Buzz, prospects build for heparin-induced thrombocytopenia test

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Dr. Warkentin

In his accompanying editorial, Dr. Warkentin writes that he found the conclusions of Caton, et al., “likely to be correct.” He noted that a negative result using an on-demand assay would avoid unnecessary expenses and bleeding risks “provided that the diagnostic sensitivity of the on-demand assay is sufficiently good to ensure a high negative predictive value.”
A positive result would justify the expense and risk of alternative anticoagulation “provided that the false-positive rate is not excessively high,” Dr. War-kentin wrote. (He was not involved with the development of HemosIL HIT-Ab (PF4-H), though he has received honoraria from IL, according to his editorial’s disclosure statement.)

Dr. Higgins, Bradley Brimhall, MD, and colleagues at UT Health San Antonio have been following with interest the HemosIL HIT-Ab(PF4-H) development process. “We happen to have an IL TOP instrument and realized early on that there is a tremendous amount of downstream savings to be had for a hospital in the form of decreased argatroban use, so we set out to quantify the savings,” he says.

Dr. Higgins

The HemosIL assay, like other HIT assays, is not meant to exclude HIT without knowledge of the clinical history. “HIT testing should not be ordered on patients with low pretest probability,” Dr. Higgins explains. The UT San Antonio team presented data at the Texas Society of Pathologists 2015 annual meeting that summarized their experience. They quantified the cost savings from avoiding unnecessary testing through the use of the 4Ts scoring system, a pretest probability test calculator for HIT. Utilization figures were collected over a four-year period, from 2007 to 2011. Integration of the pretest probability calculator into the hospital information system lowered annual HIT testing from 224 tests in 2007 to 67 tests in 2011, saving $18,448 annually in laboratory testing variable costs. The subsequent savings related to reduced use of argatroban were much larger. “We saved $220,055 annually by applying the 4Ts scoring system,” says Dr. Higgins.

“If we had a test like HemosIL immediately available, we estimate additional savings,” Dr. Higgins says. “The test’s utility is that it’s rapid, automated, and random access. Anyone who is trained on the machine can do the test so those savings can be realized very quickly.” Waiting two days for negative HIT test results leads to the unnecessary administration of argatroban. He estimates an additional $191,128 in annual savings if the HemosIL HIT-Ab(PF4-H) is implemented in his laboratory.

Fast-forward to July 26, 2016.

That was the day IL announced that the Food and Drug Administration granted 510(k) clearance to HemosIL HIT-Ab(PF4-H) for use on the ACL TOP Family Hemostasis Testing Systems. “Our predicate device was the ELISA, and the HemosIL HIT-Ab(PF4-H) performance is very good,” says Annie Winkler, MD, MSc, Instrumentation Laboratory’s director of medical affairs. “This assay has a negative predictive value of 99.6 percent when used within the context of the American Society of Hematology 2013 guideline, which is what is most important when you are dealing with HIT.”

The assay’s exact entry date into the U.S. market, and other key details that include pricing, have yet to be determined, but early this year remains the target. The test has been available in Europe since 2010 and in China since 2014.

Dr. Winkler believes that the HemosIL HIT-Ab(PF4-H) approval for use on the company’s ACL TOP Family of instruments will help the test come into widespread use relatively quickly. “No additional equipment is required for laboratories that already use an ACL TOP Family instrument,” she says. “HemosIL HIT-Ab(PF4-H) consists of liquid ready-to-use reagents and controls, which means that no reconstitution is required.”

Dr. Warkentin notes that, although the HemosIL HIT-Ab(PF4-H) results are expressed quantitatively, in units per mL, the results are only interpreted categorically as “positive” or “negative” based on the assay cutoff (1.0 U/mL). He would like to broaden the conversation about HIT diagnosis by including research that measures the predictive abilities of the HemosIL HIT-Ab(PF4-H) assay based on the specific quantitative result. “I have done these tests and am now analyzing the numbers,” he says. “I hope to have these results published in the near future.”

In the meantime, Dr. Warkentin calls the introduction of the assay a big deal: “This test harnesses the power of on-demand because, even in emergent situations, you can afford to wait 20 minutes to get this information,” he says. “If you have to wait eight hours, one day, three days, you will have to make treatment decisions for your patient in the meantime. That means you will be wrong some of the time, simply because you don’t have the right information when you need it.”

Dr. Refaai believes the assay has the potential to make substantial improvements in clinical outcomes associated with HIT, though he cautions that the test does have its limitations. “No assay can give 100 percent specificity and sensitivity, of course, but I would rather use an assay that can give me my answer in half an hour in accordance with the patient’s clinical picture than wait longer for some kind of perfect test,” he says. “Getting that information more quickly is what will most help me with my management of the HIT-suspected patient.”
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Darcy Lewis is a writer in Riverside, Ill.