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What is sst tube quest?

Sst tube quest is a medical procedure used to collect blood samples from veins. It involves inserting a thin, hollow needle into a vein and allowing blood to flow into an attached tube. The tube contains a vacuum that draws the blood in. Once the tube is filled to capacity, the needle is removed and the blood is sent to a laboratory for testing.

Why is an SST tube used?

SST stands for serum separator tube. These tubes contain an inert gel at the bottom that separates the blood cells from the liquid component (serum) after centrifugation. The gel forms a barrier between the clotted cells and the serum, allowing the serum to be easily extracted by piercing the divider with a sampling tool. This makes SST tubes ideal for collecting blood that will be used for certain blood tests that require serum only.

Some examples of tests that typically require serum collected in SST tubes include:

  • Liver function tests
  • Kidney function tests
  • Electrolyte tests
  • Hormone tests
  • Therapeutic drug monitoring
  • Cardiac marker tests
  • Lipid profiles
  • Blood glucose tests

The serum contains antibodies, proteins, nutrients and other useful biomarkers for assessing health and diagnosing conditions. SST tubes allow efficient separation of the serum from the blood cells so these biomarkers can be accurately measured.

What happens during an SST tube blood draw?

Drawing blood with an SST tube follows a standard venipuncture procedure with a few additional steps:

  1. The patient’s arm is cleaned with an antiseptic at the puncture site.
  2. A tourniquet is applied above the venipuncture site to engorge the vein.
  3. The phlebotomist palpates the arm to locate a suitable vein.
  4. The needle is inserted into the vein at a shallow angle.
  5. The SST tube is inserted into the needle holder and the vacuum draws blood into the tube.
  6. When the tube is full, the tourniquet is released and the needle withdrawn.
  7. The puncture site is disinfected and a bandage applied.
  8. The filled SST tube is inverted several times to mix the gel with the blood.
  9. The tube is labeled with the patient’s details.
  10. The sample is sent to the laboratory for centrifugation and analysis.

This process ensures a quality serum sample is collected for the required tests. The tubes are designed to be easily adapted to most blood collection systems.

SST tube properties that support proper blood separation

SST tubes are designed with a few special properties to enable clean and consistent serum separation:

  • Silicone coating – The tube interior has a silicone coating which acts as an inert barrier between the glass tube and the blood. This prevents activation of clotting factors and improves stability of certain analytes.
  • Gel – The gel is formulated to have a density between blood cells and serum. During centrifugation it migrates to form a stable barrier.
  • Thixotropic gel – The gel liquefies when agitated allowing it to thoroughly mix with blood initially. It then returns to gel form to maintain the separation after centrifugation.
  • Tube vacuum – The precise vacuum pressure reliably draws and holds the correct volume of blood required for testing.

These properties enable SST tubes to give high quality serum samples that are uncontaminated by blood cells and analytes are preserved in their natural state.

Recommended procedure for handling SST tubes after collection

To maintain integrity of the sample, SST tubes should be handled as follows post-collection:

  1. Invert tube 5-10 times immediately after collection – This mixes the blood with gel thoroughly so separation can occur.
  2. Allow blood to clot for 30-60 minutes at room temperature – Clotting is usually complete in under an hour so serum can be extracted.
  3. Centrifuge for 10-15 minutes at 1100-1300 RCF – This forces gel to the interface between cells and serum.
  4. Store upright to allow gel to reform barrier before analysis – Keeps serum and cells partitioned.
  5. Refrigerate if not analyzing immediately – Fridges between 2-8°C are optimal for preserving samples.
  6. Allow refrigerated tubes to come to room temperature before analysis.
  7. Pierce the gel layer carefully when pipetting serum for analysis – Insert pipette tip smoothly through the gel to avoid disturbing barrier.
  8. Perform serum extraction within 4 hours of collection for accurate results – Delays can affect lab values.

Guidelines for drawing blood into SST tubes

To obtain a proper SST tube blood sample, the following guidelines should be followed:

  • Use smallest gauge needle possible – A smaller lumen causes less cell damage so serum purity is higher.
  • Ensure tube additives don’t contaminate needle or site – Additives can interfere with tests.
  • Do not underfill or overfill tubes – Can lead to incorrect analyte concentrations from incorrect dilution.
  • Make sure tube vacuum draws enough blood – Check for adequate fill level.
  • Release tourniquet once blood starts flowing – Prevents hemoconcentration.
  • Fill tubes fully and immediately – Delays can cause blood to coagulate in needle.
  • Gently invert filled tubes 5-10 times – Ensures proper mixing of gel and blood.
  • Handle tubes with care to avoid disruption of clot and gel barrier – Clot can release fibrin strands that trap cells.
  • Follow recommended centrifugation and storage procedures – Vital for maintaining sample integrity.

Adhering to these simple guidelines helps obtain a high quality serum sample and maximize accuracy of test results.

Advantages of SST tubes

Some key advantages of using SST tubes for blood collection include:

  • Clean separation of serum and blood cells.
  • Serum can be easily extracted without contamination.
  • Samples remain stable for longer periods before processing.
  • Reduced risk of hemolysis compared to regular tubes.
  • Minimizes microclot formation.
  • Cost-effective and easy to use.
  • Standardized method for collecting serum.
  • Compatible with most laboratory analyzers.
  • Wide range of well validated tests use SST tube serum.

Disadvantages and limitations

Potential disadvantages of SST tubes include:

  • Higher cost compared to regular blood collection tubes.
  • Limited tube volume – unsuitable for some tests requiring large serum quantities.
  • Possibility of tube failure or leakage.
  • Potential for microclots if tube not inverted properly after collection.
  • Separation gel can be disturbed if handled roughly.
  • Less suitable for whole blood analysis or cellular studies.
  • Requires prompt centrifugation and processing.
  • Not ideal for pediatric patients with low blood volumes.

Troubleshooting issues with SST tubes

Some potential issues that may arise with SST tube sampling and how to troubleshoot them:

Issue Possible Causes Troubleshooting
Incomplete separation of blood and serum
  • Low centrifugation force
  • Short centrifugation time
  • Tube not centrifuged promptly
  • Centrifuge at higher RCF for longer duration
  • Spin samples promptly after allowed clotting period
Small clot in serum
  • Aggressive pipetting of serum
  • Dislodged gel barrier
  • Fibrin strand formation
  • Use caution when pipetting serum
  • Visually inspect gel barrier integrity after centrifugation
  • Increase centrifugation time to compact clot
Low serum yield
  • Overfilled tube
  • Underfilled tube
  • Defective tube
  • Adhere to tube fill range
  • Inspect tube filling during collection
  • Check tube and needle functioning

Following SST tube collection guidelines closely and being aware of potential issues can help avoid many problems and improve serum preparation quality.

Special considerations for SST tubes

Some special considerations when using SST tubes include:

  • Anticoagulants – SST tubes contain clot activator so anticoagulants can interfere. Draw SST tube before tubes containing anticoagulant if collecting multiple tubes.
  • Order of draw – Recommended order is blood cultures > SST/serum > heparin > EDTA. This prevents cross-contamination.
  • Volume – Underfilling tubes risks imprecise dilution while overfilling can burst tube. Use correct size tubes for required volume.
  • Inverting – Immediately inverting filled tubes 5-10 times is crucial to activate clotting and mix thoroughly with gel.
  • Pediatric patients – May require prioritization, smaller needle gauges, and tubes with lower draw volumes.
  • Anticoagulant therapy – May delay clotting so increase inversion and centrifugation time.
  • Hemolysis – Can cause analyte deterioration. Draw gently, release tourniquet promptly.
  • Lab storage – Transfer serum to secondary tubes if storing over 24 hours. Maintain at refrigerated temperatures.

Understanding these aspects helps maximize the quality of the serum sample obtained from SST tubes.


SST tubes are widely used in healthcare to provide quality serum samples for blood testing. Their specialized gel separation design offers a simple and standardized way to separate serum from whole blood. However, proper technique is important when collecting and handling SST tubes to gain the full benefits. Following best practices for venipuncture, sample mixing, centrifugation and storage preserves sample integrity and provides laboratories with an optimal serum specimen for analysis. With appropriate use, SST tubes can streamline workflow and improve the accuracy of serum biochemical testing and therapeutic drug monitoring for better patient care.