Definition
The plasma thrombin time test measures how quickly a clot forms when a standard amount of bovine thrombin is added to a platelet poor plasma sample from the patient and to a normal plasma control sample. After thrombin is added, the clotting time for each sample is compared with the other and recorded. Because thrombin rapidly converts fibrinogen to a fibrin clot, the test (also known as the thrombin clotting time test) allows a quick but imprecise estimation of plasma fibrinogen levels, which are a function of clotting time.
Purpose
- To detect a fibrinogen deficiency or defect.
- To help diagnose DIC and hepatic disease.
- To monitor the effectiveness of heparin or thrombolytic agents.
Procedure
Patient Preparation
- Explain to the patient that the plasma thrombin time test determines whether blood clots normally.
- Notify the laboratory and physician of drugs the patient is taking that may affect test results; it may be necessary to restrict them.
- Tell the patient that the test requires a blood sample.
- Explain who will perform the venipuncture and when.
- Explain to the patient that he may feel slight discomfort from the tourniquet and the needle puncture.
- Inform the patient that he need not to restrict food and fluids.
Implementation
- Perform a venipuncture and collect the sample in a 3 to 4.5 ml siliconized tube.
- Completely fill the collection tube and invert it gently several times to mix the sample and the anticoagulant thoroughly. If the tube isn’t filled to the correct volume, an excess of citrate appears in the sample.
- To prevent hemolysis, avoid excessive probing during venipuncture and rough handling of the sample.
- Immediately put the sample on ice and send it to the laboratory.
Nursing Interventions
- Apply pressure to the venipuncture site until bleeding has stopped.
- If a hematoma develops at the venipuncture site, apply direct pressure. If the hematoma is large, monitor pulses distal to the phlebotomy site.
- Tell the patient that he may resume any medication that was discontinued before the test is ordered.
Interpretation
Normal Results
- Adults, 140,000 to 400,000/?l (SI, 140 to 400 x 10°/L).
- Children, 150,000 to 450,000//?l (SI, 150 to 450 x 10°/L).
Abnormal Results
Prolonged Plasma Thrombin Time
- Heparin therapy
- Hepatic disease
- Disseminated intravascular coagulation (DIC)
- Hypofibrinogenemia
- Dysfibrinogenemia
- Acute leukemia
- Lymphoma
- Factor deficiency
- Shock
Interfering Factors
- Fibrin degradation products, fibrinogen, streptokinase, urokinase, tissue plasminogen activator (TPA), or heparin (possible increase).
Precautions
- To prevent hemolysis, avoid excessive probing during venipuncture and rough handling of the sample.
Complications
- Hematoma at the venipunture site.
