Clinical and laboratory characteristics associated with a high optical density anti-platelet factor 4 ELISA test

Abstract

Purpose

Diagnosing heparin-induced thrombocytopenia, a potentially catastrophic immune-mediated disorder, continues to pose significant challenges for clinicians, as both clinical and laboratory tools lack specificity. There is mounting evidence supporting a positive correlation between definitive heparin-induced thrombocytopenia and optical density (OD) positivity from the widely available anti-platelet factor 4 enzyme-linked immunosorbent assays (PF4 ELISAs). However, the clinical features distinguishing these patients remain poorly understood.

Patients and methods

To better characterize this group, we conducted a case-controlled, retrospective chart review of patients from two large, urban academic institutions who underwent a PF4 ELISA at a central laboratory. Associations between OD and 18 clinical characteristics were calculated using the Fisher’s exact test for categorical variables and Wilcoxon rank-sum test for continuous variables.

Results

In total, 184 negative patients (OD <0.7), and 121 positive patients (OD >0.7), including 74 low-positive patients (0.7< OD <1.4) and 47 high-positive patients (OD >1.4) were identified. Several clinical variables were significantly different in the negative group compared with the positive group, including hospital day (P<0.001), previous admission within the past 3 months (P<0.001), and the presence of a new thrombus (P=0.003). However, many of these variables were not different between the negative and low-positive group, and were only distinct between the negative and high-positive group. When the low-positive and high-positive groups were compared, only the 4T score was significantly different (P=0.003).

Conclusion

These data indicate that those with OD >1.4 form a distinct clinical group and support the clinical utility of the 4T score.

Keywords:

• heparin-induced thrombocytopenia
• platelet factor 4 ELISA
• thrombocytopenia
• HIT
• heparin

Acknowledgments

The authors would like to thank Michael A Nardi, MS and the Bellevue Hospital Center Hematology Laboratory for their assistance in identifying, testing, and entering the sample results into the database referenced in this work. We also thank the anonymous reviewers for suggestions.

Disclosure

The authors report no conflicts of interest in this work.