Collection of biomaterial for laboratory research is a critically important diagnostic stage, on which the accuracy of the diagnosis directly depends. Often patients are faced with a situation where it is necessary to take a test at a certain time, but it is not possible to physically deliver the container to the laboratory immediately after bowel movement. It is at this moment that a logical question arises about the permissible storage time and the correct conditions for preserving the sample. Incorrect storage of biomaterial can lead to irreversible changes in its composition, which will make the results unreliable. Enzymes contained in feces continue their activity even outside the body, gradually destroying cellular structures and changing the chemical balance. Understanding how long and at what temperature the container can be kept is key to obtaining an objective clinical picture.
Improper storage of biomaterial can lead to irreversible changes in its composition, which will make the results coprograms unreliable. Enzymes contained in feces continue their activity even outside the body, gradually destroying cellular structures and changing the chemical balance. Understanding how long and at what temperature a container can be kept is key to obtaining an objective clinical picture.
In this article we will examine in detail all the nuances associated with time intervals and temperature regimes. You will learn how to minimize the influence of external factors on a sample and what to do if deadlines are running out. Compliance with these rules will allow you to avoid repeated analysis and unnecessary waste of time.
Why storage time is critical
Biological material, having left the body, immediately begins to be exposed to various factors that change its original properties. The main role here is played by the intestines' own enzymes intestines, which continue to break down proteins, fats and carbohydrates. If proper conditions are not provided, the digestion process will continue, and the laboratory technician will see an altered picture that does not correspond to the patient’s real state of health.
In addition, bacteria begin to actively multiply in the sample, which can be either normal flora or pathogenic microorganisms. Their vital activity changes the pH environment, which affects the detection of occult blood and other important indicators. That is why the time interval between collection and research is strictly regulated by medical standards.
- 🦠 Changes in the bacterial background can lead to false positive or false negative results.
- 💧 Evaporation of moisture or, conversely, condensation can distort data on stool consistency.
- 🧪 Chemical oxidation reactions change the color of the sample, which is important for visual assessment.
Parameters such as the presence of leukocytes, erythrocytes and protozoa are especially sensitive to time. If kept at room temperature for a long time, these elements can be completely destroyed or, on the contrary, their number can visually increase due to the proliferation of microflora. Therefore, the question “how long can you store” is not a formality, but represents a strictly scientific requirement.
Optimal timing for different types of research
The time during which the biomaterial retains its diagnostic properties varies depending on the purpose of the research. For standard coprograms, including microscopic, macroscopic and chemical examination, the requirements are the most stringent. Ideally, delivery to the laboratory should be carried out within 1-2 hours after defecation.
However, modern preservatives and proper temperature treatment make it possible to somewhat expand this scope. If you use a sterile container and maintain a stable, low temperature, the sample's shelf life may be extended. But it is worth remembering that even in the cold, the degradation processes only slow down, but do not stop completely.
| Type of analysis | At room temperature | In the refrigerator (+2...+4°C) | With preservative |
|---|---|---|---|
| Coprogram (general analysis) | No more than 2 hours | Up to 8-12 hours | Up to 3 days |
| Analysis for occult blood | No more than 3 hours | Up to 6 hours | Up to 2 days |
| Search for helminth eggs | No more than 4 hours | Up to 24 hours | Up to 5 days |
| Bacteriological culture | Not allowed | Up to 2 hours (in a special environment) | Depends on the environment |
It is important to note that the data in the table are averaged and may vary depending on the requirements of a particular laboratory. Some modern centers are equipped with equipment that allows analysis even after longer storage, but this should not be relied upon without prior consultation. Always check the admission rules with the reception of the medical institution.
Temperature rules in the refrigerator
The main condition for the preservation of biomaterial is a stable temperature. The optimal range for storing feces for coprogram is considered to be from +2 to +4 degrees Celsius. These are the conditions that are usually maintained on the middle shelves of a household refrigerator, away from the walls and door.
It is strictly forbidden to freeze the sample. Ice crystals formed during freezing destroy cell membranes and change the structure of the sediment. After thawing, the material becomes unsuitable for microscopy, since the formed elements (leukocytes, erythrocytes, epithelium) will be deformed or destroyed.
⚠️ Attention: Do not place the container near food, especially meat or fish, to avoid cross-contamination. Also avoid storing on the refrigerator door, where the temperature constantly fluctuates due to opening.
Particular attention should be paid to the tightness of the container. Even at the correct temperature, the entry of air can cause oxidation of the sample surface. Sterile pharmaceutical jars are equipped with tight lids with silicone gaskets, which provide the necessary insulation. The use of improvised containers, for example, matchboxes or medicine jars, is unacceptable due to the risk of contamination and leakage.
☑️ Checking storage conditions
How to properly prepare a container for storage
The quality of research depends not only on time, but also on what the material is collected into. Today, pharmacies sell special sterile containers that are ideal for these purposes. They are made of inert plastic that does not react with the components of feces.
If you use a container from home, it must be absolutely clean, dry and have a tight-fitting lid. Preliminary washing and boiling of such containers is mandatory, but even after this the risk of introducing foreign impurities remains high. Therefore, doctors strongly advise using only certified medical supplies.
When collecting, it is important to avoid getting urine or toilet water into the sample. Urine can change the acidity of the environment, and toilet water often contains disinfectants or microorganisms that will distort the result. For collection, you can use a clean plastic bag stretched over the toilet seat, or a special container if it is provided for by the design of the toilet.
- 🧼 The container must be dry - even a drop of water will wash away the sample.
- 🚫 You cannot use containers that previously contained aggressive chemicals.
- 🏷️ Be sure to sign the container immediately after collection so as not to get confused.
The volume of material for coprogram is usually small - 5-10 grams is enough (about the size of a walnut). There is no need to fill the container to the brim, as this may lead to a leak during transportation. If the stool is liquid, its volume may be slightly larger, but the principle of tightness remains unchanged.
What to do if there is no pharmaceutical container?
If it is not possible to buy a sterile container right now, take a small glass jar (for example, from baby food or an injectable drug). Wash it thoroughly with baking soda, rinse with boiling water and dry. The lid also needs to be boiled. But remember that this is a temporary measure, and the risk of error is higher.
The influence of diet and medications on the safety of the sample
The chemical composition of feces directly depends on what the person ate and what medications he took the day before. Some foods and medications can accelerate fermentation or decay processes in the sample, even at low temperatures. For example, an abundance of meat food contributes to a more active release of gases and a change in odor.
Taking antibiotics, bismuth or iron preparations can radically change the color and reaction of the environment. If you are taking such medications, be sure to tell your doctor. In some cases, it may be necessary to discontinue the drug several days before the analysis in order to obtain correct data on the functioning of the gastrointestinal tract.
Diet also plays a role in the rate of deterioration of the material. Fatty foods may cause the fats in the sample to go rancid more quickly, which will change the readings to steatorrhea. Plant fiber, without undergoing rapid decay, can still change its structure under the influence of enzymes.
⚠️ Attention: If you are taking medications that affect gastric peristalsis or secretion, check with your doctor whether they need to be discontinued before taking a coprogram. Independent withdrawal of vital medications is prohibited.
Transportation: how to deliver the analysis without loss
Even if you have correctly stored the sample at home, the delivery stage to the laboratory can become critical. During the warm season or during a long trip on public transport, the temperature in the bag may rise above the permissible level. Therefore, it is important to use thermal containers or refrigerants.
For transportation, it is best to use a special thermal container with a cold element (cold accumulator). If this is not the case, you can wrap the jar in several layers of fabric and put it in a cooler bag along with frozen foods (not with them, so as not to freeze the feces). The main thing is to avoid direct sunlight and heat sources.
Shaking and sudden movements are also undesirable, as they can lead to mixing of layers and a change in the macroscopic picture. Try to carry the container vertically and carefully. If you are bringing the test in winter, do not leave it in the car, where it can freeze, or in a warm cabin, where it will quickly heat up.
Frequently asked questions (FAQ)
Is it possible to donate feces that have been in the refrigerator all night?
For a coprogram, overnight storage (8-10 hours) at a temperature of +2...+4°C is allowed, but this is the extreme limit. The quality of microscopy may be reduced. For testing for occult blood or bacteria, overnight storage is not recommended.
What happens if stool is frozen in the refrigerator?
Frozen stool cannot be donated. Ice crystals destroy cellular structures, white blood cells and red blood cells, making microscopic examination impossible. The sample will have to be thrown away and a new one collected.
Is it possible to store feces in the freezer if there is no space on the shelf?
Absolutely not. The freezer has a temperature below -18°C, which is guaranteed to destroy the structure of the biomaterial. It can only be stored in the main chamber of the refrigerator on the middle shelf.
Does the time of day of collection affect the shelf life?
The time of day does not affect the rate of spoilage, but it does affect logistics. Evening stool is more difficult to store, as it must “survive” the night. Morning stool is preferable, since it can be delivered to the laboratory warm within 1-2 hours.