Ordering Recommendation

Gold standard reflex testing for confirming diagnosis of HIT. Serotonin Release Assay is performed for positive HIT Antibody, IgG.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Serum separator tube.

Specimen Preparation

Separate from cells ASAP or within 2 hours of collection. Transfer 5.0 mL serum to an ARUP Standard Transport Tube. (Min: 2.0 mL)

Storage/Transport Temperature

CRITICAL FROZEN. Additional specimens must be submitted when multiple tests are ordered.

Unacceptable Conditions

Heparinized specimens


Ambient: Unacceptable; Refrigerated: 48 hours; Frozen: 2 years


Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Serotonin Release Assay




1-6 days

Reference Interval

Test Number Components Reference Interval
2012179 Heparin-Induced Thrombocytopenia (HIT) PF4 Antibody, IgG Less than or equal to 0.399 OD
2005631 Serotonin Release Assay (Heparin Dependent Platelet Antibody), Unfractionated Heparin Negative

Interpretive Data

This ELISA assay detects the presence of IgG antibodies to heparin-platelet factor 4 (PF4) complexes. Most cases of heparin-induced thrombocytopenia (HIT) are caused by IgG antibodies to heparin-PF4, rather than IgA or IgM antibodies. Negative results have a good negative predictive value for HIT, although rare false-negative results may occur. Positive ELISA results are sensitive but not completely specific for HIT. HIT is a clinicopathologic diagnosis. Clinical findings and the results of other laboratory tests must be taken into consideration. Higher optical density (OD) values in the IgG ELISA test correlate with a higher likelihood of positivity in platelet activation assays, such as the serotonin release assay (SRA), and an increased likelihood of clinical HIT.

A clinical scoring system to assess pretest probability of HIT along with other guidance for diagnosis is available in ARUP Consult®: https://www.arupconsult.com/content/heparin-induced-thrombocytopenia.

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Compliance Category

Laboratory Developed Test (LDT)


Microbially contaminated, heat-inactivated, hemolyzed, icteric, or lipemic sera may give inconsistent results. If Heparin-Induced Thrombocytopenia (HIT) PF4 Antibody, IgG is 0.400 O.D. or greater, Serotonin Release Assay (Heparin Dependent Platelet Antibody), Unfractionated Heparin is added. Additional charges apply.

Hotline History


CPT Codes

86022; if reflexed, add 86022


Component Test Code* Component Chart Name LOINC
2012180 Hep-Ind Thrombocytopenia PF4 Ab, IgG 73818-7
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • HAT
  • Heparin Induced Antibodies
  • Heparin PF4 Antibody
  • Heparin-Associated Antibody
  • HIPA
  • HIT Antibodies
  • HIT IgG, IgM, IgA
  • HIT PF4 Antibodies
  • HITA
  • Type II HIT
Heparin-Induced Thrombocytopenia (HIT) PF4 Antibody, IgG with Reflex to Serotonin Release Assay (Heparin Dependent Platelet Antibody), Unfractionated Heparin