How long can you store feces in the refrigerator? refrigerator: rules for accurate analysis

Storing feces in the refrigerator is not the most pleasant, but sometimes necessary procedure. Most often, this is required for tests (coprogram, worm eggs, dysbacteriosis, calprotectin), when the biomaterial is collected in the evening, and the laboratory accepts it only in the morning. However improper storage may distort the results or make them completely unusable. In this article, we will look at exactly how long you can keep feces in the refrigerator, at what temperature, in what container - and why some laboratories refuse to accept “yesterday’s” samples.

It is important to understand: feces are a biologically active mediumwhere the processes of fermentation, microbial proliferation and enzyme breakdown continue. Even within a few hours, under unsuitable conditions, the composition can change so much that the analysis will show a false negative or false positive result. For example, at room temperature after 4–6 hours leukocyte level feces decrease by 30–40%, and the concentration of some parasites (for example, Giardia) drops to an undetectable level.

We studied the recommendations of leading laboratories (Invitro, Helix, Hemotest), WHO standards and research by microbiologists to give clear answers. In the article you will find not only shelf life, but step-by-step instructions on preparation of the container, as well as a list of mistakes that 90% of patients make. If you have to get tested, save this page to your bookmarks!

Why stool cannot be stored for a long time: what happens to biomaterial

Stool is not a static object, but a dynamic biological system. From the moment of defecation, processes are launched in it that distort test results:

• 🦠 Bacterial reproduction: E. coli, enterococci and clostridia double the population every 20–30 minutes at room temperature. This leads to false dysbacteriosis.
• 🧬 Decomposition of parasite DNA: Helminth eggs (roundworms, pinworms) lose their shell after 6-8 hours, and they cannot be identified under a microscope.
• 🔬 Change in pH: The acidity of stool shifts to the alkaline side, which masks inflammatory processes (for example, occult blood).
• 💧 Moisture evaporation: The sample becomes dry, which makes it difficult to prepare smears for microscopy.

Laboratory often do not warn that Even 12 hours in the refrigerator can make the test for Giardia or rotavirus uninformative. For example, for PCR diagnostics (detection of pathogen DNA), it is critical to preserve the nucleic acid chains - and they are destroyed if stored incorrectly. As a result, the doctor may miss the infection or, conversely, prescribe unnecessary treatment.

Another problem is (contamination) of the sample. If the container is not properly closed or stored near food, foreign microorganisms (for example, yeast from kefir or mold from cheese) may get into the stool. This is especially true for tests for dysbiosis, where the exact ratio of microbes is important. contamination (contamination) of the sample. If the container is not properly closed or stored near food, foreign microorganisms (for example, yeast from kefir or mold from cheese) may get into the stool. This is especially true for tests for dysbacteriosis, where the exact ratio of microbes is important.

Official shelf life of stool in the refrigerator: laboratory data

We have collected recommendations from large diagnostic centers and compiled them into a table. Please note: times depend on the type of analysis! For example, feces for occult blood cannot be stored for longer than 6 hours, but for coprogram a day is acceptable.

Important: some laboratories (for example, Hemotest) indicate that for PCR tests (detection of DNA of viruses, bacteria) storage in the refrigerator is unacceptable — The sample must be delivered within 2 hours. This is due to the fact that DNA chains begin to fragment already at +4°C. Check the requirements of a specific laboratory!

⚠️ Attention: If you are donating stool for forensic examination (for example, for drugs or toxins), storage periods are strictly regulated - no more than 4 hours at +4°C. Otherwise, the results will not have legal force.

At what temperature should feces be stored: why +4°C is the best option

Storage temperature is a key factor. Most laboratories recommend +2…+8°C, but it is +4°Cthat is considered optimal. Why?

• 🧊 Below +2°C: Some microorganisms (for example, Campylobacter) die, which distorts the picture of dysbiosis. In addition, the moisture in the sample crystallizes and is difficult to examine.
• ❄️ 0°C and below (freezer): Helminth eggs and protozoa (giardia, amoebas) are completely destroyed. Analysis for parasites will become useless.
• 🔥 Above +8°C: The proliferation of opportunistic bacteria (Klebsiella, Proteus) accelerates, which leads to false positive results.

How to achieve stable +4°C in a home refrigerator?

1. Place the sample on middle shelf (not on the door! The temperature fluctuates there when opened).
2. Use thermometer for the refrigerator (costs ~300 rubles) to make sure that the temperature does not go beyond +2...+6°C.
3. Do not place the container next to foods that generate heat (hot dishes, dairy products).

An interesting fact: in medical refrigerators for storing biomaterials, special low-frost chambers with forced air circulation are used. This prevents condensation from forming on the containers. At home, a similar effect can be achieved if you wrap the container with a paper towel (it will absorb excess moisture).

What container to store feces in: why a pharmaceutical container is better than a mayonnaise jar

Mistake No. 1, which 70% of patients make, is using the wrong container. Glass jars, plastic food containers or bags This is why they are not suitable:

• 🧴 Residues of fat/detergents: Even after washing, molecules remain on the walls that react with fecal enzymes and distort the coprogram.
• 🚫 Leakage: Stoppers from jars allow air to pass through, which accelerates the oxidation of the sample.
• 🦠 Contamination: "Home" containers already have their own bacteria (for example, from yogurt or marinades).

The only correct option is special sterile container with a spoon from the pharmacy (costs ~50–100 rubles). It is:

• ✅ Made from polypropylene a material that does not react with biomaterial.
• ✅ Has sealed lid with a silicone gasket.
• ✅ Passes gamma sterilization - destroys all foreign microorganisms.

If you urgently need a container, and pharmacies are closed, you can use a new plastic medicine jar (for example, for vitamins), but you need it:

1. Wash with laundry soap.
2. Rinse boiling water.
3. Dry in the microwave for 2-3 minutes (this kills most bacteria).

Buy a sterile pharmaceutical container with a spoon|

If you use homemade containers, sterilize them with boiling water and microwave|

Sign the container (full name, date, time of collection)|

Place the sample in the refrigerator within 30 minutes after collection|

Isolate from food (for example, put in a zip bag)-->

⚠️ Attention: Never use cardboard boxes (for example, from matches) or foil! The cardboard absorbs moisture and the foil oxidizes, rendering the analysis unusable. Also avoid containers with dyes —they can react with stool pigments (for example, bilirubin).

How to properly collect and store feces: step-by-step instructions

For the analysis to be accurate, it is not enough to simply put the feces in the refrigerator. It is important to follow the collection algorithm:

1. Preparation:
   • 3 days before collection, exclude activated charcoal, iron preparations, laxatives foods that color feces (beets, blueberries).
   • Wash with neutral soap (no antiseptics!).
2. Collection of material:
   • Use clean dry container (pot, vessel) or special plastic funnel (sold at the pharmacy).
   • Take 3-5 pieces from different parts of the stool (top, sides, inside) - this increases the chance of detecting parasites.
   • Volume: approximately 1-2 teaspoons spoons (5-10 g).

Storage:

• Place the container in the refrigerator no later than 30 minutes after defecation.
• Temperature: +4°C (middle shelf).
• Term: see the table above (from 4 to 72 hours depending on the analysis).

Features for different tests:

• 🩸 For occult blood: Do not collect feces during menstruation or with bleeding hemorrhoids nodes.
• 🦠 For dysbacteriosis: If you are taking probiotics, stop them 2 weeks before the test.
• 🐛 Egg worms: Collect stool in morning hours — parasites are most active.

What to do if the stool is liquid (with diarrhea)?

For diarrhea, use pipette or syringe without a needleto transfer ~5 ml of material into container. Close the lid as tightly as possible and store vertically (so that the liquid does not leak). For tests for infections (salmonellosis, rotavirus), such a sample must be delivered to the laboratory within 2 hours even a refrigerator will not save from the destruction of pathogens.

If you have to take feces for carbohydrates (analysis for infants), the rules are different: the sample must be delivered to the laboratory within 4 hours, since lactose and other sugars are quickly metabolized by bacteria. In this case, storing in the refrigerator will not help - you need to take it right away.

What not to do when storing feces: top 5 mistakes

Even if you did everything “according to the instructions,” one minor mistake can spoil the analysis. This is what is strictly prohibited:

1. Store in the freezer:

   At −18°C they destroy helminth egg shells and cell membranes of bacteria. The analysis for parasites and dysbiosis will be false negative.

2. Use non-sterile containers:

   Jars from mayonnaise, baby puree or cosmetics contain residues of fats and preservatives that react with fecal enzymes. For example, benzoate sodium (preservative E211) can give a false positive reaction to occult blood.

3. Keep the container on the refrigerator door:

   The temperature there ranges from +10°C (when opening) to +2°C. For comparison: in the main chamber the amplitude does not exceed ±1°C.

4. Collect feces after an enema or laxatives:

   An enema washes out the natural microflora, and laxatives (for example, Fortrans) change the osmolarity of feces. The analysis for dysbacteriosis will be incorrect.

5. Store longer than the permissible period:

   Laboratory often do not check the “freshness” of the sample, but if the feces were stored longer than normal, the results are canceled. For example, in Invitro if such an error is detected, they issue a certificate: “The sample is unsuitable for research.”

⚠️ Attention: If you donate feces for immunochemical analysis (for example, for calprotectin), avoid contact of the sample with metal objects (spoons, tweezers). Metals catalyze the oxidation of proteins, and the test may show an overestimated result.

Another common mistake is mixing stool before analysis. This destroys the structure of the parasites and makes it impossible to assess consistency (an important parameter of the coprogram). If you need to take several portions, take them with different spoons from different places.

What to do if it is not possible to quickly deliver stool to the laboratory

Sometimes Circumstances are such that it is impossible to deliver stool within 2–6 hours (for example, the laboratory is open only on weekdays, and the sample is collected on Friday evening). In such cases:

• 📦 Use preservatives:

  Some laboratories provide special tubes with a preservative (for example, SAF fixative for parasites or buffer solution for calprotectin). In them, the sample can be stored for up to 72 hours, even at room temperature.

• ❄️ Buy a cooler bag:

  If you need to take stool to another laboratory (for example, to another city), use thermal bag with cold cells (+4°C). The sample will remain suitable for up to 12 hours.

• 🏥 Check with the laboratory:

  Some centers (for example TSIR) accept stool that has been stored for up to 24 hours, if collected in special transport container with a gel stabilizer.

If you are forced to store feces for longer than a day, inform the laboratory assistant about this. Perhaps he will make a note on the referral form, and the doctor will take this into account when interpreting the results. However, be prepared that they may refuse to accept the analysis or issue a certificate with the caveat: “The sample was stored longer than the regulated period - distortions are possible.”

As a last resort, you can freeze stool, but only for molecular genetic analysis (PCR). To do this:

1. Divide the sample into portions of 0.5 g.
2. Place in cryotubes (sold in laboratory stores).
3. Freeze at −20°C.
4. Thaw immediately before delivery to the laboratory.

This method is only suitable for detection of pathogen DNA (for example, Helicobacter pylori), but not for coprogram or analysis for worm eggs!

FAQ: Frequently asked questions about storing feces

Is it possible to store feces at room temperature?

No, if we are talking about most tests. At +20...+25°C, after 4 hours active growth begins, which distorts the picture of dysbacteriosis. An exception is samples in special preservatives (for example, Clostridium difficile And Enterococcus, which distorts the picture of dysbiosis. An exception is samples in special preservatives (for example, SAF for parasites), which allow you to store stool for up to 24 hours without refrigeration.

What happens if the stool was stored in the refrigerator for longer than the permissible period?

The consequences depend on the analysis:

• 🦠 Dysbacteriosis: False predominance of lactobacteria or Escherichia coli.
• 🩸 Occult blood: False negative result (hemoglobin is destroyed).
• 🐛 Eggs of worms: Parasites lose their membranes and cannot be identified.

The laboratory may not notice that the sample is old, but the results will be inaccurate.

Can it be used urine container for feces?

No! Containers for urine are not airtight (the lid often leaks air) and do not have a spoon for collecting. In addition, traces of salts and proteins from urine may remain on their walls, which react with fecal enzymes. The exception is universal containers labeled "for feces/urine", but they are rare.

How to store feces if you need to take a test for a child?

For infants:

• Collect feces from diaper (not from the diaper - the gel absorbs liquid and distorts the result).
• Use children's sterile containers with a small spoon.
• Store no longer 4 hours —enzymatic processes occur faster in children's feces.

For children over one year old, the rules are the same as for adults.

Is it possible to store feces in the freezer if the analysis is for PCR?

Yes, but only if:

• The sample is divided into portions of 0.3–0.5 g.
• Freezing occurs at −20°C (not in the freezer with know frostwhere the temperature fluctuates).
• One-time defrosting, immediately before analysis.

For coprogram or analysis for worm eggs freezing prohibited!