Collecting biomaterial for laboratory research often confuses patients, especially when it comes to taking tests early in the morning or, if necessary, delivering a sample to a clinic located far from home. A matter of time becomes critical, since the accuracy of diagnosis directly depends on compliance with transportation rules. Many people mistakenly believe that biological fluids and waste quickly lose their properties, but modern preservatives and temperature conditions make it possible to extend this period.
The key factor determining how long the material is suitable for research is temperature conditions storage. A refrigerator is not just a household appliance, but a necessary equipment for preserving the structure of cells, bacteria and chemical compounds in a sample. However, it is important to understand that an ordinary shelf in the refrigerator and a specialized container with a preservative are different conditions that dictate their own rules. The maximum shelf life of feces in the refrigerator at a temperature of +2 to +8 degrees Celsius usually does not exceed 8–12 hours, but for some types of analyzes this period is reduced to 2–4 hours.
In this article we will examine in detail the nuances of storing biomaterial for various types of studies so that you can be sure of the reliability of the result. You will learn why you should not freeze a sample, how to properly prepare the container, and what to do if the collection time falls in the evening. Compliance with these simple but important rules will avoid repeated tests and loss of time.
Factors affecting the safety of biomaterial
The safety of biological material depends on many variables, among which ambient temperature plays a primary role, but is not the only one. The chemical composition of the intestinal contents begins to change immediately after defecation due to the activity of enzymes and bacteria present in the sample itself. If you do not create obstacles to these processes, the result of the study may be distorted: the number of leukocytes will change, and helminth eggs may be destroyed.
The second important factor is the type of container. The use of sterile pharmaceutical jars with a tight-fitting lid prevents the entry of foreign microorganisms and drying out of the sample. Plastic containers from food products, even thoroughly washed, are strictly not recommended, since residual detergents or fats may react with reagents in the laboratory. The tightness of the packaging also protects against the spread of odor and bacterial contamination inside the refrigerator compartment.
⚠️ Attention: Do not store the container with biomaterial on the refrigerator door. Constantly opening the door leads to temperature changes, which can negatively affect the quality of the sample. Place the container on the middle shelf, where the temperature is most stable.
The third aspect is the type of study being planned. For some tests, freshness is critical; for others, storage for 24 hours is allowed. For example, when searching for occult blood, storage time is less important than when detecting mobile protozoa, which die 15–30 minutes after leaving the body. Therefore, before collecting, always check with your doctor or laboratory about the specific requirements for your case.
Storage periods for different types of tests
The time during which stool remains suitable for analysis directly depends on the purpose of the study. Laboratories use different diagnostic methods, and each of them has its own requirements for the state of the biomaterial. Let's consider the main types of analyzes and acceptable time intervals.
For coprogram (general stool analysis), it is allowed to store the material in the refrigerator for up to 8–10 hours. In this case, it is important that the sample is protected from drying out and direct sunlight. If the analysis is taken later, the microscopic picture may change: the pH will change, some types of bacteria will disappear, which will lead to an incorrect diagnosis.
When examining the worm eggs and simplest terms, the deadlines are even stricter. The ideal option is to deliver the material within 2–4 hours. Some types of protozoa, such as amoebas, turn into cysts or die when cold, making them invisible to the laboratory technician. If you cannot deliver the sample quickly, use special preservatives that are provided in the laboratory.
- 🔬 Test for occult blood: allows storage for up to 12 hours, but requires following a diet 3 days before collection.
- 🦠 Bacteriological culture: material must be delivered within 2 hours, since extraneous microflora can begin to multiply.
- 🧪 Analysis for carbohydrates: is carried out mainly in children, the material is good for no more than 4-6 hours.
Rules for stool collection in adults and children
The process of collecting biomaterial requires compliance with a certain sequence of actions to prevent contamination of the sample. For adults, the best option is to use a clean, dry container (vessel) or plastic film stretched over the toilet. Contact with water from the toilet is unacceptable, as it may contain disinfectants or other bacteria that distort the result.
For children, the procedure may be more complicated. If the child is already using the potty, he must first be thoroughly washed with soap, rinsed with boiling water and dried. It is not recommended to collect feces from the surface of a diaper or diaper, since the absorbent layer will draw out the liquid fraction, leaving only dense lumps, which will make the analysis incomplete. For infants, you can use special urinals or sterile gas outlet tubes (for constipation, as prescribed by a doctor).
| Type of analysis | Maximum storage time | Temperature range | Preservative |
|---|---|---|---|
| Coprogram | 8–10 hours | +4...+8°C | Not required |
| Eggs of worms | 4–6 hours | +4...+8°C | Desirable |
| Hidden blood | 10–12 hours | +2...+8°C | Not required |
| Bacterial culture | 2 hours | Room or +4°C* | Special required. environment |
*Note: for bacteriological culture, conditions may vary depending on the suspected pathogen, so consultation with a doctor is required. In some cases, the material cannot be stored at all and must be inoculated immediately.
Temperature conditions and conditions in the refrigerator
Proper organization of space in the refrigerator is the key to the safety of the tests. As already mentioned, the door is the worst place to store biomaterials due to temperature instability. The optimal zone is the middle shelf or compartment for vegetables, where the temperature remains stable in the +2...+8 degrees Celsiusrange. It is this mode that slows down enzymatic processes, but does not destroy cellular structures.
It is important to ensure that the container is isolated from food. Even though the lid is sealed, additional packaging in a clean plastic bag is a smart precaution. This will prevent accidental contamination of food and protect the sample from condensation that may form on the walls of the refrigerator. Also make sure that the container does not come into contact with the back wall of the refrigerator, where the temperature may be below zero, which will lead to freezing.
⚠️ Attention: It is strictly forbidden to freeze feces for analysis! Freezing destroys cell membranes, changes the structure of parasite eggs and makes most research impossible. If you accidentally froze the sample, you will have to retake it.
If you live in a hot climate or transportation takes a long time, use thermal containers (thermal bags) with refrigerants. However, remember that direct contact of the container with the ice element is also undesirable - wrap the coolant in a towel. This will allow you to maintain coolness without the risk of local hypothermia of the biomaterial.
Use of preservatives to extend the life
In situations where delivery of freshly collected material to the laboratory within 2 hours is impossible, experts recommend the use of special preservatives. These are chemicals that fix biological material, stopping the processes of decay and proliferation of bacteria. The most common preservative is formalin or glycerin-salt mixture, but their use depends on the type of analysis.
Pharmacy kits for collecting stool often already contain a preservative liquid at the bottom of the jar. Such systems have a special spatula built into them, which allows you to take a portion of the material and immediately immerse it in the solution. The ratio is usually 1 part feces to 3 parts preservative. This allows you to increase the shelf life of the sample to 24 hours or more, as well as preserve the structure of protozoa and helminth larvae.
- 🧪 Advantages: possibility of collecting material in the evening for morning delivery, preserving the morphology of parasites.
- ⚠️ Limitations: not suitable for all types of analyzes (for example, for some biochemical tests or bakposeva).
- 💊 Availability: sold in pharmacies without a prescription, are inexpensive.
Before purchasing a canned system, be sure to check with the laboratory whether they accept the material in this form. Some modern automated analyzers require native (liquid or pasty) material without chemical additives.
Frequent errors during storage and transportation
Even knowing the rules, patients often make mistakes that nullify all efforts. One of the most common is to collect the material “in reserve” the night before without using a preservative and store it at room temperature. By morning, such a sample becomes unusable: active fermentation begins in it, the acidity and microbiological composition changes.
Another mistake is the use of dirty containers. Even microscopic residue from detergent can react with the occult blood test reagents, causing a false positive result. The third error is container overflow. The material should not fit tightly to the lid; it is necessary to leave an air gap to avoid squeezing out the contents when opening.
Specificity of tests for hidden blood and dysbacteriosis
Tests for hidden blood and dysbacteriosis require special attention. For the occult blood test (Gregerson reaction or immunochemical test), not only time is important, but also diet. However, from a storage point of view, this material is quite stable. The main thing is to avoid urine or menstrual blood getting into the sample, which can completely distort the result.
Analysis for dysbacteriosis is one of the most capricious. It is aimed at assessing the living microbial community of the intestine. Bifidobacteria and lactobacilli are very sensitive to oxygen and temperature changes. If such an analysis is not delivered to the laboratory within 2 hours (maximum 3-4 in the refrigerator), the result will show a predominance of opportunistic flora that survived, while the beneficial flora died. This can lead to an erroneous diagnosis of dysbiosis.
Is it possible to donate stool collected last night?
You can donate stool collected last night only if it was immediately placed in a preservative or refrigerator, and no more than 8-10 hours (for coprogram). For tests for dysbacteriosis and protozoa, yesterday's material, as a rule, is not suitable.
What to do if stool is liquid?
Liquid stool (diarrhea) is more difficult to collect, but necessary. Use wide-mouth containers or special funnels. Liquid material often contains more diagnostically significant elements (leukocytes, protozoa), so its delivery to the laboratory should be as fast as possible - preferably within 30-60 minutes.
Does the analysis need to be warmed before delivery?
The analysis cannot be specially warmed (on a battery, in a microwave). However, if it was stored in the refrigerator, before sending it to the laboratory, you can hold it in your hands or in a room for 15-20 minutes so that the temperature becomes equal to room temperature. This will make the laboratory assistant’s work easier when taking a sample.
Does taking medications affect the shelf life?
Taking antibiotics, bismuth or iron preparations can change the color and consistency of stool, and also affect the result of a chemical analysis. This does not affect the shelf life, but you must inform your doctor and laboratory technician about taking medications.
Following all of the above recommendations will allow you to get the most accurate test result. Remember that laboratory diagnosis is the first step towards proper treatment, and the quality of this step depends on the correct preparation and storage of the biomaterial. Take care of your health and pay attention to detail even in such delicate matters.