Update Type: Reference range changed
Test Updated: 12/06/2023
Test Overview
Test Methodology

Photo-optical clot determination

Test Usage

Evaluation of intrinsic coagulation system, aid in screening for presence of classical hemophilia A and B, Christmas disease, congenital deficiencies of factors II, V, VIII, IX, X, XI and XII, dysfibrinogenemia, disseminated intravascular coagulation, liver failure, congenital hypofibrinogenemia, vitamin K deficiency, congenital deficiency of Fitzgerald factor and prekallikrein.

Reference Range *

22 - 31 seconds. If the aPTT is being used to monitor heparin, the current applicable heparin nomogram should be used.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

Blood specimens from patients treated with lytic agents usually contain heparin that adds to the prolongation of the PTT. Patients with abnormally elevated hematocrits may show falsely prolonged PTT.

Test Details
Days Set Up
Daily, 24 hours
Analytic Time

STAT 1 hour, Routine 4 hours

Soft Order Code
MiChart Code
  • Activated Partial Thromboplastin Time
  • APTT
  • PTT
  • aPTT
STAT Availability

STAT requests for this test will be performed on a STAT basis (supervisory staff approval is not required).

Specimen Requirements
Collection Instructions

Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic tube, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.

Normal Volume
Full 2.7mL tube or 1mL plasma aliquot
Minimum Volume
Full 1.8mL tube or 1mL plasma aliquot
Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin.
Additional Information

A prolonged PTT can be caused by:
A deficiency of factors I, II, V, VIII, IX, X, XI, XII, high molecular weight kininogen, or prekallikrein, Liver disease, Warfarin or heparin therapy, Fibrin degradation products, Lupus inhibitor, Specific factor inhibitors, Anticoagulant therapy with direct thrombin inhibitors (argatroban, hirudin, bilvirudin,dabigatran, etc)

CPT Code
Fee Code