Collecting biomaterial for laboratory research is a responsible procedure, the correct preparation of which directly determines the accuracy of the diagnosis. Many patients are faced with the question of what to do if it is not possible to deliver the container to the laboratory immediately after a bowel movement, especially if we are talking about early morning collections when clinics are still closed. In such situations, there is a need to preserve the sample in conditions as close as possible to natural ones, but slowing down the processes of destruction.
The refrigeration chamber is the most affordable and effective way to preserve biological material for a short period. However, it is important to understand that this is not a universal solution for all types of research. Temperature conditions and holding time critically affects the preservation of cell structure, helminth eggs and the composition of the bacterial flora. Violation of storage rules can lead to a false negative result, which will require repeating the procedure and wasting time.
In this article we will analyze in detail the permissible time intervals for various types of tests, the rules of packaging and placement of the container, and also indicate situations when storage is strictly prohibited. Proper organization of the collection process will help you avoid common mistakes and obtain reliable medical data.
Factors affecting the quality of biomaterial during storage
Feces are a complex mixture of undigested food debris, bacteria, intestinal epithelial cells and metabolic products. Immediately after leaving the body, fermentation and decay processes begin to actively occur in the sample, which can distort the real picture of the state of the gastrointestinal tract. That is why the time factor is decisive: the faster the material gets for research, the higher its diagnostic value.
The main enemy during storage is room temperature, which creates ideal conditions for the proliferation of opportunistic microflora. Bacteria begin to actively divide, changing the quantitative ratio of species, which makes accurate data impossible. In addition, under the influence of enzymes, leukocytes and red blood cells are destroyed if they are present in the stool due to inflammatory processes or bleeding. bacteriological culture. In addition, under the action of enzymes, white blood cells and red blood cells are destroyed if they are present in the stool due to inflammatory processes or bleeding.
Cooling allows you to slow down these biochemical reactions, but does not stop them completely. It is also important to take into account the consistency of the stool: liquid diarrheal stool loses its properties faster than formed stool. The preservation is also affected by the presence of impurities, such as mucus or pus, which require special attention during transportation.
⚠️ Attention: If you are taking antibiotics or other antibacterial drugs, the shelf life of the material for bacterial culture can be significantly reduced, since the activity of the drugs in the body continues outside it.
General rules for collection and preparation for storage
Before starting the procedure, it is necessary to prepare all accessories in advance in order to minimize the time of contact of the material with the external environment. The standard requirement is to use a clean, dry vessel or pot that has been pre-treated with boiling water. You cannot collect material directly from the toilet, as the water contains disinfectants and foreign bacteria that will make the analysis useless.
The defecation process should take place in a prepared container. After this, using a special spatula attached to the lid of the container, the material is collected. It is necessary to take samples from different places in the feces, especially if mucus, blood or undigested food are visible. This will ensure that the sample is representative for laboratory research..
The container should be filled approximately one-third, without compacting the contents. The cap should be screwed on tightly immediately after collection to prevent the sample from drying out and air from entering. The tightness of the packaging is a key condition to avoid contamination of the refrigerator shelf and the spread of an unpleasant odor.
☑️ Rules for collecting analysis
Storage periods for various types of studies
The time during which the biomaterial retains its properties directly depends on the purpose of the analysis. Different diagnostic methods require different degrees of preservation of cell structure or microorganism viability. Below is a detailed table systematizing the acceptable time frames for the main types of studies.
| Type of analysis | Maximum period at +2...+4°C | Optimal delivery time | Critical changes |
|---|---|---|---|
| Coprogram (general) | Up to 8-10 hours | 2-3 hours | Destruction of fiber, change in pH |
| Eggs of worms (helminths) | Up to 5-8 hours | Up to 4 hours | Destruction of egg membranes, lysis |
| Occult blood | Up to 6 hours | Immediately | Oxidation hemoglobin, false result |
| Bacteriosis (dysbacteriosis) | No more than 2-3 hours | Up to 1 hour | Growth of foreign flora, death of anaerobes |
For coprogramswhich evaluates the digestive capacity of the stomach and intestines, storage in the refrigerator for up to 8 hours is allowed, but laboratory assistants recommend bringing the material within 2-3 hours. During this time, morphological changes are minimal. With longer storage, the color and reaction of the medium may change, which will complicate the interpretation of the results.
Analysis of worm eggs and protozoa is more sensitive to time. Although the shells of the eggs are quite strong, long-term storage can lead to their destruction or, conversely, to the beginning of the development of larvae, which will change the picture. To detect active forms of protozoa, the material must be delivered warm and examined within 30-60 minutes; storage in the refrigerator in this case is often not recommended.
Why should you not freeze feces?
Freezing leads to the formation of ice crystals that destroy the cell walls of bacteria and eggs parasites, making the sample unsuitable for microscopy and culture.
Storage features for occult blood analysis
Detection of occult blood in the stool is an important screening test for the early diagnosis of colorectal cancer and ulcerative lesions. The technique is based on the detection of hemoglobin, which is quickly destroyed by enzymes and bacteria in the stool. Even short-term storage can cause the iron in hemoglobin to oxidize, making it invisible to reagents.
If you are collecting material for this test, try to get it to the laboratory within 2-3 hours. As a last resort, storage in the refrigerator at a temperature of +2 to +4 degrees Celsius is allowed for no more than 6 hours. However, it should be remembered that the likelihood of obtaining a false negative result increases with every minute.
There are also immunochemical tests (iFOBT), which are more stable and can remain accurate a little longer, but the classic Gregerson reaction requires maximum efficiency. Before taking the test, you must follow a diet excluding meat and iron-containing foods, so as not to distort the chemical composition of the sample.
⚠️ Attention: Do not store the material for occult blood analysis near strong-smelling foods or chemicals, as volatile substances can affect the chemical reactions during testing.
Bacteriological nuances culture and analysis for dysbacteriosis
Bacteriological research is the most demanding type of analysis in storage times conditions. Its purpose is to determine the quantitative and qualitative ratio of microorganisms in the intestine. Any change in temperature or storage time upsets the balance: some bacteria begin to actively multiply, others, especially anaerobes, die upon contact with oxygen.
The ideal option for bacterial culture is to deliver the material to the laboratory within 30-60 minutes after defecation. If this is not possible, short-term storage in the refrigerator is allowed, but no more than 2-3 hours. In this case, the container should be as airtight as possible to minimize the access of oxygen.
Some laboratories offer special transport media with preservatives that can extend the life of bacteria to 24 hours or more. If you use such a container, follow the manufacturer's instructions. An ordinary sterile glass without a preservative is not suitable for long-term storage for the purpose of bacteriology.
Temperature conditions and proper placement in the refrigerator
To preserve the biomaterial, it is critical to maintain the correct temperature conditions. The optimal range is considered to be from +2 to +4 degrees Celsius. This is the standard temperature on the middle shelf of the refrigerator. Placing the container on the door is undesirable, since the temperature there fluctuates (fluctuates) due to frequent opening, which can lead to partial freezing or, conversely, heating.
It is strictly forbidden to place the container with the analysis in the freezer. Freezing completely destroys the cellular structure, making it impossible to detect eggs helminths and kills most bacteria. Also, do not place the container directly at the back of the refrigerator, where the temperature may drop below zero.
Make sure the container is securely closed and labeled. It is best to place it in a separate, clean plastic bag to eliminate any risk of food contamination. Even a minimal leak can become a source of infection for household members.
When storage is strictly prohibited
There are situations when trying to save material for analysis does not make sense and may lead to misdiagnosis. First of all, this concerns research on enterobiasis (pinworms). For this analysis, a scraping is made from the perianal folds, and the material must be delivered immediately; storage is unacceptable.
Also, you should not store feces if it shows clear signs of decomposition, the color has changed to an unnatural one, or a sharp, different from normal smell has appeared. This suggests that the processes of decay have already begun irreversibly. In such cases, the result of the analysis will be uninformative, and the procedure will have to be repeated.
If more than the time specified for your type of analysis has passed since the collection, it is better not to risk it and collect new material. A false diagnosis based on a spoiled sample can lead to unnecessary treatment or missed serious disease.
⚠️ Attention: Always check with your laboratory for current requirements, as the reagents and procedures used there may have specific storage time limitations.
Frequently Asked Questions (FAQ)
Is it possible to store stool for analysis in the refrigerator overnight?
For most general tests (coprogram, worm eggs), overnight storage (8-10 hours) is allowed, but is not ideal. The result may be less accurate. For bacteriological culture, overnight storage is strictly not recommended.
What to do if a child went to the toilet at night and needs to be tested in the morning?
Collect the material in a sterile container immediately after defecation, close tightly and place in the refrigerator. In the morning, as soon as possible, take the sample to the laboratory. Try to ensure that the total storage period does not exceed 8 hours.
Does the fact that feces have been in the refrigerator affect the analysis?
Yes, there is an effect. When cooled, the structure of the sediment changes, and leukocytes and some types of protozoa may be destroyed. However, for routine diagnosis of helminthiasis and general assessment of the functioning of the gastrointestinal tract, short-term storage is acceptable.
Can I use a regular plastic container from home?
It is not recommended to use regular containers, since they are not sterile and may contain residues of detergents or other chemicals. It is better to purchase a special pharmaceutical container with a spoon, which guarantees the purity of the sample.
Is it necessary to heat the material before donation if it was in the refrigerator?
No, there is no need to specially heat the material. A sudden change in temperature can trigger unwanted reactions. It is enough to deliver the container to the laboratory in the form in which it was stored, the laboratory assistants themselves will bring it into the desired state for research.