the summer or during a long journey, the temperature difference can be critical. Use thermal bags or cooler bags with refrigerant (cold accumulators), especially if the journey to the laboratory takes more than 30-40 minutes.
Do not place the container directly on the ice. Sudden local supercooling can damage the structure of the sample. Wrap the container in a towel or napkin and place it near the refrigerant. This will create a buffer zone and maintain a stable temperature.
Before leaving the house, check that the lid is tightly screwed on. Shaking in transport should not lead to leakage. If you are taking an occult blood test, make sure that you did not brush your teeth with a hard brush the morning before, as microtrauma to the gums may give a false positive result.
In the laboratory, the material is immediately registered. If you brought in material that has been stored for too long, the registrar may alert you to this. In this case, it is better to listen to the advice of a specialist and retake the analysis than to get a questionable result.
Frequently asked questions (FAQ)
Is it possible to store feces for analysis in the freezer?
No, absolutely not. Freezing destroys the cellular structure of bacteria, helminth eggs and other elements, making the sample unsuitable for microscopic and bacteriological examination. After defrosting, you will receive an uninformative result.
What to do if the stool is collected in the evening, and in the morning the child did not go to the toilet?
If the analysis does not strictly require morning collection (check with your doctor), you can try to collect evening material, but you need to store it in the refrigerator for no more than 8-10 hours. To analyze dysbacteriosis, it is better to collect fresh morning material, even if you have to make an appointment at a later time in the laboratory.
Does taking antibiotics affect the storage of feces?
Taking antibiotics affects the composition of the microflora, and not the possibility of storage. However, if you are tested for dysbiosis, antibiotics should be stopped 2-3 weeks before collection (in consultation with your doctor). Such material must be stored especially carefully, since the balance of the flora is disturbed.
Is it possible to collect feces from oilcloth or fabric?
You can collect feces from oilcloth if it is clean and dry. From fabric (sheets, towels) - it is extremely undesirable, since the fabric absorbs the liquid fraction, which contains the most diagnostically important elements, and may contain powder residues. It is better to use a clean pot or vessel.
How long does it take to deliver the material to the laboratory?
Delivery time should not exceed 2 hours for bacterial cultures and 6-8 hours for other tests, if the material is not preserved. Consider travel time, registration and waiting in line. If the journey takes more than an hour, use a cooler bag.