Nonradioactive assay helps diagnose heparin reaction

Answers from the Lab

Heparin is a commonly prescribed blood thinner that, in rare cases, triggers an immune response known as HIT. Laboratory tests that measure the release of serotonin from blood platelets can help with the diagnosis of HIT. In this test specific episode of the "Answers From the Lab" podcast, Rajiv Pruthi, M.B.B.S., describes Mayo Clinic Laboratories' new nonradioactive serotonin release assay.

“The current version of serotonin release assay that’s available in selected reference labs relies heavily on radioactive serotonin, which is very difficult to handle,” Dr. Pruthi says. “Our current generation of tests at Mayo Clinic Laboratories uses nonradioactive material and different techniques to measure the amount of serotonin released by platelets. We have had a very high degree of sensitivity and specificity with this assay.”

About 1% to 2% of patients exposed to heparin experience an immune response that causes thrombocytopenia, or low platelet count. Thrombocytopenia can lead to thrombosis, which is potentially fatal.

Diagnosis is complex because thrombocytopenia has many causes. Patients whose lplatelet counts place them at intermediate to high risk for thrombocytopenia require additional testing to determine if heparin is the cause. ELISA testing can indicate the presence of antibodies against the heparin platelet factor. But determining whether those antibodies are pathological requires a serotonin release assay.

“It’s the gold standard diagnostic test for the detection of clinically relevant pathogenic HIT antibodies,” Dr. Pruthi says.

The likelihood of a serotonin release assay detecting pathogenic antibodies is reasonably high. ELISA testing yields a number known as optical density that indicates the strength of antibody presence. An optical density below 0.4 is normal.

“If the optical density is between 0.4 and 1 — a reasonably low titer — there’s an approximately 50% chance that the antibodies are pathogenic,” Dr. Pruthi says. “An optical density between 1 and 2 has a higher likelihood of pathogenic antibodies. Above that, there is a very high likelihood that the antibodies are pathogenic.”

The serotonin release assay is used between days 5 and 14 of heparin use — the typical time frame for the development of thrombocytopenia. But Dr. Pruthi notes that HIT can develop in fewer than five days or up to four weeks after the start of heparin use.

“Our focus at Mayo Clinic Laboratories is to develop and offer clinically important tests that make a big difference in patients’ lives,” Dr. Pruthi says. “We are glad to see the serotonin release assay come to fruition.”

Listen to learn more about how Mayo Clinic Laboratories’ serotonin release assay improves upon existing versions.

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Useful information

Detecting heparin-dependent platelet activating antibodies implicated in the pathogenesis of heparin-induced thrombocytopenia.

Specimen requirements

Patient Preparation: 

  1. Specimen should be collected from a fasting (preferred, but not required) patient during an episode of suspected heparin induced thrombocytopenia.
  2. Patient should not be on ticagrelor (Brilinta) as this may interfere with the assay, yielding a false-negative result.

Supplies: Aliquot Tube, 5 mL (T465)

Collection Container/Tube: Red top (serum gel/SST are not acceptable)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: 

  1. After collection, specimen should sit at ambient temperature for a minimum of 1 hour in order to clot completely.
  2. Centrifuge and aliquot serum into a plastic vial.

Specimen Stability Information: Frozen (preferred) 2 years/Refrigerate 7 days

Performance information

Analytic time: 1 day

Days performed: Monday through Friday at various times

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Barbara J. Toman

Barbara J. Toman is a Senior Communications Specialist at Mayo Clinic Laboratories. She is also the science writer for Mayo’s Neurosciences Update newsletter, which helps referring physicians to stay informed about Mayo’s treatment and research. Barbara has worked at Mayo Clinic since 2007. She enjoys international travel and cooking.