Sodium Heparin Tube, BD Sizes, Order of Draw, Plasma vs Serum, Tests, Stability & Sodium vs Lithium Heparin Vacutainer

Sodium Heparin Tube:

• What is Sodium Heparin Tube?
• BD Sizes
• Order of Draw
• Plasma vs Serum
• Tests Performed
• Stability
• Sodium vs Lithium Heparin Vacutainer

What is Sodium Heparin Tube?

Sodium Heparin Tubes are specialized blood collection tubes containing sodium heparin as an anticoagulant. These tubes are typically green in color and are commonly used in clinical laboratories for tests that require plasma rather than serum. Sodium heparin works by inhibiting thrombin and other clotting factors, which prevents blood from clotting after collection. This allows for immediate centrifugation and plasma separation for a variety of diagnostic assays.

These tubes are widely used in clinical chemistry, cytogenetics, toxicology, and certain molecular studies. They are especially useful when rapid turnaround time is needed, as they eliminate the waiting period required for clotting. The green stopper color coding is standardized in many laboratory systems to indicate the presence of heparin, helping to reduce errors in test processing and tube selection.

BD Sizes

BD (Becton Dickinson) manufactures Sodium Heparin Vacutainer Tubes in multiple sizes to suit various laboratory needs. Common sizes include:

• 3 mL — typically used for pediatric or small volume testing.
• 4 mL — standard for many routine laboratory tests.
• 6 mL — often used for multiple tests requiring more plasma volume.
• 10 mL — ideal for specialized tests or multiple assays from one draw.

These tubes are available in both plastic and glass formats, with plastic being more commonly used due to safety and handling advantages. The choice of size depends on the required test volume, the number of tests to be performed, and the patient’s venous access.

Order of Draw

In phlebotomy, the order of draw is crucial to avoid cross-contamination between additives that could affect test results. Sodium heparin tubes are drawn after serum tubes but before EDTA or fluoride tubes. A typical order is:

1. Blood culture bottles (sterile)
2. Sodium citrate tubes (light blue)
3. Serum tubes (red or gold)
4. Heparin tubes (green)
5. EDTA tubes (lavender)
6. Fluoride/oxalate tubes (gray)

Following this order prevents contamination of plasma or serum samples with other additives that can interfere with coagulation, chemistry, or hematology results. Correct order is especially critical for coagulation and chemistry assays.

Plasma vs Serum

Sodium heparin tubes yield plasma, which is the liquid portion of blood obtained after centrifugation without clotting. Plasma contains clotting factors, electrolytes, and other proteins, making it ideal for many chemistry and cytogenetic tests. It allows faster processing since clotting time is not required.

In contrast, serum is obtained from blood collected in tubes without anticoagulants and is allowed to clot before centrifugation. Serum does not contain fibrinogen and clotting factors, which may be preferred for certain immunology or serology tests. The choice between plasma and serum depends on the test requirements, turnaround time, and laboratory protocol.

Tests Performed

Sodium heparin plasma is suitable for a wide range of laboratory tests, including:

• Clinical chemistry panels (e.g., electrolytes, liver and kidney function tests)
• Toxicology screening and drug levels
• Hormone assays and some molecular tests
• Cytogenetic analysis, including karyotyping and FISH
• Specialized plasma-based studies requiring unclotted blood

However, sodium heparin should not be used for coagulation studies, as it interferes with clotting assays. It is also avoided in certain PCR and DNA-based tests where heparin may inhibit enzymes.

Stability

Sample stability in sodium heparin tubes depends on the analyte. Plasma should be separated promptly, ideally within 2 hours of collection, to preserve analyte integrity. At room temperature, most plasma samples are stable for up to 8 hours, and for longer storage, refrigeration or freezing is recommended.

Delays in processing can lead to hemolysis, analyte degradation, or interference from cellular metabolism. Proper inversion of tubes (usually 8–10 times immediately after collection) ensures adequate mixing of the heparin anticoagulant, preventing clot formation and ensuring accurate results.

Sodium vs Lithium Heparin Vacutainer

Both sodium heparin and lithium heparin tubes are green-top tubes, but they differ in their additive composition and suitable tests. Sodium heparin tubes contain sodium salt as the anticoagulant, whereas lithium heparin tubes use lithium salt.

Lithium heparin is more commonly used for general chemistry tests, as sodium heparin can interfere with sodium measurements, making it unsuitable for electrolyte panels. Sodium heparin tubes are often reserved for specific cytogenetic or toxicology testing where sodium interference is not a concern. Choosing the correct type is essential to avoid analytical errors, especially in electrolyte assays.