Proper storage of biological material is critical an important stage of laboratory diagnostics, directly affecting the reliability of the results obtained. Many patients mistakenly believe that the blood taken can sit quietly in the home refrigerator for days until they get to the laboratory, but this is a dangerous misconception.
A biochemical blood test is a complex research procedure that evaluates the concentration of various chemical elements, enzymes and proteins. Sample stability depends on many factors, including the ambient temperature, the type of tube and the presence of anticoagulants. In this article we will analyze in detail how long the biomaterial retains its properties when cooled.
Violation of the temperature regime or exceeding the permissible storage time leads to irreversible changes in the composition of the serum. Red blood cell hemolysis, a shift in the pH balance and the destruction of unstable enzymes can distort the clinical picture, which will lead to an incorrect diagnosis and the prescription of ineffective treatment.
The influence of temperature on the stability of the biomaterial
Temperature is the main factor determining the rate of biochemical reactions inside the tube after blood sampling. At room temperature, metabolic processes in blood cells continue, which leads to rapid changes in the concentration of glucose, lactate and some enzymes. Cooling slows down these processes, but does not stop them completely.
The optimal range for storing most biochemistry samples is a temperature from +2 to +8 degrees Celsius. These are the conditions provided by a standard refrigerator. However, it is important to understand that freezing whole blood (without prior centrifugation and separation) is strictly prohibited in most cases, since ice crystals destroy cell membranes.
⚠️ Attention: Freezing whole blood causes irreversible hemolysis. If you accidentally froze the test tube, the analysis cannot be performed - the results will be false due to the release of intracellular contents into the serum.
Different indicators have different sensitivity to heat. For example, glucose levels may decrease by 5-7% per hour at room temperature due to glycolysis, while the activity of some enzymes, such as LDH, may instead increase. Therefore timely cooling this is not just a recommendation, but a necessity to preserve the chemical composition of the sample.
Why can’t you store blood in the freezer?
Whole blood contains about 80% water. When water freezes, it expands, forming sharp ice crystals that pierce the walls of red blood cells and other cells. Once thawed, the blood turns into a homogeneous red liquid (haemolyzed), from which pure serum cannot be separated for analysis. Biochemical indicators in such a sample will go off scale or be completely incorrect.
Standard storage periods before testing
The time during which blood is suitable for analysis varies depending on the parameter being studied. Laboratory standards strictly regulate these intervals to ensure diagnostic accuracy. For most biochemical indicators, the maximum storage period for whole blood at a temperature of +4...+8°C is considered to be up to 24 hours.
However, there are parameters that require immediate research. These include blood gases, some hormones and electrolytes. If the analysis is not carried out within 2-4 hours, the concentration of these substances may change so much that the result loses diagnostic value. Blood serumseparated from cells by centrifugation is stored longer - up to 48 hours, and some samples up to 5-7 days when deep frozen (but this is the task of the laboratory).
☑️ Sample suitability criteria
It is important to consider the type of tube. Vacuum systems with a clot activator require time to form a clot before centrifugation. If such a tube is stored too long before separation, the cells will begin to consume glucose and secrete potassium, which will distort electrolyte balance. Therefore, the rule “the faster, the better” works flawlessly here.
Dependence of timing on the type of biochemical indicator
Not all blood components behave the same. Some substances are extremely unstable, while others can retain their structure for quite a long time. Understanding this difference helps laboratory technicians and physicians evaluate the reliability of results obtained from samples that have been stored beyond the permissible time limits.
The most sensitive to storage conditions are enzymes (ALT, AST, alkaline phosphatase) and hormones. Their activity may decrease or increase depending on the exposure time. For example, bilirubin is sensitive to light, so test tubes with it are often wrapped in foil, and enzyme concentration can change after just a few hours at the wrong temperature.
Below is a table showing the approximate periods of stability of various indicators in whole blood when stored in the refrigerator (+4...+8°C):
| Indicator | Stability (whole blood) | Stability (serum) | Special conditions |
|---|---|---|---|
| Glucose | 2-4 hours | 24 hours | Reduces quickly without preservative |
| Potassium | 2 hours | 24 hours | Increases with hemolysis |
| Bilirubin | 24 hours | 2-3 days | Keep away from light |
| Cholesterol | 24 hours | 7 days | Relatively stable |
| Creatinine | 24 hours | 48 hours | Stable |
As can be seen from the table, blood serum (liquid part after coagulation and centrifugation) is a much more stable storage medium than whole blood with cells. That is why laboratories try to separate serum from the cell mass as quickly as possible.
Rules for transporting samples to laboratory
Often a situation arises when the patient needs to independently deliver the material to the laboratory. In this case, it is he who takes responsibility for compliance temperature conditions. Simply placing a test tube in a bag with ice can be both a salvation and a cause of sample damage if you do not know the nuances.
For transportation, it is best to use special thermal containers or coolants wrapped in a towel to avoid direct contact of the test tube with ice. Direct contact may result in local freezing of the blood at the wall of the tube. Delivery time should not exceed 1-2 hours if we are talking about whole blood.
⚠️ Attention: Do not shake the tube during transportation. Mechanical shaking accelerates the destruction of red blood cells and can lead to a false increase in potassium and LDH levels in the analysis.
If you are transporting blood in winter, do not leave it in the car or outside, even if it is “cool” there. Hypothermia below zero is also fatal. In summer, on the contrary, you need to protect the sample from overheating using a thermal bag. Consistency of temperature is the key to success.
Typical errors when storing biomaterial
There are a number of common misconceptions that lead to spoilage of analyses. One of the most common mistakes is storing a test tube in the refrigerator door. The temperature there constantly fluctuates (fluctuates) due to the opening of the door, which creates unfavorable conditions for biochemical stability.
Another mistake is storing an open test tube. Evaporation of liquid leads to thickening of the blood and an artificial increase in the concentration of all substances. Also, patients often forget that the test tube must be kept in a vertical position so that the clot (if it forms) is properly separated from the serum.
Using household containers instead of vacuum systems is a gross violation. Glass jars used for medicine or food are not sterile and may contain residues that will react with blood. Only certified vacuum tubes with appropriate additives are suitable for biochemistry.
What happens to the blood if the conditions are violated
If the storage conditions have been violated, irreversible processes begin in the test tube. Hemolysis is the release of hemoglobin from red blood cells. Visually, the serum turns red. In this state, many tests, especially for hormones and enzymes, cannot be performed, since hemoglobin interferes with chemical reactions.
In addition, bacteria that enter the test tube (even in small quantities) begin to actively multiply at room temperature, consuming glucose and excreting waste products. This completely changes biochemical profile. Even in the refrigerator, bacteria do not die instantly, but only slow down their growth, so time is still limited.
Long-term storage also leads to denaturation of proteins. Protein fractions change their structure, which can affect the results of enzyme immunoassay. Therefore sample freshness is a critical parameter for high-quality diagnostics.
FAQ: Frequently asked questions
Is it possible to store blood for biochemistry in the freezer at home?
No, absolutely not possible. In a home freezer, it is impossible to control the freezing speed, which will lead to rupture of blood cells (hemolysis) and spoilage of the sample. You can freeze just frozen serum in special laboratory conditions.
What to do if the blood has been standing in the refrigerator for two days?
Most likely, such a sample is no longer suitable for most studies. Glucose, potassium and enzyme concentrations may have changed significantly. It is better to retake the test in order to get a reliable result and not treat non-existent diseases.
Does light affect the storage of blood samples?
Yes, some components, such as bilirubin and vitamin B12, are sensitive to light. It is recommended to store tubes with such samples in a dark place or wrapped in foil to avoid photo-oxidation.
Why does the laboratory refuse to accept blood taken 5 hours ago?
For whole blood, 5 hours is often the limit or has already been exceeded for many indicators. Blood cells continue to live and change the chemical composition of the environment. The laboratory is responsible for the result and cannot guarantee its accuracy on old material.