Taking laboratory tests is a standard procedure that every person encounters when visiting a doctor or undergoing a routine medical examination. Situations often arise when it is not possible to deliver biological material to the laboratory immediately after defecation.
In this case, a household refrigerator comes to the rescue, allowing it to slow down the processes of fermentation and bacterial growth. However, it is critically important to understand that the refrigerator does not preserve the sample is forever, and only briefly stops biological changes.
Violation of the storage time frame or temperature regime can lead to false results, which, in turn, will lead to erroneous diagnosis and incorrect treatment. In this article, we will analyze in detail the permissible time intervals for various types of studies and the rules that will help preserve the quality of the sample.
Factors influencing the safety of biomaterial
The rate of sample degradation depends on many variables, and temperature here is only one of the parameters. The main enemy is time: the longer feces are outside the body, the more active the processes of destruction of cellular structures are in them. Enzymescontained in digestive juices continue their work even after leaving the body, gradually dissolving leukocytes and epithelium.
Temperature conditions inside The refrigerator compartment must be stable. The ideal range is from +2 to +8 degrees Celsius. If you store the container on the door, where the temperature fluctuates frequently when opened, or in a fast-freezing zone where the sample may crystallize, the result will be distorted. Freezing Most types of feces are strictly prohibited, since ice crystals destroy cell membranes.
Also plays an important role tightness of the container. The ingress of foreign moisture, microparticles or air can trigger oxidative processes. This is why the use of clean, dry, tightly sealed containers is a must for any laboratory testing.
⚠️ Attention: If you are storing occult blood test material, avoid contact with metal surfaces or caps not intended for medical samples, as this may cause a chemical reaction and a false positive result.
General analysis of stool (coprogram)
Coprogram is one of the most common studies that allows you to evaluate the functioning of the digestive tract. For this type of analysis, storage periods are the most stringent, since the microbiological composition and physicochemical properties change rapidly.
Ideally, the sample should be delivered to the laboratory within 2 hours after collection. If this is not possible, storage in the refrigerator is allowed, but no more than 6–8 hours. After this time leukocytes begin to collapse, and the number of bacteria changes its ratio, which makes microscopy uninformative.
Particular attention should be paid to consistency and color. If stored for a long time, even in the cold, feces may darken due to oxidation, and the odor may become more pungent. These changes can be interpreted by the laboratory assistant as signs of pathology, although in fact this is the result of a violation of transportation conditions.
To obtain a reliable picture, a balance must be struck between the time of collection and the time of delivery. If you are not sure that you will have time to deliver the material within 8 hours, it is better to reschedule the test for another day or use the services of laboratories that work at night or have their own collection points.
Analysis for eggworms and enterobiasis
Investigation for the presence of helminth eggs and their larvae is more resistant to external influences than coprogram. The eggs of most parasites have a dense shell that protects their contents from drying out and temperature changes.
The shelf life of such material in the refrigerator can be up to 24 hours, and in some cases up to 48 hours if special preservative solutions are used. However, delivery within the first 4-6 hours is still considered the gold standard. Long-term storage can lead to the fact that the larvae begin to emerge from the eggs, which will complicate their identification under a microscope.
When collecting material for enterobiasis (scraping), the situation is different. The adhesive tape or cotton swab from the surface of the anus should be delivered to the laboratory as quickly as possible, preferably within 2 hours. It is not recommended to store scrapings in the refrigerator, as condensation can dissolve the adhesive base or damage the sample.
Therefore, doctors often recommend taking the test three times at intervals of several days, observing the storage rules each time.
Test for occult blood
Identification of occult blood in the stool is an essential stage of diagnosis diseases of the gastrointestinal tract, including ulcers and cancer. The sensitivity of modern tests is extremely high, which imposes strict restrictions on storage conditions.
For immunochemical methods (iFOBT), the shelf life in the refrigerator is up to 3 days, but only if special containers with a preservative are used. If you are collecting material in a regular dry container, it must be delivered within 6 hours. Hemoglobin contained in red blood cells is oxidized by intestinal bacteria during long-term storage, and the reaction can become false negative.
There is also a technique that requires preliminary preparation and a diet that excludes meat and iron-containing products. Violation of storage rules can nullify all dietary restrictions, since bacterial activity in the sample will change the chemical composition of the sample.
⚠️ Attention: Women should not take an occult blood test during menstruation and for 3 days after its end, since the ingress of even a microscopic amount of blood will distort the result beyond recognition.
When collecting a sample, try to take material from different parts of the feces, especially if there are visible changes (mucus, lumps). This will increase the information content of the study and reduce the risk of errors associated with uneven distribution of blood in the stool.
Bacteriological culture (dysbacteriosis)
Analysis for dysbacteriosis and intestinal infections is the most demanding in terms of transportation conditions. The purpose of the study is to grow cultures of bacteria that live in the intestines on nutrient media. Any change in the ratio of microorganisms outside the body will lead to a false picture.
Under normal conditions (room temperature), material for inoculation should be delivered within 2 hours. In the refrigerator, the period increases slightly - up to 3-4 hours, since cold inhibits the growth of not only pathogenic, but also beneficial flora (bifidobacteria and lactobacilli).
There are special transport media (for example, Cary-Blair medium) that allow you to maintain the viability of bacteria for up to 2 days or more. If the laboratory provides you with a container of such a preservative, follow the instructions on the package. Storage in a dry, sterile container is not advisable.
☑️ Rules for collecting for bacterial sowing
Errors at this stage are the most critical. If beneficial bacteria die while you are taking the test to the refrigerator, and opportunistic bacteria multiply, the doctor may prescribe unnecessary antibiotics, believing that the patient has dysbacteriosis.
Table of shelf life of various tests
For ease of perception of information, we have systematized the data on the permissible storage time in a summary table. Remember that the indicated periods are valid when stored at a temperature of +4..+8°C.
| Type of analysis | Without a refrigerator (max) | In a refrigerator (max) | Special conditions |
|---|---|---|---|
| Coprogram (general) | 2 hours | 6–8 hours | Dry, clean container |
| Eggworm | 4 hours | 24 hours | Avoid freezing |
| Occult blood | 3 hours | 6 hours (dry) / 72 hours (preservative) | Strict diet before donation |
| Bacteriosis (dysbacteriosis) | 2 hours | 3–4 hours | Preservative is desirable |
| Scraping for enterobiasis | 2 hours | Not recommended | Only in the morning, before washing |
This table serves as a guide, but you should always take into account the recommendations of the specific laboratory where you plan to take the material. Equipment and reagents may differ, which makes adjustments to the requirements for samples.
Typical errors during storage
Even knowing the theoretical terms, patients often make practical mistakes that reduce the value of the study to zero. One of the most common is storing the container in the vegetable compartment or on the refrigerator door, where the temperature is unstable.
Another mistake is using unsterile containers. Residues from household chemicals, detergents, or even just water can kill bacteria or react with reagents. It is also unacceptable to freeze stool “just in case.”
Some try to preserve the sample by adding water or other liquids to it. This is strictly prohibited, since the specific gravity and chemical composition of the sample changes. The material must be collected in a clean, dry form.
⚠️ Attention: If you accidentally froze a sample or it was left in a warm place for more than 10 hours, do not try to submit it to the laboratory. The results will be false and the money will be wasted. It’s better to retake the analysis again.
It is also worth mentioning the labeling. The container must be signed immediately after collection. In a hurry in the morning, it is easy to mix up the jars if several people in the family are tested at the same time, which will lead to the issuance of an incorrect result for a particular patient.
Rules for collection and transportation
The quality of the analysis begins with the correct collection. To do this, you need to prepare all the accessories in advance: a clean vessel (a potty, a plastic bag stretched over a toilet seat) and a sterile container with a spoon.
Feces are collected from three different areas of one portion in order to capture possible inclusions (mucus, blood, pus). The sample volume should be approximately the size of a walnut (about 5–10 grams). There is no need to take more, this will not improve the quality of the analysis.
What to do if the child does not go to the toilet in the morning?
If the test needs to be taken in the morning, and the child is used to going to the toilet in the evening, collect the material at night. For analysis of eggworms and coprograms (if rapid delivery is not possible), storage in the refrigerator until the morning is allowed. This option is not suitable for bacterial sowing - you will have to wait until the child goes to the toilet in the morning, or wake him up in advance.
When transporting in the cold season, it is better to place the container in a thermal bag or simply wrap it in a towel to avoid sudden hypothermia, which is also harmful for some types of bacteria. In the hot season, on the contrary, use refrigerants, but make sure that the container does not come into direct contact with ice.
Is it possible to store stool for analysis in the freezer?
Absolutely not. Freezing leads to the destruction of cellular structures, lysis of red blood cells and the death of most bacteria. After defrosting, the sample will become unsuitable for microscopy and bacteriological culture. The only exception is some specific virological tests, but the doctor warns about them separately and issues special test tubes.
What to do if mucus or blood appears in the stool?
Be sure to take this particular area with pathological impurities for analysis. Mucus and blood often contain the highest concentrations of pathogenic microorganisms or epithelial cells, which are critical for diagnosis. Do not mix them with the bulk, take them carefully.
Does taking medications affect the result of the analysis?
Yes, many drugs can distort the picture. Antibiotics, bismuth and iron preparations, laxatives and sorbents (activated carbon) affect the color, consistency and microbiota of stool. You must inform your doctor about taking any medications and, if possible, take a pause in taking them before taking the test, if this is approved by the attending physician.
How long is the test result valid?
The validity period of the results form itself usually ranges from 10 days to 1 month, depending on the requirements of the institution (clinic, sanatorium, pool) where you submit the document. However, biological material (stool itself) is good only for the time specified in the article (from 2 to 24 hours).
Do you need to wash yourself before collecting stool?
Yes, hygiene procedures are required. It is necessary to wash with warm water and soap to wash away microorganisms and impurities from the surface of the skin and genitals. It is unacceptable for urine or tap water to get into the sample, so use a clean vessel or pot, not a toilet.