Lab Test

Heparin Platelet Factor 4 Antibody

Heparin/PF-4 Antibody Assay, HIT Screen, Heparin-Induced Thrombocytopenia Screen - Type II, HIT - Type II Screen, HIT, Heparin-Induced Thrombocytopenia, Heparin/Platelet Factor 4 Antibody Assay

Test Codes


Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum Whole Blood: 2.0 mL)


Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Transfer serum to a plastic transport tube and refrigerate (2-8°C or 36-46°F). (Minimum Serum: 0.5 mL)

Preparation for Courier Transport

Transport: Serum in a plastic transport tube, refrigerated (2-8°C or 36-46°F). (Minimum Serum: 0.5 mL)

Rejection Criteria

  • Specimens collected in any tube other than a plain Red-top tube.
  • Severely hemolyzed specimens.
  • Severely icteric specimens.
  • Severely lipemic specimens.
  • Specimens not collected and processed as indicated.

Inpatient Specimen Preparation

Transport specimen to the Laboratory for processing immediately after collection.

In-Lab Processing

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. If testing cannot be performed within 48 hours of collection, the serum should be frozen (-20°C/-4°F or below). (Minimum Serum: 0.5 mL)


Specimen Stability for Testing:

Red-top Tubes and Microtainers® without Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): 48 hours
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


Royal Oak Special Testing Laboratory.


Sunday – Saturday.
Sample must be received in the Special Testing Laboratory by 10:00 am for same day testing. Results available the same day as testing performed.

Reference Range

OD less than 0.4.

Test Methodology

Enzyme-Linked Immunosorbent Assay (ELISA).


Reported as negative, positive or equivocal.

The diagnosis of heparin-induced thrombocytopenia (HIT) is based on both clinical abnormalities (most commonly thrombocytopenia +/- thrombosis) AND presence of Heparin/platelet factor 4 (HIT) antibodies. If the test is positive, the OD result will be reported together with the likelihood of having a positive serotonin release (SRA) assay. The SRA is regarded as the gold standard for the lab diagnosis of HIT. In addition, OD results and follow-ups will be as follows:

 Less than 0.4  Negative – no further action taken.
 Between 0.4 and 1.99  Sample automatically sent out to Blood Center for Wisconsin for the SRA.
 Equal to or greater than 2.0  No further action will be taken because the likelihood of HIT is very high. An OD result of = 2.0
 will represent a critical value and will be called to the nursing unit or physician.

Clinical Utility

Patients receiving heparin treatment for at least a week often develop thrombocytopenia. In some cases, the platelet levels are reduced only slightly and return to normal even when heparin treatment is continued. This type of thrombocytopenia is termed "Type I" heparin-induced thrombocytopenia (HIT) and is not antibody-mediated. In other patients thrombocytopenia is more severe and is antibody-mediated. This condition is designated "Type II" HIT. Type I HIT is generally considered to be a benign condition, whereas patients with Type II HIT are at risk of developing more severe thrombocytopenia, as well as arterial or venous thrombosis if heparin is continued. Patients suspected of having HIT should have a 4 T’s score calculated and should be assessed clinically before ordering the heparin platelet factor 4 Ab.


  1. Warkentin TE, Chong BH, Greinacher A: Heparin-induced thrombocytopenia: Towards consensus. Thromb Haemost 79: 1-7, 1998.

CPT Codes

LOINC: 57761-9


Last Updated


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