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

Clinical Use

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

Not provided.

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.

Test Details

Methodology

Automated Analyzer (Coagulation)

Biomarkers

Activated Partial Thromboplastin Time

Analyte

aPTT

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

International Normalized Ratio (INR)

Analyte

INR

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

Prothrombin Time

Analyte

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

34529-8 - PT + aPTT Pnl PPP

Result Codes

6301-6 - INR PPP
5902-2 - Prothrombin time
14979-9 - aPTT PPP

Result Turnaround Time

1 day

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.