Days Set Up
Daily, 24 hours
Analytic Time

2 hours

MiChart Code
Anti-Xa, Unfractionated Heparin
Soft Order Code

Test Updated:


Heparin, Unfractionated
Heparin, Standard
Unfractionated Heparin
Standard Heparin
UFH Anti-Xa
Anti-Xa, UFH
Heparin (UFH) Anti-Xa Assay
Anti-Xa Unfractionated Heparin
Factor Xa Inhibition
Coagulation Factor Xa Inhibition
Chromogenic Xa
Xa Chromogenic
Factor 10a Inhibition
Anti-10a UFH

Looking to order a test?

We’ve provided helpful links to make ordering easy.

Find a Requisition

All specimens should be accompanied by a requisition.

Submitting Specimens

Learn about how to properly label and where to ship specimens.

Order Kits and Supplies

MLabs provides all the supplies necessary for the collection of specimens.

Test FAQ

Visit our provider FAQ and learn about common questions to ordering tests.

Test Overview

Test Methodology

Chromogenic Substrate Assay

Test Usage

Used to monitor treatment with unfractionated (standard) heparin.

Reference Range

The therapeutic range is 0.3 - 0.7 IU/mL. Critical value: > 1.0 IU/ml.

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

Specimen Requirements

Collection Offsite

Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within one hour of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic vial, and freeze the specimen within 1 hour 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.

Blue Top Tube
Normal Volume
Full 2.7mL tube or 1mL plasma aliquot
Minimum Volume
Full 1.8mL tube or 1mL plasma aliquot

Billing Information

CPT Code
Pro Fee Code

Have More Questions?

Explore our helpful billing resources:

Our High Standard

Quality that sets us apart

As the reference laboratory division of Michigan Medicine's Department of Pathology, MLabs shares the institution's commitment to applying established quality principles to clinical laboratory testing. Like other large organizations in complex, consequential fields, we rely on an established approach to monitor quality throughout the testing process.