Heparin-Induced Thrombocytopenia (HIT) PF4 Antibody, IgG with Reflex to Serotonin Release Assay (Heparin Dependent Platelet Antibody), Unfractionated Heparin
Ordering Recommendation

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

Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Serotonin Release Assay
1-6 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
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 
Reference Interval
Test NumberComponentsReference Interval
2012179Heparin-Induced Thrombocytopenia (HIT) PF4 Antibody, IgGLess than or equal to 0.399 OD
2005631Serotonin Release Assay (Heparin Dependent Platelet Antibody), Unfractionated HeparinNegative

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®:

Compliance Statement B: For laboratory developed tests not using a RUO kit, and for FDA approved, cleared or 510(k) exempt assays with alterations. This test was developed and its performance characteristics determined by ARUP Laboratories. The U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

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 Code(s)
Component Test Code*Component Chart NameLOINC
2012180Hep-Ind Thrombocytopenia PF4 Ab, IgG73818-7
* 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