PB2245 A SERVICE IMPROVEMENT RE‐AUDIT: THE ROLE OF THE 4T CRITERIA IN ASSESSING THE NEED FOR A HIT ASSAY IN A TERTIARY HOSPITAL SETTING

Background: Heparin‐induced thrombocytopenia (HIT) is a life‐threatening complication of exposure to heparin that occurs in a small percentage of patients exposed, regardless of the dose or route of administration which results from an autoantibody directed against endogenous (PF4) in complex with heparin. This antibody activates platelets and can cause catastrophic arterial and venous thrombosis with a mortality rate as high as 20 %. [1] Although with improved recognition and early intervention, mortality rate have been reported as below 2 %. In Saudi Arabia the use of Standard Unfractionated Heparin (UFH) is still wide spread and this is associated with a higher incidence of HIT [2]. Diagnosis of HIT relies on clinical suspicion determined by 4T score and testing for anti‐PF4/heparin antibodies. Clinical practice guidelines published by both the American College of Chest Physicians and British Society for Standards in Hematology recommended the use of the 4T score before ordering the immunoassays as a measure of pretest probability[2] [3]. Aims: The purpose of this study is to evaluate the utilization of 4T score before ordering anti‐PF4/heparin antibodies in the Hospital and to assess the impact of the 4T score would have had on the utilization of the HIT antigen test. Methods: We did a retrospective chart review for 18 years old and above inpatients admitted in King Khalid University Hospital between June 5, 2017 and December 31, 2017, and had a HIT assay performed. After calculating 4T score retrospectively which has been validated in our system, we have calculated the proportion of patients who had 4T score documented prior to Immunoassay testing. We compared the percentage of rejected orders by the hematology laboratory for the patients who does not fit the scoring system. Results: On a total of 111 patients in 205 tests were ordered by physician only 99 tests were performed due to non‐applicable test. Out of the 111 patients, 27 of the patients received Low Molecular Weight Heparin (LMWH) and the remaining received Unfractionated Heparin(UFH). None of the patients received LMWH had a positive HIT assay. Out of the 29 patients received UFH, 8 subjects had a positive HIT assay, only 1 with a low, 4 with an intermediate and 3 with high probabilities 4T scores. 2 patients developed thrombosis and one of them with intermediate probability and the other one with high probability. Summary/Conclusion: The HIT assay is still over utilized in our clinical setting even after the validation of 4T score criteria in the system 8/111(7.2%) tests were positive. Half of the patients admitted in the Intensive care units and the remaining in the general ward. Hopefully the mandating of 4T criteria in the system decrease the unnecessary HIT assay by 50 % which were rejected by the lab system. Still we are questioning the insisting of the clinical physicians in ordering the HIT assay even without calculating the 4T criteriaBy this audit, we recommend more meticulous applying for the HIT scoring system before asking the lab to do the test and this will help in more proper management with financial support to our lab system.