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The Serotonin Release Assay, the Gold Standard test for HIT, is now performed 5 days a week, |
Heparin-Induced Thrombocytopenia:
14C Serotonin Release Assay
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Comprehensive Coagulation menu with more than 150 tests and 20 panels
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Dedicated coagulation experts led by Mervyn Sahud, M.D. for clinical guidance and consultation
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Leading-edge innovation is further demonstrated by the development of our |
Clinical Background
HIT, a common and serious complication of heparin therapy affecting up to 5% of patients treated with heparin, has a high risk of catastrophic venous or arterial thrombosis and a high mortality rate. This adverse drug reaction is caused by the emergence of antibodies that activate platelets in the presence of heparin, leading to a reduced platelet count and paradoxically increased thrombosis. Cardiac and orthopedic surgery patients are at greatest risk for the development of HIT.
The 14C-serotonin release assay (SRA) is considered the gold standard for laboratory diagnosis because of its high sensitivity and specificity. An enzyme-linked immunosorbent assay (ELISA) detecting antibodies to the platelet factor 4 (PF4)/PVS complex offers rapid and sensitive detection, but lower specificity than the SRA. Physicians often order the 2 assays together. Quest Diagnostics offers the SRA and ELISA separately or as a panel.
Clinical Use
Diagnose heparin-induced thrombocytopenia (HIT) type II
Specific Tests
Serotonin Release Assay (SRA)
Heparin-Induced Platelet Antibody
Heparin-Induced Thrombocytopenia Panel (which includes both the Heparin-Induced Platelet Antibody ELISA and the Serotonin Release Assay)
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Performed using Fc(gamma)RIIa receptor-phenotyped platelets from highly reactive donors.
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Uses 0.1, 0.5, and 100 U of porcine heparin.
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False-positive results are excluded by running a parallel study with anti-Fc(gamma)RIIa.
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Results reported as percent serotonin release:
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Negative results are values <20%.
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Positive results are called in to the ordering physician, and consultation is available.
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Specimens with borderline results are re-tested with fresh platelets from different donor.
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ELISA
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Utilizes the PF4/PVS complex as capture antigen and an alkaline phosphatase-labeled anti-human globulin for detection antibody.
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The optical density (OD) is reported:
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OD values >0.41 are considered positive and indicate the presence of heparin-induced antibodies.
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Interpretive Information
SRA: A positive result strongly suggests HIT; consider substituting heparin with an appropriate direct thrombin inhibitor. A negative result suggests the absence of HIT.
ELISA: A positive result indicates the presence of heparin-induced antibodies but is not diagnostic of HIT; other clinical and laboratory findings should be considered prior to diagnosis. The presence of immune complexes or other immunoglobulin aggregates may cause false-positive results. A negative result suggests the absence of heparin-induced antibodies, although this assay may not detect low-titer, low-avidity antibodies.
Panel: Although SRA is the gold standard for diagnosis of HIT, caution may be warranted when interpreting discrepant ELISA and SRA results (Table 1).
Table 1. Interpretation of Heparin-Induced Platelet Antibody (ELISA)
and SRA Results in the Presence of Thrombocytopenia
SRA |
ELISA |
Interpretation |
+ |
+ |
HIT II confirmed |
- |
- |
HIT II unlikely* |
+ |
- |
HIT II likely |
- |
+ |
HIT II unlikely*† |
* Look for other causes of thrombocytopenia.
† Consider repeat SRA if clinically warranted.
Specimen Requirements
Table 2. Volume of Frozen Serum Required
Test |
Requested Volume |
Minimum Volume |
SRA |
0.5 mL |
0.25 mL |
Heparin-Induced Platelet Antibody |
0.5 mL |
0.25 mL |
Heparin-Induced Thrombocytopenia Panel |
1 mL |
0.5 mL |
Extensive online resources for healthcare professionals
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View our Coagulation Test Directory
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Visit our Interpretive Guide, for information relating to test selection, utilization, and interpretation, including heparin-induced thrombocytopenia (HIT)
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Obtain test ordering codes and specimen requirements from our online Test Menu
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Simplify test ordering and results reporting with our connectivity solutions
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References
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Newman,PM,Chong,BH: Heparin-induced thrombocytopenia-New evidence for the dynamic binding of purified anti-PF4-heparin antibodies to platelets and the resultant platelet activation Blood96:182-187, 2000.
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Kelton,JG, Smity,JW Warkentin,TE etal The Immunoglobulin from patients with heparin-induced thrombocytopenia binds to a complex of heparin and platelet factor 4 Blood 83:3232-3239,1994
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Warkentin, TE Heparin-induced thrombocytopenia:pathogenesis and management. Br J Haematol 2003;121:535-555
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Warkentin, TE. Heparin-induced thrombocytopenia: diagnosis and management. Circulation. 2004; 110(18):e454-458.
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Look KA, Sahud M, Flaherty S, Zehnder JL. Heparin-induced platelet aggregation vs platelet factor 4 enzyme-linked immunosorbent assay in the diagnosis of heparin-induced thrombocytopenia-thrombosis. Am J Clin Pathol. 1997 Jul;108(1):78-82.
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