Prothrombin Time (PT) and Partial Thromboplastin Time (PTT)
Also known as: Activated Partial Thromboplastin Time (aPTT) and Prothrombin Time (PT), PT and aPTT, PT and PTT
Use
The Prothrombin Time (PT) and Partial Thromboplastin Time (PTT) test is used to assess the coagulation status of a patient. These tests are essential for diagnosing bleeding disorders, monitoring patients on anticoagulation therapy, and pre-surgical evaluations. PT measures the time it takes for blood to clot via the extrinsic and common pathways, while PTT evaluates the intrinsic and common pathways. They help to identify clotting factor deficiencies, liver disease, and the effect of anticoagulants.
Special Instructions
This aPTT test is for screening purposes only and is not intended for therapeutic monitoring. Refer to Heparin Anti-Xa [117101] and thrombin inhibitors for aPTT testing. If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.
Limitations
The test has not been validated for therapeutic monitoring of unfractionated heparin therapy, as aPTT-based therapeutic ranges for such purposes have not been established. Other limitations include reliance on specimen integrity; improper collection, handling, or anticoagulant mixture may skew results. Additionally, the presence of lupus anticoagulants and other inhibitors can affect PTT values.
Methodology
Automated Analyzer (Coagulation)
Biomarkers
LOINC Codes
- 34529-8
- 6301-6
- 5902-2
- 14979-9
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
4.5 mL, 2.7 mL, 1.8 mL
Minimum Volume
90% of full draw
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion. Mix immediately by gentle inversion at least six times.
Patient Preparation
Draw specimen one hour before the next dose of heparin if it is being administered by intermittent injection. Do not draw from an arm with a heparin lock or heparinized catheter.
Storage Instructions
Specimens stable at room temperature for 24 hours. If not tested within 24 hours, centrifuge for 10 minutes at 1500xg, transfer plasma to a frozen purple tube, freeze immediately.
Causes for Rejection
Gross hemolysis; clotted specimen; frozen specimen thawed in transit; tubes less than 90% full; improper labeling; incorrect tube type.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 24 hours |