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Beaumont Laboratory

Inhibitor Anticoagulant Screen

Inhibitor Screen, Circulating Anticoagulant Screen, Mixing Study, Inhibitor/Anticoagulant Screen, Antrim #26513, EPIC: LAB5194, SOFT: INACS


  • Specimens collected at Farmington Hills will be performed at Royal Oak Coagulation Laboratory.
  • Specimens with hematocrit values greater than 55% must have anticoagulant adjusted. Specimens must be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.
  • This test will not be performed on patients receiving heparin, coumadin, LMWH, or direct thrombin inhibitors.

Specimen Collection Criteria

Collect: Three Light Blue-top Becton-Dickinson 3.2% Sodium Citrate tubes.


Physician Office/Drawsite Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-26°C or 68-78.8°F) prior to transport. Transport whole blood to the Laboratory within 4 hours of collection. If transport within 4 hours is not possible, the following procedure must be followed for accurate results:

  1. Centrifuge the capped tube at 1500 x g for 15 minutes.
  2. Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
  3. Immediately remove only the top two-thirds of the PPP and transfer it into two plastic tube.
  4. Freeze (-20°C/-4°F or below) the PPP specimens immediately.
  5. Transport frozen on DRY ICE. Specimen must remain frozen during transport. 

Preparation for Courier Transport

Transport: Whole blood at room temperature (20-25°C or 68-77°F), or plasma obtained through the process listed above, frozen (-20°C/-4°F or below).

Rejection Criteria

  • Glass tubes and 3.8% Sodium Citrate tubes.
  • Specimens that are clotted or grossly hemolyzed.
  • Inappropriate specimen volume.
  • Thawed or partially thawed specimens.
  • Specimens collected from patients receiving heparin, coumadin, LMWH, or direct thrombin inhibitors.


Specimen Stability for Testing:

Whole Blood
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Platelet Poor Plasma (PPP)
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): 30 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days


Farmington Hills specimens sent to Royal Oak Coagulation Laboratory.
Royal Oak Coagulation Laboratory.
Troy Hematology/Coagulation Laboratory.


Sunday - Saturday, 24 hours a day.
Results available within 4 hours of receipt in the Laboratory. If interpretation is required, results available within 72 hours.

Reference Range

No Inhibitor detected.

Test Methodology

Light Scatter (Sysmex CA Series).


  • Prolonged PT and/or PTT which corrects upon mixing 1:1 with normal pooled plasma indicates factor deficiency. PT and/or PTT which does not correct upon mixing 1:1 with normal pooled plasma indicates inhibitor.
  • Immediate inhibitors (those which remain prolonged immediately after mixing 1:1 with normal plasma) are most often lupus-like inhibitors. All inhibitor screens that are positive for immediate inhibitor affecting the aPTT will automatically have a Platelet Neutralization Procedure (PNP) performed to prove phospholipid dependence if enough sample is available.
  • Progressive inhibitors (those which prolong further after incubation at 37°C) are most often specific factor inhibitors, such as Factor VIII inhibitors.
  • NOTE: The International Society on Thrombosis and Hemostasis (ISTH) recommends that at least two different lupus anticoagulant sensitive tests be normal before excluding the presence of a lupus anticoagulant. Furthermore, if one of these tests is positive, it should be repeated in twelve weeks to exclude a transient, clinically insignificant antibody. Diagnosis of antiphospholipid syndrome (ISTH criteria) requires laboratory evidence of an antiphospholipid antibody (anticardiolipin or beta-2 glycoprotein I of sufficient titer, or lupus anticoagulant) on two occasions at least twelve weeks apart.

Clinical Utility

This test can assist in the investigation of prolonged PT and/or PTT by the detection/differentiation of inhibitors vs. factor deficiencies. It can further aid in the differentiation of immediate (lupus-like) inhibitors from specific factor inhibitors.

CPT Code

85730x3, 85610x3. If needed: 85670, 85597, 85390

Test Codes

Antrim #26513, EPIC: LAB5194, SOFT: INACS

Last Updated


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This directory currently reflects information only for specimens collected and/or processed at the Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.