Analysis of Patients Mislabeled with Heparin Induced Thrombocytopenia

Introduction: Heparin-induced thrombocytopenia (HIT) is a rare diagnosis, however commonly tested. We hypothesize that the 4T score, a diagnostic tool to diagnose HIT, is underutilized by clinicians. This may subsequently lead to unnecessary testing for HIT, administration of costly alternative anticoagulants, and mislabeling of heparin as allergy. We present preliminary data of our quality improvement study. Our aim was to analyze patients previously labeled with heparin allergy and analyze the 4T's scores, optical density values (OD), and serotonin release assay (SRA) results.

Methods: We conducted a retrospective study of patient at two tertiary care hospitals who were evaluated for HIT from October 2015- present. We were notified by pharmacy when a HIT panel was sent and alternative anticoagulation was started. Patients with unknown heparin administration from outside institutions were excluded from the study. We calculated the 4T's score and further categorized low (0-3), intermediate score (4-5), and high (6-8) score. We considered the patients to have "true HIT" if they had 4T's score > 5 or optical density values >0.4 and positive SRA.

Results: We analyzed 50 patients who were evaluated for HIT and placed on alternative anticoagulation. We observed that 64% (32/50) of the patients were listed as having heparin allergy secondary to HIT, while 36% (18/50) were not listed to have HIT as allergy on electronic health record. 19 of the 50 (38%) had scored had low 4T's score, of that two tested for HIT with a score of 0 (4%, n=50), 22 (44%) had intermediate, and 9 (18%) had high. When we utilized the 4T's score as pre-test clinical score, 0/13 patients with low score (6 not tested for SRA) and 0 /18 with intermediate score (4 were not tested) had positive SRA. 4 of the 9 (67%) high score were positive (3 were not tested). When we evaluated SRA results for patients with OD value >0.4, we observed 3 with OD value >2 and 1 with OD value of 0.798 had positive SRA. Interestingly, 1 with OD value of 2.136 had negative SRA. 8 patients with OD values > 1 had negative SRA.

Conclusion: Preliminary results show that patients are frequently tested for HIT, misdiagnosed with HIT, and mislabeled with HIT in electronic health record. When 4T's is used as clinical score, patients with low probability should not be further tested for HIT. Our study has different results for compared to study of Lo GK et al who utilized 4T's score as pre-test clinical score^{. 1}According to the study patients with low score had <5% of probability of HIT and intermediate score had 8%-29% probability of HIT. However, based on our preliminary data, none of the patients with low and intermediate score had true HIT when SRA was tested. With the intent to practice cost-effective medicine and prevent unwanted bleeding events, we plan to implement 4T score as pre-test diagnostic tool in the EMR for physicians prior to ordering alternative anticoagulation for patients with low 4T's score. We also aim to decrease hospital cost by not only preventing unnecessary HIT panel tests, but also reduce cost spent on costly alternative anticoagulation. Whether SRA is a valuable test for patients with OD values between 1-2 remains uncertain. Limitations include small sample size and incomplete chart data given retrospective study.

Reference: Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. 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.