A lithium heparin tube is a type of blood collection tube used to collect blood samples for laboratory testing. The tube contains lithium heparin, an anticoagulant that prevents clotting of the blood sample. Lithium heparin tubes allow blood samples to be collected for blood chemistry tests and other analyses that require non-clotted blood. In this article, we will discuss what lithium heparin tubes are, how they work, what tests they are used for, and some key considerations when using them for blood collection.
What is lithium heparin?
Lithium heparin is a salt composed of lithium and heparin. Heparin is a naturally occurring anticoagulant produced in the body to prevent blood from clotting. By binding to antithrombin III, heparin inhibits the coagulation cascade, preventing the formation of fibrin and blood clots. Lithium heparin is the lithium salt of heparin. It is used as an anticoagulant in blood collection tubes to prevent clotting of blood samples after collection.
Some key properties of lithium heparin:
- Rapidly binds to antithrombin III to inhibit coagulation
- Strong anticoagulant activity
- Does not significantly affect blood chemistry tests
- Available as dried coating on interior wall of blood collection tubes
When a blood sample is drawn into a lithium heparin tube, the lithium heparin coating dissolves into the blood sample, binding antithrombin III and preventing clot formation. This allows the sample to remain in liquid form for testing.
What types of lithium heparin tubes are available?
Lithium heparin blood collection tubes are available from various manufacturers in several sizes and draw volumes:
| Tube type | Tube size | Draw volume |
|---|---|---|
| Standard lithium heparin tube | 13 x 75 mm, 13 x 100 mm | 3 mL, 5 mL, 7 mL |
| Micro lithium heparin tube | 13 x 75 mm | 1.2 mL |
| Pediatric lithium heparin tube | 13 x 75 mm | 0.5 mL |
The most common size is the 13 x 75 mm tube with a 3 mL or 5 mL draw volume. The tube stopper color for lithium heparin tubes is light green.
How do lithium heparin tubes work?
When a blood sample is collected in a lithium heparin tube, here is what happens:
- Vacuum in tube draws blood sample in
- Blood comes in contact with lithium heparin coating
- Lithium heparin rapidly dissolves into blood sample
- Heparin binds antithrombin III, inactivating it
- Coagulation factors like thrombin are inhibited
- Fibrin cannot be formed, blood remains unclotted
This anticoagulant effect begins working immediately after blood is drawn into the tube. The concentration of lithium heparin is carefully calibrated to prevent clotting while minimizing impact on test results.
An additive called sodium polyanethol sulfonate (SPS) is also often included in lithium heparin tubes. SPS is an anticoagulant that works by enhancing the action of heparin. Some key functions of SPS:
- Potentiates the anticoagulant effect
- Prevents clumping of blood cells
- Inhibits complement activation
With the combination of lithium heparin and SPS, the tube provides rapid and reliable anticoagulation for blood samples.
What tests use lithium heparin tubes?
Some of the main laboratory tests that lithium heparin tubes are used for include:
Chemistry Tests
- Electrolytes (sodium, potassium, chloride)
- Kidney function tests (BUN, creatinine)
- Liver function tests (ALT, AST, bilirubin)
- Blood glucose
- Calcium
- Total protein
- Albumin
- Lipid profile
- Cardiac markers like troponin
Lithium heparin is the tube of choice for most blood chemistry analyses. The anticoagulant does not significantly affect results of these tests.
Hematology Tests
- Complete blood count
- Hemoglobin
- Hematocrit
While EDTA tubes are preferred by many labs for hematology testing, lithium heparin provides acceptable samples for most hematology assays.
Coagulation Tests
- Prothrombin time (PT)
- International Normalized Ratio (INR)
- Partial thromboplastin time (PTT)
- Fibrinogen
- D-dimer
Heparin tubes allow measurement of the intrinsic and common coagulation pathways. The tube additive does not interfere with coagulation factor assay methods.
Therapeutic Drug Monitoring
Lithium heparin tubes can be used to test blood levels of many medications, including:
- Anticonvulsants like phenytoin
- Antiarrhythmics like digoxin
- Antibiotics like vancomycin and gentamicin
- Immunosuppressants like tacrolimus
Heparin has minimal effect on these drug concentration tests.
Blood Cultures
While sodium polyanethol sulfonate can inhibit growth of some bacteria, lithium heparin tubes may be used to collect blood for blood culture analysis. However, specific blood culture collection tubes are preferred when available.
Ammonia
Lithium heparin tubes are required for measuring ammonia levels in the blood. Ammonia is an important parameter in evaluating liver function and certain metabolic disorders.
Key considerations when using lithium heparin tubes
Here are some important points to keep in mind when collecting blood samples in lithium heparin tubes:
- Fill tube completely – Underfilling tubes can lead to inaccurate test results due to improper heparin-blood ratio.
- Invert tube – Tubes should be gently inverted 8-10 times after draw to properly mix anticoagulant with blood.
- Avoid hemolysis – Hemolyzed samples can compromise test results. Avoid vigorous mixing and exposure to heat or sunlight.
- Process quickly – Some labs recommend processing lithium heparin blood samples within 2 hours of collection.
- No serum separation – Do not use lithium heparin tubes to prepare serum, as the heparin makes it impossible to form a clot.
- Correct order of draw – Heparin tubes should come after blood cultures and coagulation tubes when collecting multiple samples.
Adhering to proper collection technique helps ensure accurate and reliable test results from lithium heparin blood samples.
Conclusion
Lithium heparin blood collection tubes provide a simple, convenient way to collect non-clotted whole blood specimens for a wide variety of laboratory analyses. The heparin anticoagulant binds antithrombin III to inhibit the coagulation cascade, while sodium polyanethol sulfonate enhances the anticoagulant effect and prevents cell clumping. With proper use, lithium heparin tubes allow blood to be drawn directly into the tube and provide samples suitable for blood chemistry, hematology, coagulation, therapeutic drug monitoring, and other important clinical laboratory tests.