Collecting biomaterial for laboratory diagnostics often confuses patients, especially when it comes to specific markers, such as calprotectin. This protein is a key indicator of inflammatory processes in the intestine, and its concentration helps differentiate functional disorders from organic diseases such as Crohn's disease or ulcerative colitis. The accuracy of the result directly depends on how correctly the sample was collected and stored until it was delivered to the laboratory.
Many people mistakenly believe that biomaterial can be stored for as long as conventional products in the refrigerator, but biochemical processes in feces continue even at low temperatures. Enzymes and bacteria contained in the intestine can destroy the proteins being tested or, conversely, change their concentration, which will lead to a false positive or false negative result. Therefore, the question of how long you can keep the container with the contents in the refrigerator is critical for the reliability of the diagnosis.
In this article we will analyze in detail the time restrictions, temperature conditions and technical nuances that must be taken into account when preparing for the analysis. Compliance with these rules will help avoid the need for a repeat procedure and provide the doctor with correct data for making a diagnosis.
The nature of calprotectin and the stability of the biomaterial
Calprotectin is a protein secreted by neutrophils in response to inflammation of the intestinal mucosa. Unlike some other biochemical indicators, this protein is high stability at room temperature, which makes it a convenient marker for screening. However, this stability is not absolute and has its own time frame, beyond which degradation of the protein structure begins.
The main enemy of accurate analysis is time. The longer a biomaterial is outside the body, the more active the processes of bacterial reproduction and enzymatic decay occur in it. Even if the sample has not visually changed, irreversible changes may already occur at the molecular level, affecting the concentration of the antigen.
⚠️ Attention: Long-term storage of feces at room temperature is strictly not recommended, as this can lead to a significant distortion of the results. The optimal solution is fast delivery to the laboratory or proper cooling.
There is a common misconception that freezing completely stops all processes. Although low temperatures do slow down the metabolism of bacteria, improper freezing or repeated thawing can lead to the destruction of cellular structures and the release of additional proteins, which will distort the picture of inflammation.
Optimal storage times in the refrigerator
The main question that concerns patients: how many hours or days can the collected material be stored in the refrigerator? According to modern laboratory standards and instructions from test system manufacturers, the shelf life of stool for calprotectin analysis in the refrigerator is from 2 to 7 days, depending on the preservative used.
If you use a standard sterile container without adding special solutions, the maximum shelf life usually does not exceed 48 hours (2 days). In this case, the temperature regime must be strictly observed in the range from +2 to +8 degrees Celsius. Exceeding this period significantly reduces the reliability of the study.
If special containers with transport buffer solutions (preservatives) are used, the shelf life of the sample can be increased to 5-7 days. The preservative stabilizes the pH of the environment and prevents the growth of bacteria, keeping the structure of calprotectin unchanged throughout the week.
It is important to consider that the refrigerator must be in working order. Sudden temperature changes, for example, when the door is frequently opened or the refrigerator compartment is defrosted, can negatively affect the safety of the biomaterial. It is recommended to place the container on the middle shelf, away from the freezer and door, where the temperature is most stable.
Temperature conditions and placement conditions
Maintaining the correct temperature is not just a recommendation, but a prerequisite for obtaining a valid result. Calprotectin is sensitive to extreme temperatures and improper storage may result in protein denaturation. The ideal range is +4°C ± 2°C.
The placement of the container in the refrigerator also matters. Do not place the container with the biomaterial directly on the back wall of the refrigerator, where the temperature may drop below zero, which will lead to partial freezing of the sample. Also, you should not keep the container on the door due to constant temperature fluctuations when opening.
To ensure tightness and protection from foreign odors (which is important for hygiene, although odors do not affect the analysis itself), it is recommended to place the container in an additional plastic bag. This will prevent accidental contamination of food in the refrigerator if the container lid is not tightly closed.
If your refrigerator is not able to maintain a stable temperature above zero (for example, the thermostat is faulty), it is better to use the services of paid laboratories offering courier travel, or find an alternative place with suitable conditions, since storage at temperatures above +10°C is already considered a violation of the protocol.
Rules for collecting and preparing the container
The quality of the calprotectin analysis depends not only on storage, but also on the correctness of collection. The test requires a small portion of feces, approximately the size of a walnut or 1-2 teaspoons. It is necessary to collect material from different parts of the feces, if they are heterogeneous, in order to obtain a representative sample.
The container must be sterile and dry. The use of matchboxes, medicine jars or food containers is unacceptable, since the remaining substances on their walls can enter into a chemical reaction with the test system reagents. Pharmacies sell special cups with a spatula built into the lid, which greatly facilitates the process.
It is important to avoid getting urine, toilet water or menstrual blood into the sample. These impurities may contain their own proteins or bacteria, which will alter the concentration of calprotectin. For collection, it is recommended to use a clean, dry vessel or stretch cling film over the rim of the toilet before defecation.
☑️ Checklist for preparing for analysis collection
After collection, it is necessary to close the lid tightly to prevent the sample from drying out and the access of oxygen, which can oxidize some components. The last name, first name and date of collection should immediately be written on the container so as not to confuse the samples if there are several tests.
Transportation of biomaterial to the laboratory
Delivery of the sample to the laboratory is the final and critical stage. If you store feces in the refrigerator at home, you need to transport it in a thermal bag or cold pack, especially if the journey takes more than 30-40 minutes or the weather is hot. Sharp heating of the sample after cooling is unacceptable.
During transportation, the container must be in a vertical position so that the lid does not leak. It is recommended to wrap the cup in several layers of paper towels and place it in a tight bag. This will protect the sample from mechanical damage and maintain hygiene.
If you cannot deliver the material on the day of collection, make sure that the laboratory accepts samples stored in the refrigerator and check with them. Some laboratories require delivery strictly on the day of collection, regardless of the use of preservatives.
| Container type | Storage conditions | Maximum period | Risk of error |
|---|---|---|---|
| Sterile (no preservative) | Refrigerator (+2...+8°C) | 2 days (48 hours) | Medium |
| With preservative | Refrigerator (+2...+8°C) | 5-7 days | Low |
| Sterile (no preservative) | Room temperature | No more than 2-4 hours | High |
| Frozen sample | Freezer (-18°C) | Not recommended* | Critical |
*Note: Freezing Most laboratories do not recommend stool for calprotectin analysis, since thawing causes destruction of cellular structures and a change in protein concentration.
Factors that distort the results of the analysis
Even with ideal storage, there are factors that can affect the level of calprotectin. One of the main enemies of accurate results is taking non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, diclofenac or aspirin. These medications can cause microdamage to the intestinal mucosa, increasing protein levels artificially.
Diet and the presence of bleeding also affect the result. Eating a lot of red meat or having hemorrhoidal bleeding may give a false positive reaction. Doctors often recommend eliminating these factors a few days before the test.
⚠️ Attention: If you are taking bismuth, iron or barium preparations, be sure to tell your doctor and laboratory technician. These substances can color the stool and interfere with the chemical reactions of the test system.
The age of the patient is also an important factor. In children under 3-4 years of age, the level of calprotectin is physiologically higher than in adults, due to the peculiarities of the formation of microflora and the immune system. Therefore, standards for children and adults differ, and samples from children must be stored with the same care.
The influence of menstruation on the analysis
During menstruation, blood can enter the stool, which significantly increases the level of calprotectin. It is recommended to postpone the test until after the end of menstruation or use a tampon to prevent discharge.
Frequently asked questions (FAQ)
Is it possible to freeze stool for calprotectin analysis?
Freezing is not recommended by most laboratories. When frozen, ice crystals destroy cell membranes, which leads to the release of intracellular calprotectin and distortion of the actual level of inflammation in the intestinal lumen. It is better to store the sample in the refrigerator at +4°C.
What should I do if I did not have time to collect the stool in 2 days?
If more than 48 hours have passed (for a regular container), the reliability of the result drops sharply. Most likely, the laboratory assistant will refuse to accept the material or the result will be marked as unreliable. In this case, the analysis must be retaken, collecting a fresh portion.
Does shaking during transportation affect the result?
Intense shaking and shaking do not affect the concentration of the calprotectin protein itself, since it is a stable molecule. However, shaking can lead to a violation of the seal of the container and contamination of the sample by the external environment, which is unacceptable.
Do you need to follow a diet before collecting stool?
A special strict diet is not required, but 2-3 days before the analysis it is advisable to exclude foods that cause intestinal irritation (acute foods, alcohol) and stop taking NSAIDs, if your health condition allows it (after consultation with your doctor).
Is it possible to collect stool in the evening if the test is in the morning?
Yes, this is acceptable. Evening collection followed by overnight refrigeration is standard practice. The main thing is to meet the total storage period (up to 2 days) and ensure the correct temperature conditions.
Remember that the calprotectin test is a powerful diagnostic tool that helps avoid more invasive procedures such as colonoscopy, in the early stages of the examination. Proper preparation and storage of biomaterial is in your hands and directly affects the quality of medical care.