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Inhibitor Anticoagulant Screen (Southeast Michigan Only)

Inhibitor Screen, Circulating Anticoagulant Screen, Mixing Study, Inhibitor/Anticoagulant Screen, Platelet Neutralization Procedure, PNP

Test Codes

EPIC: LAB1231185

Department

Coagulation

Instructions

• Specimens collected at Farmington Hills, Dearborn, Wayne, Taylor, Trenton, Troy, and Grosse Pointe 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 3.2% Sodium Citrate tubes.

TUBES MUST BE FULL.

Physician Office/Draw 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 screw cap, 5 ml, 75 x 13 mm, round base, polypropylene 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.

In-Lab Processing

Whole blood specimens must be processed as follows upon receipt in the Laboratory:

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. Test or freeze specimen according to lab protocol.

Storage

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): 5 days

Laboratory

Dearborn, Farmington Hills, Grosse Pointe, Taylor, Trenton, Troy and Wayne specimens sent to Royal Oak Coagulation Laboratory.

Royal Oak Coagulation Laboratory

Performed

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

Photo-Optical Clot Detection (IL ACL-TOP Series).

Interpretation

• 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.
  • The platelet neutralization procedure (PNP) is based on the ability of platelet phospholipid to neutralize significantly in vitro lupus anticoagulant. The disrupted platelet membranes present in the freeze-thawed platelet suspension provide the phospholipid to neutralize phospholipid antibodies present in the plasma of patients with lupus anticoagulant. The clotting time of each test plasma/saline dilution is compared to the clotting time of the test plasma/platelet dilution. A correction of 5 seconds or more between the two results is indicative of the presence of a lupus anticoagulant.
• 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 Codes

PT: 85610
APTT: 85730

If indicated:
Inhibitor PT: 85610 X2
Inhibitor APTT: 85730 X2
Thrombin Time: 85670 (X2 if Hepzyme performed)
PNP: 85597
Interpretation: 85390

LOINC:
PT: 5902-2
INR: 6301-6
APTT: 14979-9
TT: 3243-3

Contacts

Last Updated

11/1/2024