Red top sodium citrate tubes are used to collect whole blood specimens for coagulation testing. The sodium citrate in the tube acts as an anticoagulant, preventing the blood from clotting. Some of the most common coagulation tests performed on blood collected in these tubes include:
Prothrombin Time and INR
The prothrombin time (PT) test measures how long it takes for blood to clot. It evaluates the extrinsic pathway of coagulation. An extension of this test is the international normalized ratio (INR), which monitors patients on anticoagulant therapy like warfarin. Blood collected in a red top sodium citrate tube can be used to perform both the PT and INR tests.
Activated Partial Thromboplastin Time
The activated partial thromboplastin time (aPTT) test measures how long it takes for blood to clot via the intrinsic coagulation pathway. This test is used to evaluate patients for bleeding disorders like hemophilia. It is also used to monitor treatment with heparin. Blood collected in a red top sodium citrate tube is suitable for aPTT testing.
Fibrinogen Level
Fibrinogen is a coagulation protein that helps form blood clots. Measuring fibrinogen levels in the blood can help evaluate clotting disorders. Both low and high levels can indicate problems with coagulation. Blood collected in a red top sodium citrate tube can be used to measure fibrinogen levels using a coagulation assay.
D-Dimer
D-dimer is a protein fragment produced when a blood clot dissolves. Elevated levels indicate increased clot formation and breakdown in the body. The D-dimer test is often used to help rule out blood clots like deep vein thrombosis or pulmonary embolism. Blood collected in a red top sodium citrate tube is suitable for D-dimer testing.
Factor Assays
Coagulation factors are proteins that interact in a cascade to form blood clots. Measuring specific factor levels can help diagnose coagulation disorders. Blood collected in a red top sodium citrate tube can be used to perform coagulation factor assays for factors including:
- Factor II (prothrombin)
- Factor V (proaccelerin)
- Factor VII (proconvertin)
- Factor VIII
- Factor IX (Christmas factor)
- Factor X (Stuart-Prower factor)
- Factor XI (plasma thromboplastin antecedent)
- Factor XII (Hageman factor)
Thrombin Time
The thrombin time measures how fast fibrinogen is converted to fibrin during clot formation. This test evaluates the final step in the coagulation cascade and can help detect fibrinogen abnormalities. Blood collected in a red top sodium citrate tube can be used for thrombin time testing.
Euglobulin Lysis Time
The euglobulin lysis time evaluates the breakdown of blood clots, which involves the fibrinolytic system. Prolonged times can indicate impaired fibrinolysis. Blood collected in a red top sodium citrate tube is suitable for euglobulin lysis time testing.
Reptilase Time
The reptilase time test measures clotting factors while bypassing fibrinogen. Reptilase directly converts fibrinogen to fibrin. This test helps distinguish fibrinogen abnormalities from other coagulation disorders. Blood collected in a red top sodium citrate tube can be used for reptilase time testing.
Anti-Xa Assay
The anti-Xa assay measures the activity of low molecular weight heparins like enoxaparin and fondaparinux. This helps monitor treatment with these anticoagulants. Blood collected in a red top sodium citrate tube is suitable for anti-Xa testing.
Conclusion
In summary, red top sodium citrate tubes provide whole blood specimens for a wide array of coagulation studies. The sodium citrate prevents clotting, allowing measurement of the blood’s clotting abilities and protein factors involved in coagulation. Some of the most common coagulation tests performed on blood from these tubes include PT/INR, aPTT, fibrinogen, D-dimer, factor assays, thrombin time, euglobulin lysis time, reptilase time, and anti-Xa assays.
Collection and Handling
Proper collection and handling procedures are important to ensure quality specimens for coagulation testing. Here are some key steps:
- Use the correct tube – red top with sodium citrate anticoagulant.
- Fill the tube completely to achieve the proper blood-to-anticoagulant ratio.
- Mix the blood well with anticoagulant by gently inverting 5-10 times immediately after collection.
- Keep the specimen at room temperature after collection.
- Deliver the specimen to the lab within 4 hours of collection.
- Avoid contamination, hemolysis, and prolonged tourniquet use.
Reference Ranges
Here are typical reference ranges for some common coagulation tests performed on blood collected in red top sodium citrate tubes:
| Test | Normal Range |
|---|---|
| PT | 11-13.5 seconds |
| INR | 0.8-1.2 |
| aPTT | 23-35 seconds |
| Fibrinogen | 150-400 mg/dL |
| D-Dimer |
Reference ranges can vary by laboratory – always refer to the specific lab’s ranges for interpretation.
Limitations
While red top sodium citrate tubes are invaluable for coagulation testing, there are some limitations to be aware of:
- Results can be affected by improper fill volume, mixing, and storage.
- Sodium citrate is contraindicated in patients with severe hypocalcemia.
- Citrate can falsely prolong PT/INR results in patients with severe liver disease or disseminated intravascular coagulation.
- Cannot accurately measure platelet count or hematocrit.
- Not suitable for therapeutic drug monitoring or blood bank testing.
Advantages Over Other Tube Types
Compared to other tube types, red top sodium citrate tubes have the following advantages for coagulation testing:
| Tube Type | Advantages |
|---|---|
| Blue top citrate tube |
|
| Green top heparin tube |
|
| Lavender top EDTA tube |
|
Key Points
- Red top sodium citrate tubes provide whole blood specimens for coagulation testing.
- Sodium citrate anticoagulant prevents clotting.
- Commonly performed tests include PT, INR, aPTT, fibrinogen, factors, and D-dimer.
- Proper collection, mixing, and handling is critical.
- Results can be affected by fill volume, contamination, tourniquet time.
- Citrate can impact results in severe liver disease or DIC.
- Red tops offer advantages over blue, green, and lavender tops for coag studies.
In conclusion, red top sodium citrate tubes serve an important role in coagulation testing. When properly collected and handled, they provide quality whole blood specimens for measuring bleeding and clotting factors, coagulation times, anticoagulant monitoring, and other assessments of the body’s clotting abilities.
