Partial Thromboplastin Time (PTT)

CPT Code(s):
85730

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 Partial Thromboplastin Time (PTT) test is clinically significant and diagnostically useful for evaluating the clotting ability of blood and diagnosing various bleeding disorders. It measures the time it takes for blood to clot in response to certain clotting factors. The specific clinical significance and diagnostic use of PTT include:

1. Assessing Coagulation Pathway: PTT evaluates the intrinsic pathway of the coagulation cascade, which involves factors VIII, IX, XI, and XII, as well as prekallikrein and high molecular weight kininogen. Abnormalities in any of these factors can lead to prolonged PTT results, indicating potential coagulation disorders.

2. Diagnosing Hemophilia and Other Factor Deficiencies: PTT is primarily used to diagnose and monitor bleeding disorders, such as hemophilia A and B. Hemophilia is characterized by a deficiency in clotting factor VIII or IX, respectively. Prolonged PTT results suggest a possible deficiency in these factors, requiring further testing for confirmation.

3. Monitoring Heparin Therapy: PTT is a critical test for monitoring patients receiving heparin therapy. Heparin is an anticoagulant medication that works by inhibiting certain clotting factors, particularly thrombin and factor Xa. PTT helps determine the appropriate dosage of heparin to maintain therapeutic anticoagulation without causing excessive bleeding.

4. Detecting Lupus Anticoagulant: PTT is also used to screen for lupus anticoagulant, an autoantibody that interferes with normal clotting mechanisms. Prolonged PTT results in the absence of other coagulation abnormalities may indicate the presence of lupus anticoagulant, which can predispose individuals to thrombosis despite the prolonged clotting time.

5. Evaluating Disseminated Intravascular Coagulation (DIC): PTT can be used as part of a panel of tests to evaluate patients suspected of having DIC. DIC is a life-threatening condition characterized by abnormal blood clotting and excessive bleeding. Prolonged PTT results, along with abnormal results from other coagulation tests, help support the diagnosis of DIC.

6. Preoperative Screening: PTT may be performed as part of preoperative screening to assess a patient's overall coagulation status and identify any underlying bleeding disorders that may increase the risk of surgical bleeding.

In summary, PTT is an important tool for assessing coagulation function, diagnosing bleeding disorders, monitoring heparin therapy, detecting lupus anticoagulant, evaluating DIC, and preoperative screening. It provides valuable information about the clotting ability of blood and helps guide appropriate management and treatment decisions for patients with coagulation disorders or those receiving anticoagulant therapy.