Partial Thromboplastin Time
Also known as: PTT
Use
Partial Thromboplastin Time (PTT) is an initial test for diagnosing bleeding disorders. It evaluates the intrinsic and common coagulation pathways by measuring clotting time. The test is commonly used to investigate unexplained bleeding or clotting episodes and is often ordered to evaluate the effects of anticoagulant therapy. Abnormal PTT results may indicate a deficiency of one or more coagulation factors, or the presence of specific inhibitors like lupus anticoagulant or heparin.
Special Instructions
Patient preparation requires a sodium citrate collection tube, specified as a light blue top (Lt. Blue) tube. Immediate processing is critical: plasma must be separated from cells as soon as possible or within two hours after collection, and then frozen immediately. When multiple tests are ordered, separate specimens must be provided. Patients on heparin require more immediate handling, with centrifugation within 1 hour and limited ambient stability of 2 hours.
Limitations
The Partial Thromboplastin Time test may be affected by sample collection issues, such as improper filling of the collection tube or insufficient anticoagulation, which can lead to inaccurate results. Serum and EDTA plasma samples, as well as clotted, hemolyzed, or refrigerated specimens, are not acceptable and may lead to erroneous results. Interferences by anticoagulant medications like heparin may shorten the clotting time, restricting its use for monitoring heparin therapy. Analytical and pre-analytical factors such as improper handling or delays in processing can also influence test accuracy.
New York Approved
Methodology
Other
Biomarkers
LOINC Codes
- 14979-9
- 14979-9
Result Turnaround Time
1-2 days
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
1 mL
Minimum Volume
Not provided
Container
ARUP standard transport tube
Collection Instructions
Separate plasma from cells ASAP or within 2 hours of collection and freeze. Transfer 1 mL platelet-poor plasma to an ARUP standard transport tube.
Storage Instructions
CRITICAL FROZEN.
Causes for Rejection
Serum, EDTA plasma, clotted or hemolyzed specimens.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 4 hours (reduced to 2 hours on heparin) |
| Refrigerated | Unacceptable |
| Frozen | 2 weeks |
Other tests from different labs that may be relevant