Utilization of 4T Score to Determine the Pretest Probability of Heparin Induced Thrombocytopenia at Unity Hospital

Background:

Thrombocytopenia is common in hospitalized patients. Heparin Induced thrombocytopenia (HIT) is a life threatening condition which can lead to extensive thrombosis. Diagnosis of HIT relies on clinical suspicion determined by 4T score, and the immunoassays through testing for anti PF4/Heparin antibodies. Clinical practice guidelines published by the American Society of Hematology (2013) recommended to use the 4T score before ordering the immunoassays. If the score is less than or equal to 3, a low probability for HIT is determined, and no further testing is required. If the score is more than 3, then anti PF4/Heparin ELISA should be ordered and all heparin products should be stopped. The negative predictive value of a low probability 4T score is 99.8%, while it has a low positive predictive value (14%-64%).

Methods:

We did a retrospective chart review for patients who are 18 year or older, admitted to Unity Hospital between 07/01/2013 and 12/312014, and had anti PF4/Heparin antibodies ordered. Subjects who had confirmed diagnosis of HIT, or had ESRD on hemodialysis were excluded.

The following parameters were assessed: Age, sex, length of stay, timing of platelets drop, thrombosis, other possible causes of thrombocytopenia, previous exposure to heparin, documentation of 4T score, type of anticoagulation, Anti PF4/Heparin Antibodies result, and treatment.

After calculating the 4T score retrospectively, we calculated the proportion of patients who had 4T score documented prior to ELISA testing and proportion of ELISA tests which were not indicated due to a 4T score less than or equal to 3.

Results:

Review of 123 patients, with average age of 69.4 years, showed that testing was indicated in 18 patients (14.6%). 6 subjects had positive results, testing was indicated in all of them. 4T score was documented in 3 patients (2.4%). Of note, this may not reflect the rate of 4T score use. Some patients with thrombocytopenia may not have the test ordered due to low 4T score and would not be in our sampling frame.

Conclusions:

Anti PF4/Heparin antibodies is being overused in thrombocytopenia work up at Unity Hospital, with the fact that 85.4% of tests in this study were not indicated, costing $9,345. More conferences and lectures are needed to increase awareness among health care providers in our hospital. 4T score was added to the electronic medical records before ordering the test as a step to improve high value care and reduce unnecessary health care cost.