Prothrombin Time (PT/INR)
CPT Code(s):
85610
Turnaround Time:
2 hours
Specimen Requirements
Preferred Specimen:
Plasma
Minimum Volume:
2.7 mL
Transport Container:
Light Blue Top Tube
Transport Temperature:
Frozen
Collection Instructions:
Whole blood collected in Blue - top Sodium Citrate tube (3.2%); filled to completion. Sample should be gently inverted 5 - 6 times to mix anticoagulant with blood. Centrifuge, pipette off plasma, and freeze for transport.
Rejection Criteria:
Gross hemolysis; clotted specimen; frozen specimen thawed in transit; tubes <90% full; improper labeling; specimen collected in tube other than 3.2% citrate.
Stability Criteria
Room Temperature:
2 hours
Refrigerated:
4 hours
Frozen:
48 hours
Clinical Significance
The PT/INR (Prothrombin Time/International Normalized Ratio) test is a clinically significant diagnostic tool used to assess the clotting ability of a patient's blood. It measures the time it takes for blood to clot and provides valuable information about the patient's coagulation status. The specific clinical significance and diagnostic use of the PT/INR test include:
1. Monitoring Anticoagulant Therapy: The PT/INR test is commonly used to monitor patients who are receiving anticoagulant therapy, such as warfarin. Warfarin inhibits the production of clotting factors in the liver, leading to an increase in the PT and prolongation of clotting time. By regularly monitoring the PT/INR, healthcare providers can adjust the dosage of anticoagulant medications to maintain the desired therapeutic range and prevent complications associated with over- or under-anticoagulation.
2. Evaluating Liver Function: The PT/INR test is sensitive to liver dysfunction, as clotting factors are produced in the liver. Patients with liver diseases, such as cirrhosis or hepatitis, may have impaired clotting ability, leading to an increased PT/INR. Monitoring the PT/INR in these patients helps assess liver function and determine the severity of liver disease.
3. Diagnosing Bleeding Disorders: The PT/INR test is also used to diagnose bleeding disorders, such as hemophilia or von Willebrand disease. These conditions are characterized by deficiencies or abnormalities in specific clotting factors, leading to prolonged clotting times. By evaluating the PT/INR, healthcare providers can identify potential bleeding disorders and guide further diagnostic investigations or treatment.
4. Assessing Risk of Thrombosis: In some cases, a decreased PT/INR may indicate a higher risk of thrombosis or blood clot formation. This can be seen in conditions such as Factor V Leiden mutation or other inherited clotting disorders. By monitoring the PT/INR, healthcare providers can identify patients at risk of developing abnormal blood clots and implement appropriate preventive measures or treatment.
5. Guiding Surgical or Invasive Procedures: Prior to surgical or invasive procedures, the PT/INR test is often performed to assess a patient's bleeding risk. It helps determine whether the patient's clotting ability is within the desired range to minimize the risk of excessive bleeding or clotting complications during the procedure. Based on the PT/INR results, healthcare providers can make informed decisions regarding the timing of the procedure and the need for any preoperative interventions or adjustments in anticoagulant therapy.
In summary, the PT/INR test plays a vital role in clinical practice for monitoring anticoagulant therapy, assessing liver function, diagnosing bleeding disorders, evaluating thrombotic risk, and guiding surgical or invasive procedures. It provides valuable information about a patient's clotting ability, helping healthcare providers make informed decisions about treatment, dosage adjustments, and overall patient care.