Cross-laboratory collaboration accelerates gold-standard SRA testing
Eye on Innovation
In a world of ever-faster technical change, Mayo Clinic Laboratories is uniquely positioned to innovate. Collaboration with clinicians pinpoints unmet patient needs and facilitates the development of diagnostic testing that provides answers.
At Mayo Clinic Laboratories, where teamwork powers innovation, a cross-laboratory collaboration has enabled implementation of a cutting-edge, gold standard test for a life-threatening condition known as HIT, or heparin-induced thrombocytopenia.
The test, a serotonin release assay (SRA), uses the expertise and technologies of the Special Coagulation Laboratory (SCL) and Clinical Mass Spectrometry Laboratory (CMSL) to guide physicians on making an accurate diagnosis of HIT, which is an important first step in choosing the best blood thinner for their patients.
“The only way we can be successful and stand out as an organization is the collaborative approach for the common good of the patient,” says Mayo Clinic hematologist Rajiv K. Pruthi, M.B.B.S, professor of medicine and co-director of the SCL.
Available in only a few other reference laboratories across the country, the functional SRA (Mayo ID: SRAU) ties together decades of Mayo Clinic experience in clinical hematology and hematopathology with the expertise and advanced testing capabilities of mass spectrometry. The test provides clear answers on whether patients are at risk for developing HIT, which claims the lives of nearly 10% of those who develop the condition.1
Since going live in mid-June, Mayo Clinic Laboratories’ SRA is on track to be ordered nearly 3,000 times annually. The popularity of the assay reflects the need for testing amongst providers when faced with the weighty decision of continuing heparin treatment in patients presenting with signs and symptoms consistent with HIT, says Anand Padmanabhan, M.B.B.S., Ph.D., associate professor and senior associate consultant in the Divisions of Hematopathology and Transfusion Medicine.
Each year millions of patients receive the blood thinner heparin for a variety of reasons, including blood clot prevention and treatment. However, more than 1% of individuals exposed to the blood thinner develop the harmful immune response.2
In those cases, the anticoagulant triggers an antibody-mediated process that activates platelets, causing patients to become hypercoagulable and at risk for life-threatening blot clots.
“It’s a disease called paradoxical thrombosis,” Dr. Padmanabhan says. “Patients may develop clotting in many parts of the body. In the legs, for example, it can lead to amputations of the toes or the entire lower part of the leg. If it occurs in other sites, like the brain, you could have a stroke. There’s a lot of morbidity associated with this diagnosis — every day, five patients die due to HIT in the U.S. alone.”
“Early recognition of HIT is extremely important,” says Dr. Padmanabhan. “The risk of a delayed diagnosis can result in a high patient mortality.”
Diagnosis is initially based on a patient’s clinical presentation and uses a scoring system known as the 4Ts, which is related to the date of onset and severity of the thrombocytopenia. The 4T scoring system is a useful clinical tool because it provides a high negative predictive value, meaning patients who score low have a low likelihood of HIT, explains Dr. Pruthi.
“But if you come up with a score that falls into the intermediate to high-risk range, then it’s a potentially serious event and you need to make some clinical decisions — generally you order the lab testing,” Dr. Pruthi adds.
Traditional HIT testing is performed through enzyme-linked immunosorbent assay (ELISA), which detects for the presence of antibodies against the heparin platelet factor.
“ELISA is really good at excluding HIT — if the test result is negative, you can pretty much tell the patient you do not have HIT and you can continue the patient on heparin,” Dr. Padmanabhan says.
The positive predictive value of ELISA, at just 30% to 50%, is not great. To confirm whether patients’ heparin antibodies are activating and will trigger HIT, a more specific test is needed.
“That test requires a high level of sophistication and is called an SRA,” Dr. Padmanabhan says.
“SRA is the gold standard assay,” Dr. Pruthi says. “Many patients who get exposed to heparin may develop the antibody, which we can measure in our labs with ELISA. But just developing the antibody doesn’t mean you’re developing the disease. You need to prove that if you have the antibody, that it is indeed a functional antibody activating platelets. The SRA assay closes the loop.”
HIT SRA testing, however, can be complicated, explains Dr. Padmanabhan. Most SRAs measure release of radioactive serotonin from activated platelets. Additionally, the assay requires a pool of fresh donor platelets.
When Mayo Clinic Laboratories leaders started work on an SRA test, the decision was made to avoid using radioactive materials, which require enhanced safety measures, specialized storage and disposal facilities, and strict oversight by the U.S. Nuclear Regulatory Commission. Instead, test developers looked toward using alternative chemicals and a testing methodology using liquid chromatography tandem mass spectrometry (LC-MS/MS).
To overcome the problem of the Special Coagulation Laboratory not housing mass spectrometry testing technology, Dr. Pruthi recruited the help of his colleague Ravinder Singh, Ph.D., director of the Clinical Mass Spectrometry Laboratory.
“This is a very serious disease, and if you can help in finding a solution, that is very good,” says Dr. Singh. “I feel very fortunate to be part of this opportunity and have the chance to learn something new and partner with another lab. With the background that we already had and in-house technology, I knew we had the capacity to absorb their volume.”
Another challenge overcome by test developers was finding an ample supply of fresh, suitable donor platelets, which are a main ingredient in the test, explains Dr. Pruthi.
“Donors are needed who are reactive to this assay, and identifying good donors was challenging because we needed a lot of samples to do the validation,” says Dr. Pruthi, adding that a small group of Mayo Clinic Laboratories employees regularly volunteered to provide platelet donations during test validation. “They were gracious enough to give us frequent samples.”
At Mayo Clinic Laboratories, the first part of SRA is performed in the SCL and involves incubation of patient serum with fresh donor platelets and heparin. This establishes whether HIT antibodies, known as anti-heparin platelet-factor 4 antibodies, activate the donor platelets to release serotonin.
The supernatant formed through platelet activation and serotonin release is transferred to the CMSL, where the serotonin is evaluated and measured using LC-MS/MS.
“With the SRA you’re measuring platelet activation, and the marker of platelet activation is the release of the platelet content (serotonin) as opposed to platelet aggregation. So it has improved specificity and it can be more sensitive than the ELISA assay,” Dr. Pruthi says.
To help coordinate testing between the labs, a dedicated Mayo Clinic Laboratories employee oversees each step of the testing process. Rachel Leger, senior developer, supervises movement of the specimen from sample receipt through result reporting and ensures each part of the test is entered properly into the Laboratory Information System database.
“This test is complicated, and we are not taking any shortcuts,” Dr. Singh says. “A lot of investment has been made to get to the right conclusion.”
Those answers are supported by the opinions and insights of Mayo Clinic Laboratories’ testing experts.
“It’s not just a result and boom, there you go,” Dr. Padmanabhan says. “It is a result accompanied by Mayo SCL physician input and expertise in cases where we think it would be beneficial for patient care, especially because HIT can be a complex problem in some patients.”
Providing confirmation to physicians on whether their patients have HIT is paramount to the laboratory leaders who implemented the assay.
“The wait and the agony that caregivers face while the SRA is pending cannot be overemphasized,” Dr. Padmanabhan explains. “I think this test is the poster child for the model of care at Mayo Clinic, where the needs of the patient come first.”
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Mayo Clinic Laboratories is committed to innovation that provides the right test at the right time for the right patients. That effort always starts with identifying gaps in patient care. Filling those gaps sometimes involves not developing new tests but finding ways to make existing tests more efficient and easier for patients.