Collection of biomaterial for laboratory research often occurs in the morning, when it is physically impossible to get to a clinic or diagnostic center immediately. In such situations, patients are faced with the question of proper preservation of the sample until it is delivered to specialists. Errors at this stage can lead to distorted results, which will lead to incorrect diagnosis and ineffective treatment.
The refrigerator is the most accessible and common way to slow down the processes of bacterial growth and the breakdown of organic substances in the collected liquid. However, the temperature regime must be strictly defined, since too low temperatures can lead to precipitation, which laboratory technicians may mistakenly mistake for pathology. Understanding the physiological processes occurring in biomaterial outside the body will help you properly prepare for analysis.
In this article we will analyze in detail the permissible time intervals, storage features of various types of analyzes and critical mistakes that patients often make. Compliance with these rules ensures that the result you receive will reflect the real state of health, and not artifacts of improper handling of the sample.
The influence of temperature on the biochemical composition of urine
Urine is a complex biological fluid containing metabolic products, salts, epithelial cells and microorganisms. At room temperature, the processes of fermentation and proliferation of bacteria rapidly begin in it, which change acidity (pH) and the chemical composition of the sample. That is why lowering the temperature is a key factor in preservation.
The optimal range for storage is considered to be a temperature of +2 to +4 degrees Celsius. This is the standard mode of the main chamber of a household refrigerator. Under such conditions, enzymatic activity decreases, and cellular elements retain their integrity longer. If you place the container in the freezer, the water will freeze, ice crystals will destroy the cell walls, and the analysis will become uninformative.
It is important to consider that even in cold conditions, oxidation processes do not stop completely, but only slow down. Keeping the sample in the cold for a long time can lead to a change in color and the appearance of a specific odor. Therefore time interval between collection and delivery to the laboratory remains a critical parameter that cannot be ignored even under ideal temperature conditions.
Acceptable storage periods for different types of tests
The time during which urine retains its properties directly depends on the type of study prescribed. Different analyzes are sensitive to different changes: in some cases, living cells are important, and in others, the chemical composition of salts is important. For a general urinalysis (UCA), the standard period is up to 2 hours at room temperature, but in the refrigerator this period can be extended.
When stored in the refrigerator, a general urinalysis remains usable for research for 4-6 hours, up to a maximum of 8 hours if the container was sterile. However, for analysis according to Nechiporenko or Zimnitsky, the requirements may be more stringent due to the need for accurate counting of cellular elements. Bacteriological culture (bacteriological culture) requires delivery to the laboratory within 1–2 hours, since any foreign bacteria from the air can distort the picture.
Below is a table showing the dependence of the shelf life of the sample on the type of test and storage conditions:
| Type of analysis | At room temperature (+20...+24°C) | In the refrigerator (+2...+4°C) | Critical changes |
|---|---|---|---|
| General analysis (GAM) | Up to 2 hours | Up to 6–8 hours | Destruction of cylinders, growth of bacteria |
| According to Nechiporenko | 1–2 hours | Up to 4 hours | Dissolution of leukocytes and erythrocytes |
| Biochemical (daily) | Not stored | The entire collection period + 2 hours after | Change in the concentration of glucose and protein |
| Bacterial culture | Not recommended | Up to 2 hours (strictly) | Contamination with foreign flora |
It is worth noting that these terms are relevant provided that the correct container is used. If you use household jars that have not been properly sterilized, the shelf life of the sample is reduced to almost zero, since the container’s own microflora will begin to multiply instantly.
Rules for selecting and preparing a container
The first rule for successful testing is the use of a sterile container. Pharmacies sell special plastic cups with a tight-fitting lid that have already undergone the necessary processing. The use of food containers (mayonnaise, baby food) is strictly not recommended, since even after thorough washing, microparticles of fat and detergents remain on the walls.
If using a pharmaceutical container is not possible, the glass jar must be thoroughly washed with soda, rinsed with boiling water and sterilized over steam or in the oven. The lid must also be clean and tightly closed to prevent the entry of air and foreign impurities. Sealing packaging prevents leakage and odor transfer inside the refrigerator.
Before filling the container, make sure it is dry. Water ingress can change the specific gravity of urine, causing false test results. Place a label on the container with the patient's data and collection time so that there is no confusion in the laboratory, especially if several family members are taking tests.
☑️ Preparing a container for urine
Collection technique and primary processing
The urine collection process also affects for the possibility of its further storage. For general analysis, morning urine is collected. This means that you need to skip the first seconds of urination, then draw 50-100 ml into the container, and release the rest into the toilet again. This measure allows you to wash away the bacteria located in the urethra and get a cleaner sample. medium portion morning urine. This means that you need to skip the first seconds of urination, then draw 50-100 ml into the container, and release the rest into the toilet again. This measure allows you to wash away the bacteria present in the urethra and obtain a cleaner sample.
Before collection, be sure to rinse the external genitalia with warm water without using antibacterial soap, which can kill beneficial flora or, conversely, get into the sample. Women are advised to use a hygienic tampon so that vaginal discharge does not mix with urine, which is especially important for the accuracy of the analysis.
⚠️ Attention: Do not collect urine in the evening for morning delivery, unless your doctor prescribes otherwise. At night, active concentration processes occur in the body, and “yesterday’s” urine, even in the refrigerator, will have a changed composition of salts and cells.
After collection, screw the lid tightly. Do not touch the inside of the container or lid with your fingers. If you plan to store the sample, immediately place it in the refrigerator, without leaving it on the table at room temperature even for 15–20 minutes.
Features of storing baby urine
Collecting urine from babies often turns into a quest for parents. Using urine bags is the most hygienic and effective way. They are glued to the child’s skin and allow you to collect material without contact with the diaper, which instantly absorbs the liquid and changes its composition.
If you have collected urine from a child, but cannot immediately go to the laboratory (for example, the child has fallen asleep or you are waiting for the clinic to open), the storage rules are the same: refrigerator and a maximum of 2-4 hours. However, for children, the requirements for sterility are even higher, since their immune system and microflora are more sensitive, and the risk of bacteria entering the skin is higher.
Do not try to squeeze urine out of a diaper, diaper or cotton wool. In this case, lint, dyes and chemicals from the absorbent will get into the sample, and the analysis itself will be hopelessly spoiled. The laboratory will simply refuse to accept such material or will give a false positive result for protein and leukocytes.
What to do if the child does not pee in the container?
Try to turn on the sound of running water, give the child a drink of water, or put a warm diaper on the lower abdomen. Reflex urination often helps solve the problem.
Typical errors and signs of a spoiled sample
Even if the temperature regime is observed, mistakes can be made that will make the analysis useless. One of the most common is storage on the refrigerator door. There, the temperature constantly fluctuates due to the opening of the door, which leads to partial freezing and thawing of the sample. Store the container only on the deep shelves of the main chamber.
How do you know that urine can no longer be donated? If, after storing in the refrigerator, you notice that the color has turned dark yellow or brown, a strong ammonia smell has appeared, or flakes have appeared that do not disappear when shaken, it is better not to take such a sample to the laboratory. The results will be unreliable.
⚠️ Attention: If the urine becomes cloudy after cooling, this is not always a sign of spoilage. When cooled, salts (urates) may precipitate in it, which makes it cloudy. When warmed to room temperature, the turbidity may disappear. However, for the accuracy of the analysis, it is better to submit fresh material.
Another mistake is adding preservatives yourself. Some special containers for 24-hour urine have chemicals already added to them, but nothing should be added to a regular container. This will completely distort the biochemistry.
Transportation and delivery to the laboratory
When transporting a refrigerated sample, it is important to prevent its sudden heating or shaking. In winter, it is better to keep the container in your inner clothing pocket so that it does not get too cold, and in summer, use a thermal bag or cooler bag, especially if the journey to the laboratory takes more than 30 minutes.
Before giving the glass to the laboratory assistant, let it warm up a little to room temperature (about 20-30 minutes) if it was in the refrigerator. This is necessary for certain types of analysis to be carried out correctly, for example, to correctly determine specific gravity or perform a chemical reaction with test strips.
Always inform the laboratory employee how long the sample has been in the refrigerator. This information will be indicated in the referral and will help the laboratory physician to correctly interpret the results, taking into account possible changes in the sediment.
Frequently asked questions (FAQ)
Is it possible to freeze urine for analysis?
No, it is absolutely forbidden to freeze urine for standard clinical tests. When freezing, ice crystals form, which destroy cellular structures (erythrocytes, leukocytes, cylinders), making it impossible to count them under a microscope. In addition, when frozen, the solubility of salts changes.
What to do if the urine has been left in the refrigerator for 12 hours?
It makes no sense to take such an analysis. Within 12 hours, even at low temperatures, irreversible changes occur in the sample: cells are destroyed, pH changes, bacteria multiply. The result will be false, which may lead to a misdiagnosis. It is better to collect the material again.
Do you need to shake the urine before donating it after refrigeration?
Yes, before pouring out a portion for analysis (if you collected it in a large container) or before lowering the test strip, the contents of the container must be carefully mixed. This will ensure an even distribution of sediment and cells throughout the entire volume of liquid.
Does light affect stored urine?
Yes, some components of urine, for example, urobilinogen, under the influence of light (especially solar) are oxidized and converted into urobilin, which changes the color of the sample and can distort the results. Therefore, it is better to keep the container in an opaque bag or in a dark compartment of the refrigerator.
Is it possible to store daily urine without a preservative?
Daily urine is collected in a large container for 24 hours. All this time it should be stored in the refrigerator at a temperature of +4...+8°C. If it is not possible to store such a volume in the refrigerator, a special preservative must be added to the container, which can be taken from the laboratory in advance. Without cold or a preservative, daily urine will ferment within a day.