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Introduction: Heparin induced thrombocytopenia (HIT) is a serious prothrombotic condition, usually triggered by exposure to heparin products with formation of antibodies to platelet factor 4/ heparin polyanion complexes. Diagnostic algorithm for HIT combines clinical scoring (4T score) with time sensitive screening for HIT antibodies (HIT-ab), while serotonin release assay (SRA) is remains the gold standard for confirmatory diagnosis. The rate of utilization of 4T score was low in our institution, resulting in inappropriate orders for HIT-Ab test and subsequent administration of unnecessary alternative anticoagulation (AC) in patients with false positive results. In this project, we designed a structured HIT diagnostic workflow incorporating 4T score calculation in our electronic medical record (EMR) and replaced particle immunofiltration assay (PIFA) with latex immunoturbidometric assay (LIA) in our laboratory for HIT-Ab screening, with an aim to improve the rate of 4T utilization and accuracy of HIT diagnosis in a cost-efficient manner. Methods: In phase I, we performed a retrospective chart review of all patients with PIFA ordered between March 2017-March 2018. Two investigators independently calculated 4T, collected data on results of HIT-Ab, confirmatory SRA tests, and the duration of alternative AC from each record. Any variations in 4T score were resolved by a senior investigator. In phase II, we implemented a new workflow in the EMR incorporating mandatory calculation of 4T score with every order for HIT-Ab test. Our lab started using LIA in place of PIFA. Charts were reviewed on patients with HIT-Ab orders (LIA) from January-June of 2019. Results: On review of data from phase I, we noted that 4T score was documented in only 5 (0.02%) of 170 patients in whom a PIFA test was ordered. Per investigators assessment, 113 (66.4%) patients had low probability (4T ≤ 3), 47 (27.6%) had intermediate probability (4T 4 or 5), and 10 (5.8%) had a high probability (4T ≥ 6) for a diagnosis of HIT. SRA was ordered in 32 patients, although 17 of them had low probability per investigator assessment. PIFA test came back positive in 26 patients, of whom 16 had corresponding SRA results, and three samples were positive for SRA. PIFA was negative in two patients with confirmed HIT (SRA positive). A total of 19 patients received alternate AC in the first phase, 7 of them had low 4T score per our assessment. In phase II, 69 records were found with available LIA results, showing a relative decrease in HIT-Ab orders compared to earlier phase at the six months mark. Documentation of 4T score has been 100% by ordering physicians, a certain improvement from phase I. Investigator calculated 4T score showed low probability in 33 (47.8%) patients, intermediate probability in 31 (44.9%) patients, high probability in 5 (0.07%) patients. LIA was positive in 7 of the 69 ordered tests, 6 of whom scored high/intermediate in the 4T score. HIT diagnosis was confirmed in 3 of these 7 patients with a positive SRA result. During this period, all the 7 of the eight patients who received alternate AC had a high or intermediate probability for HIT as per 4T. Conclusion: Our study demonstrated that the successful implementation of a structured protocol for HIT diagnosis ensured 100% adherence to the calculation and documentation of 4T score by clinicians, and significantly reduced the number of inappropriate HIT-Ab test orders in our institution. Use of alternate AC was also more consistent with the level of probability for HIT. Table Disclosures No relevant conflicts of interest to declare.

Introduction: Heparin induced thrombocytopenia (HIT) is a severe prothrombotic condition, usually triggered by exposure to heparin products. It is characterized by platelet activation induced by the formation of antibodies to the platelet factor 4 (PF4)/ heparin polyanion complexes. Diagnostic algorithm includes clinical scoring (4T score) alongside serological test for detection of these antibodies (HIT-Ab), while serotonin release assay (SRA) remains the gold- standard for confirmation. The automated latex immunoturbidometric assay (LIA) has recently been FDA approved as a screening tool for HIT and is a potential alternative to the conventional particle immunofiltration assay (PIFA) for time-sensitive detection of HIT-Ab to guide treatment considerations. We recently introduced LIA in our institution. In this study, we present our experience with LIA in comparison to PIFA in the diagnosis of HIT. Methods: We retrospectively reviewed the charts of all the patients on whom a PIFA was ordered between March 2017 and March 2018 in our hospital. We collected information on the results of the PIFA and SRA (if available). We replaced PIFA with LIA for HIT screening. Then, we introduced a structured protocol for diagnosis of HIT in our institution by incorporating 4T scoring alongside LIA order in the electronic medical record (EMR), in December 2018. We reviewed the EMR of all the patients on whom HIT-Ab test (LIA) was ordered between January and June of 2019, and collected similar information as before. All the data were compiled in a single master excel sheet for calculation of performance characteristics (sensitivity, specificity, positive and negative predictive values) for both PIFA and LIA. A patient was considered to have the diagnosis of HIT if the result of SRA was available and positive. Results: In the first phase, a total of 31 orders for SRA was noted against 170 PIFA orders. Five patients had a positive SRA, of whom two were PIFA negative. Half the patients with a negative SRA result were positive for PIFA. Hence, the sensitivity and specificity of PIFA test for our study population were noted to be 60% and 50%, respectively. PIFA had a positive predictive value (PPV) of mere 18.75% for the diagnosis of HIT, whereas the negative predictive value (NPV) was found to be 86.66%. Introduction of structured protocol for HIT diagnosis substantially reduced the number of inappropriate SRA orders in the second phase. On review of data for six months with the new HIT-Ab test LIA, SRA was ordered in only eight patients, to go with 69 orders for the LIA. The result of LIA was positive in all three patients with a positive SRA, whereas it was false positive in four instances. Only one patient was negative for both LIA and SRA during this period. LIA was found to be 100% sensitive and 20% specific for the diagnosis of HIT in our sample. PPV and NPV for LIA were 42.85% and 100%, respectively. Conclusion: The sensitivity and specificity of LIA were found to be 100% and 20%, respectively, in our study population, which is different from the earlier report (Warkentin et al. 2017). The small sample size is a limitation of our study. Higher PPV and NPV for LIA, with its quick turnaround time, make it a useful alternative for the time-sensitive determination of post-test probability for HIT in patients. [HIT- Ab- Heparin Induced Thrombocytopenia Antibody, PIFA- Particle Immunofiltration Assay, LIA- Latex Immunoturbidometric Assay, SRA- Serotonin Release Assay, +ve- Positive, -ve - Negative, PPV- Positive Predictive Value, NPV- Negative Predictive Value] Disclosures No relevant conflicts of interest to declare.

Background The standard practice for diagnosis of heparin-induced thrombocytopenia (HIT) involves a combination of 4T score and laboratory tests, such as enzyme immunoassay for detection of antibodies. We noted a lack of widespread use of 4T score in our practice setting. We also found that our laboratory utilized Particle Immunofiltration Assay (PIFA) for HIT screening, which has been shown to have questionable diagnostic utility in HIT diagnosis (Warkentin et al., 2007). The study aims to improve the rate of 4T score usage in conjunction with an improved laboratory diagnostic test for patients with suspected HIT in a cost-efficient manner. Method We initiated a quality improvement project involving the review of all patients with laboratory orders for PIFA testing between March 2017 to March 2018, explicitly assessing for documented 4T scores before the ordering of PIFA. Three of the investigators also calculated 4T scores for these patients at the time of laboratory testing and noted the results of the serotonin release assay (SRA), if ordered. We further collected data on any alternative anti-coagulation used in such patients for a cost-efficacy analysis later. Results A total of 170 PIFA tests were ordered during the period of investigation. Only five (0.02%) of these patients had a documented 4T score at the time of testing. One hundred thirteen patients (66.4%) had a low 4T score per investigator-calculation. Forty-seven patients (27.6%) were noted to have intermediate 4T scores. Lastly, ten patients (0.05%) were observed to have high 4T scores. A total of 32 SRAs were ordered; five of which were positive (four with an intermediate 4T score and one with high 4T score). PIFA was false-negative in two confirmed cases of positive SRA and false-positive in 13 instances of negative SRA. Thus, in this study, the sensitivity of PIFA was noted to be 60%, and specificity was observed to be 50%. Nineteen patients also received alternative parenteral anti-coagulation (fondaparinux or argatroban); seven of these were with low, eight with intermediate, and four with high 4T scores. Conclusion The study highlights the need for improving 4T score usage rates in our hospital as well as a need for switching to an alternative HIT screening test to promote patient safety and cost efficacy. Hence, we have begun the integration of 4T score with laboratory testing into the electronic medical record, alongside a shift in our HIT screening test from PIFA to the recently FDA-approved automated latex immunoturbidimetric assay. We will be continuing analysis of patients with suspected HIT for another six months to assess the effects of the above interventions. Figure. Figure. Disclosures No relevant conflicts of interest to declare.

314 Background: HIT diagnosis combines 4T scoring & HIT antibodies (HIT-Ab) testing, with confirmatory serotonin release assay (SRA). Latex immunoturbidometric assay (LIA) shows promise in quick & accurate HIT diagnosis, compared to particle immunofiltration assay (PIFA). We designed a HIT workflow & replaced PIFA with LIA at our hospital, to improve 4T usage rates & HIT diagnosis accuracy in a cost-efficient manner. Methods: In phase I, patients (pts) charts with HIT-Ab (PIFA) ordered between Mar2017-Mar2018 were retrospectively reviewed. Three investigators independently calculated 4T & reviewed PIFA/SRA results, with any alternative anticoagulation (AC) used. In phase II, a new workflow on electronic health record incorporating 4T algorithm with HIT-Ab test order was implemented. Our lab replaced PIFA with LIA. In phase II, charts for pts with LIA results from Jan-Mar 2019 were reviewed. Results: In phase I, 170 pts had PIFA results & 5 such pts (0.02%) had 4T score documented in chart. Per investigators, 113 (66.4%) pts had 4T scores. PIFA showed 60% sensitivity & 50% specificity compared to SRA. 19 pts received AC (4 pts had low 4T with negative PIFA). In phase II, 40 pts with LIA tested, 4T scoring by ordering physicians improved to 100%. Per investigators, 42.5% pts had low 4T scores. Clinicians documented high 4T in 11 pts; investigators confirmed high 4T in 2 pts. AC was used in 5 pts (4 with intermediate-high 4T per investigators) Conclusions: Our study showed that incorporation of 4T scoring in HIT algorithm significantly reduced unnecessary ordering of HIT-Ab, with 100% compliance in 4T reporting. Use of AC was consistent with the level of probability by 4T. Further clinician education can help in reduction of up scoring of 4T noted in our results. [Table: see text]