Grey blood bottles, also known as serum tubes or separator tubes, are an essential part of the blood collection process. They are used to collect blood samples for a variety of medical tests and procedures. But what exactly are grey blood bottles and what makes them different from other types of blood collection tubes?
What Are Grey Blood Bottles?
Grey blood bottles, as their name suggests, are blood collection tubes with grey rubber stoppers that are made of glass or plastic. The most distinctive feature of these tubes is the presence of a gel or other separator material in them. This material acts as a barrier between the blood cells and the serum after collection.
The separator is composed of an inert polymer gel such as polyester gel. It has a density that is intermediate between the lighter serum fraction and the cellular fraction of blood. This allows the blood to separate into different layers during centrifugation.
The tube contains silica particles that activate the clotting process when blood is drawn into the tube. This leads to clot formation. The clot then settles at the bottom of the tube during centrifugation, below the separator gel.
Composition of Grey Blood Bottles
- Rubber stopper
- Separator gel
- Silica particles as clot activator
- Tube material – glass or plastic
Unlike other blood collection tubes, these separator tubes contain thixotropic gel and clot activator that allows clean and quick separation of blood fractions. This makes them ideal for collecting samples for serum-based tests.
Why are Grey Blood Bottles Used?
Grey blood bottles serve some important purposes:
Allow Separation of Blood Components
The separator gel in these tubes allows clean separation of the blood sample into different fractions during centrifugation. The gel forms a stable barrier between the serum and cellular fractions of the blood.
Provide Serum for Analysis
These tubes are used when serum is required for analysis, instead of plasma. The clot activator induces clot formation, separating serum from the cellular fraction.
Prevent Contamination from Blood Cells
The separator gel acts as a physical barrier, preventing the lighter serum from getting contaminated by the heavier blood cells beneath it. This allows clean and uncontaminated serum collection.
Maintain Sample Integrity
The gel barrier maintains the chemical integrity of the separated blood fractions. There is no contamination or interaction between the separated layers.
Enable Processing of Different Blood Fractions
The separator allows simultaneous processing of the distinct blood fractions from a single sample collection. The serum can be used for clinical chemistry testing, while the blood cells may be used for hematology testing.
When are Grey Blood Bottles Used?
Grey blood bottles are used in the following situations:
When Serum is Required for Analysis
These tubes are used when serum is specifically required as the sample for biochemical testing and clinical chemistry. The clot activator present induces clot formation to obtain serum.
Routine Blood Tests
They are widely used during general health checkups and routine blood tests where serum needs to be separated from the blood cells before testing.
Therapeutic Drug Monitoring
Grey blood bottles are used when performing therapeutic drug monitoring to measure medication levels. The serum provides an accurate sample for determining drug concentrations.
Infectious Disease Testing
These tubes can be used when testing for infectious diseases like HIV, hepatitis, and syphilis. Serum provides a suitable sample for such blood tests.
Metabolic Panel Testing
They are the tube of choice when doing metabolic panel testing to assess organ function. The serum can be accurately tested for levels of metabolites and enzymes.
Toxicology Screening
Grey blood bottles provide the ideal sample for toxicology screening to detect presence of ingested toxins and drugs of abuse.
What Types of Tests use Grey Blood Bottles?
Some common medical tests that use grey blood bottles for sample collection include:
Liver Function Tests
LFTs or liver function tests like ALT, AST, bilirubin rely on serum samples. Grey blood bottles are used to separate serum for assessing liver function.
Renal Function Tests
Tests like BUN and creatinine that indicate kidney function are done on serum samples collected in these tubes.
Electrolyte Panel
These tubes can be used when ordering an electrolyte panel to determine blood sodium, potassium, chloride levels.
Cholesterol Testing
Cholesterol tests like total cholesterol, HDL, LDL, and triglycerides require serum samples obtained via separator tubes.
Hormone Tests
Hormonal tests like TSH, FSH, LH utilize the serum derived from grey blood bottles.
Blood enzymes tests
Separator tubes are ideal for estimating blood levels of enzymes like amylase, lipase, and CK.
Serological Testing
These tubes provide the serum needed to carry out serological tests for infectious diseases and immunity.
Therapeutic Drug Monitoring
Medication levels of drugs like antibiotics, anti-seizure drugs, and immunosuppressants can be measured using serum samples collected in grey tubes.
Toxicology Screening
The serum acts as an appropriate sample for toxicology screens to detect toxins, drugs, and alcohol.
How to Use Grey Blood Bottles
Using grey blood bottles appropriately is vital for collecting quality serum samples. Here are some tips on using them:
Choose the Right Tube Size
These tubes come in different sizes like 5 mL, 7 mL, and 10 mL. Choose the appropriate tube size based on the volume of blood sample required.
Collect the Sample Correctly
Blood should be collected by venipuncture and allowed to fill the tube up to its indicated fill volume to ensure the correct blood-additive ratio.
Invert Tube Gently
Once filled, gently invert the tube 8-10 times to mix the clot activator with the blood to initiate clotting.
Allow Adequate Clotting Time
Keep the tube upright for 30-60 minutes for complete clot formation and separation of serum from cellular fraction.
Centrifuge Promptly
After clotting, centrifuge the separator tube as soon as possible at the speed and time specified.
Store Properly
Once centrifuged, store the serum by carefully transfer it to a clean storage tube without disrupting the gel layer.
Handle Carefully
Avoid shaking, inverting or agitating the tube post-centrifugation as this can disrupt the separator gel leading to remixing of fractions.
Maintain Upright Position
Always keep the tube upright once centrifuged so as to not disturb theSeparator gel barrier.
Advantages of Grey Blood Bottles
Some benefits offered by serum separator tubes:
Single Collection Tube for Whole Blood
Eliminates need for collecting blood in multiple tubes since whole blood fractions can be obtained from one grey top tube.
Enhanced Sample Quality
The gel separator provides contamination-free, undamaged serum and blood cell samples for analysis.
Rapid Turnaround Time
Allows quick separation of serum from blood cells, enabling faster test results.
Better Sample Stability
Maintains integrity and stability of separated samples for longer duration before analysis.
Leak-proof Separation
The hydrophobic separator gel provides a leak-proof barrier between serum and blood cell fractions.
Flexibility in Handling
Samples can be transported over short distances without remixing or contamination.
Cost-effective
Single tube collection of whole blood reduces need for purchasing additional vacutainers.
Universal Application
Suitable for wide range of blood tests and analyses that use serum sample.
Limitations of Grey Blood Bottles
Grey blood tubes also have some limitations:
Limited Shelf Life
They have shorter shelf lives compared to other tubes. The separator gel can deteriorate over time.
Delayed Testing
Testing cannot begin immediately and is delayed due to the need for clotting and centrifugation.
Contamination Risk
Careful handling is vital as there is risk of cross-contamination between separated layers if gel barrier is disrupted.
Special Centrifugation Needs
These tubes require relatively high centrifugal force and proper centrifugation technique.
Tube Composition Issues
Plastic tubes may absorb some analytes while serum stored in glass tubes can develop microclots over time.
Costlier Than Plain Tubes
Separator tubes are more expensive than regular blood collection tubes.
Limited Uses
Can only be used for analyzing serum samples, not whole blood.
Conclusion
Grey blood bottles or separator tubes are specially designed to allow clean and convenient separation of serum from whole blood samples. The presence of a gel barrier enables collection of high quality serum, uncontaminated by blood cells. This makes grey blood bottles ideal for serum biochemical tests and analyses where cellular components can interfere. However, proper technique during centrifugation and storage is vital to maintain integrity of the separated samples. Overall, grey top tubes serve as an indispensable tool in collection of blood for serum-based clinical laboratory testing.