Collecting biomaterial for laboratory research is a process that requires strict adherence to the rules, on which the accuracy of the diagnosis directly depends. Many patients mistakenly believe that the time between collection and delivery to the laboratory does not matter, but this is not the case. Biological samples are subject to changes under the influence of the external environment, and even a short-term violation of storage conditions can distort the picture.
The question most often arises as to whether a visit to the doctor or collection of material can be postponed in the evening, saving the sample until the morning. The answer depends on the type of research, but in most cases refrigerator becomes the only available method of conservation. It is important to understand that a household refrigerator is not a professional laboratory environment, and temperature fluctuations here can be significant.
In this article we will examine in detail how long it is allowed to store feces at a temperature of +2 to +6 degrees Celsius for various types of analyses. You will learn how to properly prepare the container, why you can’t freeze the material, and what mistakes most often lead to false results.
Dependence of the timing on the type of study
The first thing you need to do before collecting is to check with your doctor or laboratory about what kind of analysis to be passed. Different research methods require different degrees freshness of biomaterial. There is no universal “one hour” rule, although it is the gold standard for many types of diagnostics.
The most time-consuming is the analysis of helminth eggs protozoa. In warmth, the larvae can begin to develop or, conversely, collapse, making them invisible under a microscope. For a coprogram (general analysis), the timing is a little more flexible, but even here there are strict restrictions on preserving the morphology of fibers and cells.
There is also an analysis for occult blood, which requires a special diet and caution during storage, since bacteria in the sample can consume hemoglobin, underestimating the indicators. If you are not sure about the type of study, it is better to focus on the strictest time frame.
⚠️ Attention: To analyze for dysbacteriosis, the material must be delivered to the laboratory within 2-3 hours. Refrigerated storage for this type of research is often not recommended or is allowed only in special transport media, since anaerobic bacteria quickly die in air even at low temperatures.
Optimal temperature conditions and storage conditions
The main condition for the safety of the sample is a stable temperature. A standard refrigerator shelf, where food is usually stored, provides a range of +2 to +6 degrees Celsius. It is this mode that allows you to slow down fermentation, but does not freeze the material. bacterial processes and fermentation, but does not freeze the material.
It is strictly forbidden to place the container next to the freezer or on a shelf at the back wall, where the temperature can drop below zero. Freezing leads to the destruction of the cellular structures of red blood cells and leukocytes, and also changes the physicochemical properties of feces, making research uninformative.
The best place for temporary storage is the middle shelf of the refrigerator, away from the door, where the temperature jumps every time it is opened. The container must be tightly closed to prevent the entry of foreign odors and microorganisms from the outside.
Storage periods for various tests
The time during which the biomaterial remains suitable for research varies. Below is a table that will help you navigate the acceptable intervals. Remember that the countdown of time begins from the moment of defecation, and not from the moment it is placed in the refrigerator.
| Type of analysis | Maximum period at room temperature | Maximum period in the refrigerator (+2...+6°C) | Is it acceptable freezing |
|---|---|---|---|
| Coprogram (general) | up to 2 hours | up to 8-10 hours | No |
| Eggs of worms and protozoa | up to 1 hour | up to 5-6 hours (maximum until morning) | No |
| Occult blood | up to 3 hours | up to 6-8 hours | No |
| Analysis for carbohydrates | up to 1 hour | Not recommended | No |
As can be seen from the table, storing in the refrigerator allows you to gain several hours, which often makes it possible to hand over the collected material in the evening, the next morning. However, for analysis of carbohydrates (lactose deficiency), even short-term storage can be critical due to rapid fermentation.
If you are storing the sample overnight (from evening to morning), try to minimize the time the container is at room temperature before placing it in the cold. Immediately after collection, close the lid tightly and put it in the refrigerator.
Rules for collecting and preparing the container
The quality of the analysis depends not only on the storage time, but also on the correct collection. To do this, you need to use a sterile container, which can be purchased at any pharmacy. The use of household containers (matchboxes, food jars) is unacceptable, since foreign substances may remain on their walls.
The collection process should prevent the ingress of urine or water from the toilet. To do this, it is recommended to use a clean vessel or stretch cling film over the toilet. The material is collected using a special spoon built into the lid of the container from 3-4 different places.
☑️ Checklist for preparation for collection
The volume of material should be approximately the size of a walnut (5-10 grams). Too small an amount may not allow the laboratory technician to conduct a full examination, and an excess creates difficulties during transportation and storage.
⚠️ Attention: If you are taking antibiotics, bismuth or iron preparations, or doing enemas or using rectal suppositories, tell your doctor. These factors can distort the result, and storage in the refrigerator will no longer help here - you will need to reschedule the analysis date.
Typical errors when storing samples
One of the most common mistakes is an attempt to “improve” preservation by freezing. Place the container in the freezer strictly prohibited. Ice crystals rupture the membranes of cells and eggs of parasites, making them unidentifiable.
Another mistake is storage in unsealed containers. If the container is not closed tightly, the stool dries out, loses moisture, and the concentration of elements changes. In addition, an open container contaminates the food in the refrigerator, which violates sanitary standards.
Some patients try to preserve the material by placing it on the balcony in winter. This is a gross mistake: the temperature on the balcony is uncontrollable, the material may freeze or, conversely, be exposed to sunlight and heat during the day. Only a stable refrigerator indoors guarantees safety.
What to do if the material is frozen?
If you notice that the container is frozen, there is no point in taking such an analysis. The results will be false. It is necessary to collect a new sample, following all the rules. Do not try to unfreeze the material - the structure has already been irreversibly damaged.
The influence of time on the reliability of the results
Why is time so important? Active biochemical processes continue in the feces. Bacteria continue to multiply, consuming nutrients and releasing waste products. This changes the pH environment, the number of leukocytes and red blood cells.
During long-term storage, even in the cold, lysis (destruction) of blood cells begins. If there were red blood cells in a fresh sample, indicating bleeding, then after 10-12 hours they can completely dissolve, and the analysis will show a negative result.
The consistency and smell also change, which is important for macroscopic assessment. The laboratory technician may incorrectly assess the degree of stool formation or the presence of mucus if the sample has been sitting for too long.
Transportation of biomaterial to the laboratory
After removal from the refrigerator, the sample must be delivered to the laboratory as quickly as possible. In the warm season, it is better to use a thermal container or cooler bag with refrigerant to avoid sudden temperature changes and heating of the material during travel.
Do not leave the container in the car in direct sunlight or near heating appliances. Even short-term heating to +30...+40 degrees will trigger irreversible deterioration processes.
Be sure to have a direction and a passport with you. Your information must be clearly indicated on the container: full name, date and time of collection. Without labeling, the laboratory has the right not to accept the material.
Is it possible to collect stool in the evening if you go to the laboratory in the morning?
Yes, for most general tests (coprogram, worm eggs), collection in the evening is acceptable, provided it is stored in the refrigerator at a temperature +2...+6°C. The shelf life should not exceed 8-10 hours.
What will happen if you do not put the feces in the refrigerator?
At room temperature, the processes of rotting and fermentation occur very quickly. After 2-3 hours, the composition of the biomaterial will change so much that the analysis result will be false. Leukocytes will be destroyed and bacteria will multiply.
Is it possible to freeze stool for analysis?
No, freezing is strictly prohibited. Ice destroys the cellular structures and eggs of parasites, making them invisible under a microscope. Analysis of frozen material has no diagnostic value.
Is it necessary to heat the container before handing it over?
No, there is no need to specifically heat the material. However, a sharp temperature change (from the freezer or from the balcony) is also harmful. It is optimal if the container has a temperature close to room temperature at the time of delivery, but without forced heating.