Utility of consecutive repeat HIT ELISA testing for heparin‐induced thrombocytopenia

Abstract

Heparin‐induced thrombocytopenia (HIT) is a serious complication of heparin therapy. Limited data are available regarding repeat HIT antibody testing after an initial negative test. We conducted a retrospective study to determine the utility of repeat testing. Heparin antibodies were detected using the GTI‐PF4 enzyme‐linked immunoabsorbent assay, ELISA (GTI Diagnostics, Waukesha, WI). Patients (n = 137) were assigned to one of three groups based upon the initial negative test optical density (OD) range of low = 0–0.132, medium = 0.133–0.267, and high = 0.268–0.399. A pretest clinical score was retrospectively determined using the “4T's” (Thrombocytopenia, Timing of platelet fall, Thrombosis, and the absence of oTher causes of thrombocytopenia). A subsequent positive ELISA was found in 16% (22/137) of patients who underwent repeat testing. Most of these patients had a low pretest clinical score (62%). Four patients had an interval change in the pretest score between the initial negative and subsequent positive tests. Only these four patients developed HIT with thrombosis (HITT). Eighty percent of patients with a high initial negative test OD value had a positive ELISA on repeat testing; however, the initial negative test OD value could not predict whether a patient developed HITT. In contrast, an increase in the pretest clinical probability between initial and repeat testing better predicted HITT. Consecutive repeat ELISA testing for heparin antibodies may be warranted in patients with an increase in their pretest clinical score after an initial negative test as an adjunct to confirm the diagnosis of HIT. Am. J. Hematol., 2008. © 2007 Wiley‐Liss, Inc.

Heparin-induced thrombocytopenia during extracorporeal life support: incidence, management and outcomes

“…As shown in our study, there is limited accord between H-PF4 ELISA screening results and confirmed HIT cases for patients on ECLS (3). Furthermore, HIT may still be present in patients on ECLS despite negative testing (5,33). According to our analysis, the SRA was positive only in 32% of clinically confirmed HIT, which may indicate that the test may not be specific enough.…”

Correlation of Bivalirudin Dose with Creatinine Clearance During Treatment of Heparin‐Induced Thrombocytopenia

“…One retrospective analysis reported that an initially negative PF4 test converting to a positive result was associated with thrombosis only if the 4T score increased in a concurrent fashion. 20 Also, ELISA optical density values for PF4 antibodies were not reported during this time frame, and these data may help predict thrombotic risk in isolated cases of HIT. 21 Finally, because it was not locally available, the serotonin release assay (a potentially confirmatory laboratory test) was not performed.…”

Heparin-Induced Thrombocytopenia: An Update

“…41 However, when the suspicion of HIT is high based on clinical symptoms one negative test should not rule out HIT, as a subsequent test is often positive. 82,83 There are also frequent reports of platelet-activating antibodies being present in HIT ELISAnegative specimens. 32,34,59,72,83 The interpretation and value of HIT-diagnostic tests vary with timing of collection of the patient specimen, as well as with the clinical status of the patient.…”