Test Overview
Test Methodology

Dilution of patient's plasma with normal plasma followed by APTT and/or PT determination on the mixtures tested immediately and after 30 minute incubation at 37 C.

Test Usage

To determine reason for prolongation of the PT7 and/or aPTT test. Help to differentiate between a factor deficiency or coagulation inhibitor.

Reference Range *

Physician interpretation included.

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

Test Limitations

Performed only when APTT and PT are above the reference range. Test will not be performed if the patient is being treated with heparin, low molecular weight heparin, fondaparinux, coumadin, or a direct thrombin inhibitor (argatroban, dabigatran,bivalirudin, etc); reorder the Mixing Study two weeks after coumadin is discontinued or 48 hours after the heparins or thrombin inhibitors are discontinued.

Test Details
Days Set Up
Daily, 24 hours
Analytic Time

2 hours

Soft Order Code
MiChart Code
Mixing Study
  • Circulating Anticoagulant
  • Mixing Study
  • MIX1
  • APTT, Prolonged
  • Evaluation of Prolonged PTT
  • Prolonged PTT Evaluation
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 two blue top (citrate 3.2%) tubes. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into two plastic tubes, 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
2 full 2.7mL tubes or 2mL of plasma (two 1mL aliquots)
Minimum Volume
2 full 1.8mL tubes or 2mL of plasma (two 1mL aliquots)
Storage Temperature
Room temperature for whole blood or frozen aliquot of citrated plasma.
Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin.
CPT Code
85610, 85730
Fee Code
31105, 31106
Pro Fee CPT