From Julia: Hi George, Our physicians order repeat serotonin release assay (SRA) testing on the same patients during the same hospitalization after heparin therapy has been stopped. Sometimes the physicians order within hours. We have called and asked if they are duplicates and they insist they need this testing. Is there research or literature to support ongoing monitoring of HIT with repeate SRA tests under these circumstances?
Hello, Julia, and thank you for your question. I’ve only seen EIA and SRA tests employed for HIT diagnosis, and not for subsequent monitoring, given that heparin is discontinued when HIT is present. The SRA is complex and time-consuming, and is offered by only a handful of reference facilities. The initial HIT diagnosis is generally made on the basis of the platelet count, applying either the “4T” or the “HIT Expert Probablility Score.” The physician may then follow the patient using platelet counts after switching to an alternate anticoagulant such as argatroban. I’ve seen no literature suggesting follow-up EIAs or SRAs. Here are the references for the pre-test probability score determinations:
- Lo GK, Juhl D, Warkentin TE, et al. Evaluation of pretest clinical score (4 T’s) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost 2006;4:759–65.
- Cuker A, Arepally G, Crowther MA. The HIT expert probability (HEP) Score: a novel pre-test probability model for heparin-induced thrombocytopenia based on broad expert opinion. J Thromb Haemost 2010;8:2642–50
In case I’ve missed something or your physicians are engaged in a research protocol, I’ve sent a query to some HIT experts to learn if they have seen either the EIA or SRA employed for monitoring of therapy.
Hi George, I would like to add my comment to the repeat SRA testing question by Julia. In my experience it can help to do repeat testing of the SRA or the EIA for HIT antibodies because it takes time for antibodies to develop. The first patient sample can be negative but then become positive after a day or more (not hours!). If the physician is placing multiple orders to cover himself, then the multiple orders should be spaced out over several days or a week–but clearly not over several hours. Because, as you state George, the SRA is a cumbersome and time consuming test, I would suggest repeat testing using the EIA and not the SRA. Using the EIA the OD can be followed to have a more sensitive and faster (vs the SRA) indication if the antibody titer is actually on the rise. We wrote this in our paper, Prechel, Walenga. Semin Thromb Hemostas 2008;34:86–96) where we referenced Refaai MA, AJCP 2003 and Smythe MA, J Thromb Hemost 2005.