How Long Can Blood Samples Be Stored In The Fridge? Find Out

Thinking about how long a blood sample can stay refrigerated before it’s tested? Most clinical blood samples need to be tested quickly. Generally, whole blood samples collected with an anticoagulant like EDTA can last in the fridge (at 2°C to 8°C) for up to 24-48 hours for many routine tests. However, this time limit changes a lot depending on the specific test needed and how the sample was collected. How long can a blood sample stay refrigerated? It depends, but often only a day or two for best results. Maximum time blood sample refrigeration is usually limited to a few days at most for common tests, and much shorter for others. Proper blood sample storage temperature is key to keeping the sample good.

Keeping blood samples safe and sound before they get to the lab is super important. It makes sure the test results are right. Lots of things affect how long a blood sample stays good. Things like what the test is for, how the blood was taken, and what container it’s in all play a role. Putting a sample in the fridge (usually between 2°C and 8°C) helps slow down changes in the blood. But it doesn’t stop them completely. So, storing blood sample before lab delivery needs care and speed.

How Long Can Blood Samples Be Stored In The Fridge
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Why Does Storage Time Matter?

When blood is taken out of the body, changes start happening right away. Cells might break down. Chemicals in the blood might change. These changes can mess up test results.

Cells break: Red blood cells can burst, letting stuff leak out.
Chemicals change: Glucose (sugar) levels can drop as cells use it. Enzymes might become less active.
Clotting: If there’s no anticoagulant, the blood will clot, making some tests impossible.
Bacteria grow: If there are any tiny bugs in the sample, they can grow faster at warmer temps.

Putting the sample in the fridge slows these changes down. It keeps the sample more like it was when it was first taken. This helps make sure the lab gets a sample that is still good for testing. This is what we mean by sample viability refrigeration time. It’s how long the cold keeps the sample “alive” or usable for accurate tests.

Blood Sample Storage Temperature Essentials

Getting the temperature right is perhaps the most important rule for specimen storage temperature guidelines. Most guidelines say blood samples should be kept between 2°C and 8°C when stored in a fridge. This is the standard range for most lab samples.

Why this range? It’s cold enough to slow down chemical reactions and cell breakdown significantly. But it’s not so cold that it freezes the sample, which can damage cells and proteins in a different way. Freezing damages red blood cells especially badly.
Room Temperature (around 20°C to 25°C): Some tests need samples kept at room temp, but usually only for a short time, like a few hours. Many things change too fast at room temp.
Freezing (below -20°C or -80°C): Freezing is used for long-term storage of certain parts of blood, like plasma or serum, after they are separated. It stops most changes almost completely. But the initial sample should not be frozen unless specifically told to.

Always check the specific instructions for the test being done. Different tests have different needs.

How Different Sample Types Affect Storage Time

Blood samples aren’t all the same. What the lab does with the blood affects how long it lasts in the fridge.

Whole Blood

This is blood just as it came out of you, usually mixed with a chemical (an anticoagulant) to stop it from clotting.

Common Anticoagulants: EDTA (purple top tube), Heparin (green top tube), Citrate (light blue top tube).
Storage Time in Fridge (2-8°C):
- EDTA (for CBC, blood typing): Often good for 24 to 48 hours. Cell counts can change after 24 hours, but blood typing is stable longer.
- Heparin (for some chemistry tests): Usually good for 24 to 48 hours.
- Citrate (for clotting tests like PT, PTT): This is much more sensitive. Samples must get to the lab and be processed (plasma separated) very quickly, often within 4 hours of collection. Refrigeration is sometimes used temporarily after separation, but not for whole blood for these tests.
Things to know: Keeping whole blood in the fridge too long can cause red blood cells to swell or break. This can affect tests that count cells or measure certain chemicals inside cells.

Serum

Serum is the liquid part of blood after it has clotted and the cells have been removed. Blood is collected in a tube without an anticoagulant (like a red or gold top tube). It’s left to clot, then spun in a centrifuge to separate the liquid serum from the clot.

Storage Time in Fridge (2-8°C): Once separated from the cells, serum is more stable than whole blood. It can often be stored in the fridge for several days (up to 3-7 days for many common chemistry tests) before analysis.
Why more stable? Most cells are gone, so you don’t have to worry about them breaking down and releasing things into the liquid.
Longer Storage: For storage longer than a week, serum is usually frozen.

Plasma

Plasma is the liquid part of blood before it clots. It’s collected in a tube with an anticoagulant (like heparin or citrate). The whole blood is then spun down to separate the liquid plasma from the cells.

Storage Time in Fridge (2-8°C): Like serum, plasma is more stable than whole blood once separated. For many tests, it can be stored in the fridge for a few days (similar to serum, often 3-7 days).
Tests Using Plasma: Many chemistry tests, clotting tests (like PT, PTT – but remember the whole blood must be processed fast first), and specialized tests.
Longer Storage: For long-term storage, plasma is usually frozen.

Specific Test Requirements

The type of test is a huge factor in how long can blood sample stay refrigerated. Some tests measure things that are very stable, while others look for things that change quickly.

Let’s look at some common examples:

Complete Blood Count (CBC): This test counts different blood cells. It uses whole blood in an EDTA tube. Refrigeration at 2-8°C is standard. The sample is usually good for 24 hours, sometimes up to 48 hours, but cell shape and size can start changing, which might affect automated counts. Maximum time blood sample refrigeration for a CBC is often quoted as 24-48 hours.
Blood Glucose (Sugar): Glucose levels in whole blood drop over time as cells use the sugar. If the sample is left at room temperature, the drop is fast. Refrigeration slows this down. However, it’s best to spin the sample and separate the serum or plasma quickly (within 30-60 minutes) and then refrigerate it. Glucose in separated serum/plasma is much more stable in the fridge for up to 3 days. Using a special tube with a glycolytic inhibitor (like a grey top tube with fluoride) is even better for keeping glucose stable in whole blood for longer.
Potassium: Potassium is a chemical found mainly inside cells. If red blood cells break (hemolysis), potassium leaks out into the serum or plasma. This makes the result falsely high. Refrigeration can actually increase the rate of potassium leaking out of red blood cells in some samples over time, especially if the sample isn’t spun quickly. It’s best to separate serum/plasma quickly (within 2-4 hours) and then refrigerate if needed before testing.
Coagulation Tests (PT, PTT): These tests measure how fast blood clots. They use whole blood in a citrate tube. This test is very sensitive. The sample must be processed (spun and plasma separated) usually within 4 hours of collection. The separated plasma can sometimes be refrigerated for up to 24-48 hours if necessary, but testing within 4 hours is ideal. Freezing is used for longer storage.
Enzymes (like AST, ALT, CK): These are often stable in refrigerated serum or plasma for several days.
Lipids (Cholesterol, Triglycerides): Generally stable in refrigerated serum or plasma for up to several days, though triglycerides can be more sensitive.
Blood Cultures: Samples for detecting bacteria in the blood should not be refrigerated. Bacteria may not grow well in the cold. They are usually kept at room temperature and delivered to the lab quickly.
Molecular Tests (DNA/RNA): How these samples are stored depends heavily on the specific test and collection kit. Some need refrigeration, some freezing, some are stable at room temp in special preservatives. Always follow the kit’s instructions.

This shows why specimen storage temperature guidelines are so detailed and depend on the exact test. Refrigeration isn’t a one-size-fits-all solution.

Storing Blood Sample Before Lab Pickup

For samples taken at a clinic or hospital, the storage is usually well-controlled. Phlebotomists and nurses follow strict clinical blood sample storage rules. They collect the sample, label it right away, and put it in the proper storage conditions until it’s transported to the lab.

Transport: Samples are transported in special containers that keep them at the right temperature (often using gel packs for refrigeration). Speed is important to keep the sample viability refrigeration time within limits.
Logging: Labs and collection sites keep records of when samples were collected, when they arrived at the lab, and how they were stored. This helps them track if a sample might give a bad result due to storage issues.

Home Blood Test Kit Storage

More people are using home blood test kits now. These often involve collecting a small blood sample yourself, sometimes just a few drops dried on a card, or a small tube of blood collected via a fingerprick device. How to store blood sample at home from a kit is a big question.

Follow Kit Instructions EXACTLY: This is the most important rule. Home kits are designed with specific collection and storage in mind. The kit will tell you if the sample needs refrigeration or if it can be left at room temperature.
Dried Blood Spot Samples: These are very common for home kits. Blood drops are put onto a special card and allowed to air dry. Once dry, these samples are surprisingly stable at room temperature for a while. They generally do not need refrigeration. In fact, refrigerating them might introduce moisture and damage the sample. Store them in the special packaging provided, away from heat and moisture.
Liquid Samples (Small Tubes): Some home kits might involve collecting a small amount of liquid blood. The kit will usually contain a tube with a stabilizer or anticoagulant. The instructions will say how to store it. If refrigeration is required, it will say so. Place it gently in the main part of your home fridge (not the door, where temps vary more).
Keep Cool and Dry: Regardless of whether refrigeration is needed, always store the unused kit and the collected sample away from direct sunlight, heat, and humidity.
Ship Quickly: Home kits usually come with pre-paid envelopes to mail the sample back. Ship it as soon as possible after collection. Don’t leave it sitting around for days. The time it spends in transit counts towards its stability limits. The maximum time blood sample refrigeration or room temperature stability is designed to include transit time.

If the kit instructions say refrigerate, do it. If they say keep at room temp, do that. Never guess. Improper home blood test kit storage is a major reason results might be inaccurate or the lab might reject the sample.

How To Store Blood Sample At Home (If Needed Temporarily)

Let’s say you had blood drawn at a clinic, but for some reason, you are responsible for getting it to the lab, and there’s a delay. This is not ideal and should be avoided if possible, as labs prefer to handle transport from collection sites. But if you absolutely must store a standard blood sample (like a tube for a CBC or basic chemistry) at home temporarily before taking it to the lab:

Confirm if Refrigeration is Okay/Required: Ask the person who drew your blood for specific instructions for the test ordered. For many common tests (CBC, basic chemistry), refrigeration (2-8°C) is the standard temporary holding condition. For others (like clotting tests in citrate tubes, blood cultures), it might be wrong.
Use the Right Container: Keep the sample in the tube it was collected in. Do not transfer it to another container.
Refrigerate Carefully: Place the tube upright in a rack or container so it doesn’t fall over. Put it in the main body of your refrigerator, away from the door and freezer compartment. The goal is a stable 2-8°C. Your home fridge is usually in this range, but the door often fluctuates more.
Protect from Freezing: Make sure the sample isn’t touching the back wall of the fridge, which can sometimes get cold enough to freeze things. Freezing will damage the sample for many tests.
Minimize Storage Time: This is key. Even with proper how to store blood sample at home methods, the longer it sits, the higher the chance of changes. Aim to get it to the lab within 24 hours if possible. For some tests, even 24 hours is too long.
Avoid Shaking: Handle the sample gently. Don’t shake it roughly, as this can cause cells to break (hemolysis).

Again, storing clinical samples at home should only be done if there is no other option and you have clear instructions from the lab or healthcare provider on whether and how to refrigerate it based on the specific tests ordered. This is not a routine procedure and carries risks of affecting the sample quality. These are not part of standard clinical blood sample storage rules.

Factors Affecting Sample Viability Refrigeration Time

Even when stored correctly in the fridge (2-8°C), several factors can shorten how long a sample stays good:

Time Until Refrigeration: The longer a sample sits at room temperature before being put in the fridge, the more changes occur. Getting it into the cold quickly is important.
Handling: Rough handling, shaking, or exposure to extreme temperatures (hot or cold) during transport to the fridge can damage the sample.
Container Type: The material of the tube and the type of anticoagulant/preservative used are specific to the test and affect stability. Using the wrong tube will make the sample unusable quickly, regardless of temperature.
Patient Factors: Sometimes, characteristics of the patient’s blood (e.g., very high or low cell counts, certain conditions) can affect how the sample behaves during storage.
Partial Filling of Tubes: Tubes are designed to have a specific ratio of blood to anticoagulant. If a tube isn’t filled correctly, the ratio is off, which can affect stability.
Temperature Consistency: If the fridge temperature goes up and down a lot, it’s worse than a steady temperature, even if it’s in the right range.

Clinical Blood Sample Storage Rules vs. Home Storage

Professional labs and clinics follow strict clinical blood sample storage rules set by governing bodies and their own quality standards.

Validated Equipment: Labs use special lab refrigerators that maintain a very stable temperature (2-8°C) and often have temperature monitoring and alarms.
Standard Operating Procedures (SOPs): Detailed written steps explain exactly how samples are received, handled, stored, and transported.
Quality Control: Labs regularly check that their storage conditions are correct and that samples are stable for the expected times.
Traceability: Every sample is tracked from the moment it arrives. Storage conditions and times are part of this record.
Rejection Criteria: Labs have clear rules about when to reject a sample because it wasn’t stored or transported properly (e.g., clotted when it shouldn’t be, hemolyzed, wrong temperature, delayed).

Home storage lacks these controls. A home fridge temperature can vary more. There are no standard procedures or monitoring. This is why storing samples at home is risky for test accuracy and should be a last resort, guided by professional advice. The maximum time blood sample refrigeration at home should be considered much shorter and less reliable than in a lab setting.

Summary of Storage Times in Fridge (2-8°C)

Here’s a simple look at typical fridge storage times for common sample types, keeping in mind that specific test requirements can override these general guidelines.

Sample Type	Tube Type (Example)	Anticoagulant?	Typical Fridge Time (2-8°C)	Notes
Whole Blood	Purple Top	Yes (EDTA)	24 – 48 hours	For CBC, Blood Typing. Cell counts may change after 24h.
Whole Blood	Green Top	Yes (Heparin)	24 – 48 hours	For some chemistry tests.
Whole Blood	Light Blue Top	Yes (Citrate)	Keep at Room Temp initially	Must be processed (spun) within 4 hours for clotting tests.
Serum	Red/Gold Top	No	3 – 7 days	After clotting and separation. More stable than whole blood.
Plasma	Green/Light Blue	Yes	3 – 7 days	After separation from cells. More stable than whole blood.
Whole Blood	Grey Top	Yes (Fluoride)	Up to 24-48 hours	For Glucose (inhibits sugar breakdown), improves whole blood stability.
Blood Culture	Special Bottles	No	Keep at Room Temp	Do NOT refrigerate.

Note: This table gives general ideas. Always follow specific instructions for the test and collection kit. The maximum time blood sample refrigeration before testing depends on the specific substance being measured and its stability.

What Happens If Samples Are Stored Too Long?

If a blood sample is stored in the fridge for longer than it should be for a specific test, the results might be wrong.

False High Results: Chemicals leaking out of cells (like potassium from red blood cells) can make their measured levels seem higher than they really are in the body.
False Low Results: Things that get used up by cells (like glucose) can show up lower than they were originally. Enzymes can lose activity.
Inaccurate Cell Counts: Cells might change shape, swell, or break, leading to incorrect counts or identification by automated machines.
Clotting Issues: For clotting tests, if the whole blood in a citrate tube isn’t processed fast, it might start to clot, making the test impossible or giving wrong results.
Sample Rejection: The lab might notice signs of sample degradation (like hemolysis – red cells broken) and refuse to test it, meaning you have to provide a new sample.

Getting accurate test results is important for making good decisions about your health. This is why following specimen storage temperature guidelines and getting samples to the lab within the recommended sample viability refrigeration time is so crucial.

Other Storage Methods Briefly Mentioned

While refrigeration is common for temporary storage, labs also use other methods:

Room Temperature (18-25°C): Used for samples that need to be processed very quickly (like clotting tests) or for samples where refrigeration might harm the analysis (like blood cultures). Storage time is usually very short (hours).
Freezing (below -20°C, often -70°C or -80°C): Used for long-term storage of serum, plasma, or special samples. Freezing stops almost all chemical and cellular activity. Samples must be frozen quickly and thawed correctly. Whole blood is generally not frozen for routine tests because it damages the cells.

Refrigeration is a middle ground – it slows things down significantly compared to room temperature, but it doesn’t stop them completely like freezing does. This is why the maximum time blood sample refrigeration is limited.

Comprehending the Purpose of Refrigeration

The core idea behind refrigerating blood samples is simple: cold slows down chemical and biological processes. Think of food in your fridge – it lasts longer than food left on the counter. The same basic principle applies to blood samples.

Slowing Metabolism: Cells in the blood are still somewhat active after being drawn. They consume nutrients and produce waste. Cold temperatures slow down this cell activity.
Reducing Enzyme Activity: Enzymes are proteins that speed up chemical reactions. Many enzymes in blood can cause components to change. Cold temperatures reduce enzyme activity, slowing down these unwanted reactions.
Inhibiting Bacterial Growth: While not the primary reason for refrigerating standard blood samples (blood cultures are the exception), cold temperatures do slow down the growth of most bacteria that could potentially contaminate a sample.

However, refrigeration isn’t perfect. It doesn’t stop all changes. Some enzymes can still work slowly in the cold. Some cells are still prone to damage over time even when chilled. This is why there are limits to blood sample stability fridge storage.

Grasping the Limits: Maximum Time Blood Sample Refrigeration

There isn’t one single answer for the absolute maximum time blood sample refrigeration. It truly depends on what the lab is going to test for.

For common CBC or basic chemistry tests: Often 24-48 hours is acceptable.
For sensitive tests like coagulation: Whole blood is processed fast (within 4 hours); separated plasma might last 24-48 hours in the fridge.
For glucose in a plain tube: Processing within 30-60 minutes and refrigerating separated serum/plasma is best for stability over several days.
For other specialized tests: The limit could be much shorter (a few hours) or longer (up to a week for some stable analytes in serum/plasma).

Always go by the specific instructions given by the lab or your healthcare provider for the tests you are having done. If using a home kit, follow the kit’s instructions to the letter regarding home blood test kit storage. Trying to extend the sample viability refrigeration time beyond recommended limits will put the accuracy of your results at risk.

FAQ: Blood Sample Storage In Fridge

Here are some common questions people have about storing blood samples in the fridge.

H4: Can I store my blood sample in the freezer instead of the fridge?

For most routine blood tests, no. Freezing whole blood damages the blood cells and can make the sample unsuitable for many common tests like CBC or basic chemistry. Freezing is typically used for long-term storage of separated plasma or serum for specific tests, done under controlled lab conditions. Always follow the specific instructions for your sample.

H4: What happens if my blood sample gets too warm?

If a blood sample gets too warm (left at room temperature for too long, or exposed to heat), the changes that affect test results happen much faster. Cells break down faster, chemicals change quicker, and analytes might degrade. This is especially bad for tests like glucose or those looking at fragile enzymes. It can lead to inaccurate results or the lab rejecting the sample.

H4: What happens if my blood sample freezes by accident?

If whole blood freezes and then thaws, the red blood cells burst (this is called hemolysis). Hemolysis releases substances from inside the cells into the liquid part of the blood (serum/plasma). This can make tests like potassium, AST, and LDH falsely high. Freezing also affects cell counts and morphology for CBCs. Most labs will reject a frozen/thawed whole blood sample for routine tests.

H4: I have a home blood test kit. Do I put the sample in the fridge?

It depends entirely on the kit instructions. Many home kits use dried blood spots, which should NOT be refrigerated but kept at room temperature in their protective packaging. If the kit involves a small tube of liquid blood, it will specifically say if refrigeration is needed and for how long before shipping. Always read and follow the kit’s instructions carefully. Do not assume refrigeration is required or helpful for all home kit samples. This relates directly to home blood test kit storage.

H4: How long can a blood sample stay at room temperature before refrigeration?

This varies by test. For many routine tests using whole blood in EDTA or Heparin, it’s best to refrigerate within 1-2 hours of collection. For sensitive tests like coagulation (Citrate tube), the sample must be processed (spun and plasma separated) ideally within 1 hour, and definitely within 4 hours, and often stays at room temp until processing. Glucose in a plain tube should be spun within 30-60 minutes. The faster you get a sample to its proper storage temperature (either fridge or processed for freezing), the better. Storing blood sample before lab processing/refrigeration needs to be as short as possible.

H4: Why do some samples need to be kept warm (room temperature)?

Some samples, like blood cultures (to check for infection), need to be kept at room temperature because the bacteria they are looking for grow best at that temperature. Refrigeration would make it harder to detect them. Also, some tests or sample types are damaged by cold. For instance, some specialized tests on whole blood might require it to remain at room temperature.

H4: How do labs know if a sample was stored properly?

Labs rely on the information provided with the sample (time and date of collection, collection site) and visual inspection (checking for hemolysis, clots, proper fill volume). They also follow clinical blood sample storage rules during internal handling and transport. If there are doubts about the sample quality due to possible improper storage or delay, they may contact the healthcare provider or reject the sample and ask for a recollection. Adhering to specimen storage temperature guidelines is the responsibility of the sample collector and transporter.

H4: Can I reuse a blood sample that was stored too long in the fridge?

No. Once a blood sample has exceeded its recommended sample viability refrigeration time for a specific test, it should not be used for that test. Changes will likely have occurred that affect the accuracy of the results. A new sample will need to be collected.

Getting your blood drawn is just one step. How that sample is handled afterward is just as vital for getting correct test results that help you and your doctor make good decisions about your health. Always follow the instructions given by your healthcare provider or the test kit provider regarding sample storage and transport.