Testing for Heparin Induced Thrombocytopenia in Hospitalized Patients: In Line with Evidence?

Background: Heparin-induced thrombocytopenia (HIT) is an immune complication of heparin therapy caused by antibodies to complexes of platelet factor 4 (PF4) and heparin. Both clinical probability and laboratory testing are needed for establishing a diagnosis of HIT. The 4Ts clinical scoring system, due to a very high negative predictive value when low, offers a robust means to exclude a diagnosis of HIT. However, these strategies are under-employed in clinical practice and limited evidence indicates a high prevalence of over-testing for HIT. Methods: This retrospective analysis was conducted to identify patients who underwent heparin/PF4 antibody testing over a period of 12 months. The testing was performed using an ELISA-based IgG anti-heparin/PF4 antibody assay and an optical density (OD) of 0.4 was used as a cut-off for a positive value. Electronic medical records were reviewed for 4T score documentation, anti-PF4 results, SRA testing and 4T scores were retrospectively calculated for all the patients. SAS v9.4 (Cary, NC) was used for statistical analysis. Results: A total of 105 patients who underwent anti-PF4 antibody testing were included for analysis. Majority of the patients in our cohort were admitted in an intensive care unit setting (75/105,71.4%). On chart review, only 17 patients (16.2%) were noted to have documentation of 4T score. Based on the retrospectively calculated 4T scores, 60 patients (57.1%) had low pre-test probability, 41 (39%) had intermediate pre-test probability and 4 (3.8%) patients were noted to have high pre-test probability. Anti-PF4/heparin antibodies were positive in 9 patients, of which 5 (55.5%) patients did not undergo concomitant SRA testing. Out of 9, 4 (44.4%) had weakly positive (0.4-1.0 OD units), 2 (21.1%) had strongly positive (1.0-2.0 OD units) and 2 (21.1%) patients had very strongly positive (>2 OD units) anti-PF4 antibody titers. Out of 105 patients, SRA was tested in 11 patients (10.5%) and was noted to be positive in 1 (0.95%). Overall, 2 patients were diagnosed and treated for HIT, out of which the diagnosis was not confirmed with SRA in 1 patient (due to high pre-test probability and very strong anti-PF4 titers). In the remaining patients, sepsis (48, 46.6%) and drug-induced thrombocytopenia (29, 28.2%) emerged as the most common possible causes of thrombocytopenia. Conclusion: Among hospitalized patients, over-testing for HIT is common. Practices to promote 4T score documentation and evidence-based anti-PF4 testing may help prevent unnecessary costs associated with serological testing and costly alternate anticoagulants. To improve overall outcomes, clinicians should also attempt to identify and treat other more likely causes of thrombocytopenia, especially in patients with low pre-test probability for HIT. Disclosures No relevant conflicts of interest to declare.

Use of an argatroban systemic infusion and purge solution in a patient with a percutaneous ventricular assist device with suspected heparin-induced thrombocytopenia

Disclaimer In an effort to expedite the publication of articles , AJHP is posting manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time. Purpose Thrombocytopenia can occur when using an Impella percutaneous ventricular assist device (pVAD), and heparin-induced thrombocytopenia (HIT) is often suspected. Data on heparin- and anticoagulant-free purge solutions in these devices are limited. Previous case reports have described argatroban-based purge solutions, both with and without systemic argatroban, at varying concentrations in patients with known or suspected HIT. Summary A 33-year-old male was transferred to our institution and emergently initiated on life support with venoarterial extracorporeal membrane oxygenation (ECMO), an Impella pVAD, and continuous venovenous hemofiltration to receive an urgent aortic valve replacement. Over the next several days, the patient’s platelet count declined with a nadir of 17 × 10 3/µL on hospital day 13. The patient’s 4T score for probability of HIT was calculated as 4. All heparin products were discontinued on hospital day 15, and the patient was initiated on systemic infusion with argatroban 1,000 µg/mL at a rate of 0.2 µg/kg/min with a purge solution of argatroban 0.05 mg/mL. The systemic infusion remained at a rate of 0.2 µg/kg/min, and the total argatroban dose was, on average, less than 0.25 µg/kg/min. On hospital day 21, the patient was transferred to another institution. Conclusion Systemic infusion and a purge solution with argatroban were used in a patient with an Impella pVAD with multisystem organ dysfunction and suspected HIT. The patient achieved therapeutic activated partial thromboplastin times without adjustment of the systemic argatroban infusion and did not experience bleeding or thrombosis. Further studies concerning the safety and effectiveness of argatroban-based purge solutions in patients with pVADs are needed.

High Levels IPF as Possible Predictor Heparin-Induced Thrombocytopenia

Background: Heparin-Induced Thrombocytopenia (HIT) represents a serious complication of heparin treatment. IgG antibodies binding Platelet Factor 4 (PF4) and heparin trigger the clinical manifestations of HIT. A 4T score is used to stratify the selection of patients suitable for examination. However, the selection of suitable patients remains at the discretion of the clinician, who is confronted with determining the cause of thrombocytopenia. The inclusion of the evaluation of the Immature platelet fraction result seems to be a suitable complement to the stratification of patients because we do not climb elevated IPF values when consuming platelets due to their immunization. Materials and Methods: In a group of 432 thrombocytopenic samples IPF was detected and analyzed in 45 patients with suspected HIT, a 4T score was determined; IPF and HIT functional tests were examined. IPF was determined by oxazine fluorescent dyeing structures of nucleic acid-containing platelets and fluorescence detection on a Sysmex XN 1000 analyser. To determine HIT, impedance aggregometry using the Multiplate® analyser (MEA) as heparin-induced aggregation techniques. The MEA method uses sensitization of donor platelets with patient plasma in the presence of heparin at a concentration of 0.5IU/mL. Results: From the results of the test, it is evident that 10 patients from our group of 45 examined showed positivity of HIT, which is a significant number due to the proven occurrence of HIT in patients treated with LMWH and showing thrombocytopenia. If we evaluate these 10 patients in terms of IPF value, it is evident that 6 of them have an increased value of IPF >10%, which is a 33% positive predictive value and 4 have IPF >30%, when the positive predictive value is even 100%. Conclusions: Diagnosis of HIT remains a complicated clinical laboratory issue. However, new diagnostic options provide considerable potential for solving this problem. The implementation of IPF assays helps us in the diagnosis of HIT on two levels. On the one hand, it provides us with information on platelet consumption in hospitalized patients and thus draws our attention to HIT as one of the options for congestive thrombocytopenia, unless, of course, disseminated intravascular coagulation or thrombotic microangiopathy. Secondly, its implementation will increase the predictive value of the 4T score in patients at medium risk, which is, however, the vast majority indicated for HIT examination.

A Comparison of Scoring Systems for Predicting HIT in CABG Patients

Heparin induced thrombocytopenia is seen in patients with exposure to unfractionated heparin or low molecular weight heparin products. Surgical patients are at the highest risk for heparin induced thrombocytopenia (HIT) and patients undergoing coronary artery bypass graft (CABG) surgery have the second highest risk for developing heparin antibodies leading to HIT. Eight percent of heparin treated patients develop antibodies and 1-5% develop HIT; of these, 30-50% develop thrombosis along with the thrombocytopenia with a 20-30% morbidity and mortality rate. There are three different scoring systems typically used to determine the probability of HIT. These include the 4T score (most commonly used), HIT Expert Probability (HEP) score, and the Lillo-Le Louet (LLL) model scoring system (used exclusively for post-CABG patients). To date there have been limited studies done to compare the various scoring systems specifically in post CABG patients. The purpose of this study was to determine which scoring system was best at predicting the probability of HIT in a CABG patient. This is a single institution retrospective chart review of all patients between 2017-2019 who underwent CABG surgery. A total of 165 patients were studied and the patients who had HIT workup done were selected for further evaluation. Patient charts were reviewed to document initial platelet counts and post-CABG surgery platelet counts. Platelet counts were followed and documented for up to post-op day #15, if available. Review also included identification of new cases of arterial or venous thrombosis. For each patient that had HIT work-up, the HIT probability score was calculated by three different methods (4T score, HEP score, and LLL score). Sensitivity and specificity of the scoring systems was calculated. ANOVA test was used to determine if there was a difference between the three scoring systems and paired T-test was used to assess between the scoring systems. A total of 37 patients were studied and paired-T tests were used to compare between the scoring systems. There were a total of 6 patients with confirmed HIT based on a positive serotonin release assay (SRA) and 31 patients who had a negative work-up for HIT. The PPV of 4T, HEP, LLL was 0.545, 0.545, 0.667 respectively. Specificity was highest for LLL model: 0.912 and 0.861 for both HEP and 4T. ANOVA test determined in patients with a definitive HIT diagnosis that there was no difference among the 3 tests (p value=0.47792); however there was a difference between the scoring systems when the patients tested negative for HIT (p value= 0.00001). Furthermore, when individually comparing LLL to either 4T or HEP there was a significant difference in both true HIT and non-HIT patients p-value <0.03. These findings suggest that LLL is a better predictor of HIT in patients with CABG and it is especially superior in ruling out HIT in comparison to 4T and HEP. This further goes to support using LLL over 4T score in patients with CABG to help improve predictability of HIT. LLL is a simple calculation similar to 4T score and hence we should utilize it more often in our CABG patients. Disclosures No relevant conflicts of interest to declare.

Heparin Induced Thrombocytopenia in Patients with COVID-19

Background The Coronavirus disease-2019 (COVID-19) is a global pandemic caused by novel coronavirus SARS-CoV-2. Acute respiratory and renal failure as well as systemic coagulopathy are critical aspects of the morbidity and mortality in patients with COVID-19. Heparin Induced Thrombocytopenia (HIT) occurs when IgG antibodies form against platelet factor 4-Heparin complex, resulting in platelet activation and removal, leading to a prothrombotic state. HIT is suspected when there is a platelet count decrease of more than 50% after exposure to heparin, along with hypercoagulability. Clinical Scoring systems like 4T Score (Thrombocytopenia, Timing, Thrombosis, no other cause of Thrombocytopenia) have been developed to assess the pretest probability of HIT. The use of unfractionated heparin, post-orthopedic and post-cardiac surgery state, female gender, and old age are recognized as risk factors for HIT. There is a nine-fold increased risk of developing HIT in patients requiring hemodialysis. ICU patients and patients with VTE without thrombocytopenia are considered to have low pre-test probability for HIT. Studies have shown that only 6% who are investigated serologically for HIT actually have the diagnosis. We conducted this study to assess the incidence and risk factors for HIT in COVID-19 positive patients and its impact on mortality. Methods A retrospective analysis was performed on all patients who were COVID-19 positive and hospitalized between March 1, 2020 and June 26, 2020 at our institution. Patients with intermediate or high suspicion for HIT, based on 4T score of 4 or higher, underwent IgG-specific platelet factor 4(PF4)-dependent enzyme immune assay (EIA). Washed platelet assays such as serotonin release assay (SRA) and heparin-induced platelet aggregation (HIPA) were used as confirmatory tests in cases with intermediate or low optical density (OD) with EIA. The incidence of HIT, its impact on mortality, and positivity of IgG-specific PF4-EIA in COVID-19 patients were studied, and statistical analysis was done with X2 testing. Subgroup analysis was performed based on demographic factors and risk factors for HIT, including exposure to heparin or low molecular weight heparin (LMWH), history of or cancer, recent orthopedic or cardiac surgery, exposure to renal replacement therapy (RRT), and severity of disease (D-dimer >6 ULN, Acute Kidney Injury, ICU admission, and mechanical ventilation requirement). These factors were analyzed by Fisher's exact test to determine their impact on mortality. The hospital course for HIT antibody-positive patients was further analyzed to study the impact of COVID-19 related therapy, such as Remdesivir, Tocilizumab, Hydroxychloroquine, Steroids, and anticoagulation after diagnosis of HIT. Results WEight out of 1265 hospitalized COVID-19 positive patients tested positive for IgG-specific platelet factor 4(PF4)-dependent enzyme immune assay (EIA+). Incidence of EIA+ in COVID-19 patients was 0.6%, which is significantly higher than in the general population 0.2% (p<.0001, 95% CI 0.25-1.20%). The incidence of thromboembolic events in EIA+ patients was 87.5%, significantly higher than the rate of 10.90% in all COVID-19 patients (p<.0001, CI 41.96- 86.98%). The mortality rate in EIA+ patients was 50%, significantly greater than the mortality rate of 12% in all hospitalized COVID-19 patients (p=.0011, CI 9.46-66.53). Serological confirmation of HIT diagnosis was 37.5% (2 had OD>1, 1 was SRA positive) which is significantly higher than confirmation of HIT in nonCOVID-19 patients 6% (p<.0001, 95% CI 29.57-85.32%). All 3 confirmed HIT patients (100%) had severe disease (3/3 required ICU admission, 2/3 required mechanical ventilation, the one not requiring mechanical ventilation required RRT). Conclusion Our study indicates incidence of HIT is higher in the COVID-19 population. The incidence of positive EIA for patients with intermediate to high 4T scores is also higher in COVID-19 positive patients. This can be attributed to the cytokine storm and severe sepsis seen in critically ill COVID-19 patients. Our study also suggests that development of HIT can contribute to increased risk for thromboembolic events as well as mortality of COVID-19 patients, however, our study is limited due to small sample size. Therefore, prospective studies are needed to analyze the impact of HIT on morbidity, mortality and long-term outcomes in COVID-19 patients. Table Disclosures No relevant conflicts of interest to declare.

Daumenmikrothrombose/Daumennekrose eines Patienten mit heparininduzierter Thrombozytopenie

ZusammenfassungWir berichten über einen 81-jährigen Patienten, der unter der Therapie mit unfraktioniertem Heparin (UFH) in prophylaktischer Dosierung eine heparininduzierte Thrombozytopenie mit Mikrothromben und beginnender Nekrose entwickelt hat. Die Prophylaxe wurde mit UFH durchgeführt. An Tag 10 kam es zu einem Thrombozytenabfall um > 50%. Eine Daumennekrose weckte den Verdacht auf eine heparininduzierte Thrombozytopenie (HIT). Der 4T-Score zeigte eine hohe Wahrscheinlichkeit für eine HIT auf (7 Punkte). Da der Schnelltest positiv ausfiel, wurde eine therapeutische Antikoagulation mit Argatroban (2 µg/kg/min) bereits vor vollständiger labortechnischer Abklärung begonnen. Sowohl die Thrombozytenzahl als auch der Daumen erholten sich innerhalb von 5 Tagen nach der Umstellung auf Argatroban. Unser Fallbeispiel zeigt, dass bei dem Verdacht auf HIT eine sofortige Umstellung auf alternative Antikoagulation in therapeutischer Dosis zur Reversion beginnender Nekrosen führen kann.

CME: Heparin-induzierte Thrombozytopenie

Zusammenfassung. Die Heparin-induzierte Thrombozytopenie (HIT) ist eine gefährliche, potenziell tödliche, immunologisch vermittelte Nebenwirkung von Heparin. Typischerweise fünf bis zehn Tage nach Heparin-Exposition kommt es zu einem Abfall der Thrombozytenzahl mit einem Mittelwert von 60 x 109/l. Aufgrund einer Aktivierung der Thrombozyten durch HIT-Antikörper können venöse oder seltener arterielle Thrombosen auftreten. Die Diagnostik der HIT beinhaltet die Berechnung der Wahrscheinlichkeit einer HIT mittels dem 4T-Score, sowie den laborchemischen Nachweis von HIT-Antikörpern. Die Therapie der HIT stellt das sofortige Absetzen der Heparintherapie sowie den Beginn mit einer alternativen therapeutischen Antikoagulation dar.

Is Heparin Induced Thrombocytopenia Expert Probability (HEP) Scoring System Superior to 4T'S Scoring in the Diagnosis of Heparin Induced Thrombocytopenia? a Prospective Observational Study from a Tertiary Care Cardiac Centre in India

Heparin-induced thrombocytopenia (HIT) is a drug-induced thrombocytopenia that results in thrombotic complications rather than bleeding.In many countries like India, the availability of functional assay for diagnosing HIT is unavailable. But with the utility of scoring systems the probability of HIT can be assessed and can guide the intervention required. Presently there are two well characterised and easily calculated scoring systems, which are the commonly used 4T scoring system and newly designed HEP score, to overcome some of the limitations of 4T`s scoring system. The 4Ts score has a negative predictive value (NPV) approaching 100%, but is limited by modest positive predictive value (PPV) and significant inter-observer variability.In this study we are comparing the two scoring systems and their relevance in the Indian scenario in patients undergoing cardiac intervention, receiving heparin. METHODS: - We recruited 100 patients with suspected HIT, for whom antibody testing was orderedat our centre (Narayana Health City, Bangalore, India) between November 2017 and May 2018. - Data were collected at baseline diagnosis in the form of clinical and laboratory data. 4T`s score and the HEP score was calculated based on the above details before the availability of antibody test. - HIT antibody testing was done using ID-PaGIA Heparin/pF4 Antibody Test Kit with control. In this 10 millilitre of serum is pippeted into the upper chamber of the appropriate microtube. Incubate the ID card at room temperature for 5mins at room temperature (18-25oc). Later centrifuge the ID-card for 10mins in the ID-centrifuge then read and records the results. - Patients were followed up daily till the discharge and complete blood picture including WBC count, development of any adverse effects including renal failure, sepsis, intra-arterial device insertion, bleeding was noted. - Area under the curve (AUC) for the receiver operating curve (ROC) of HEP and 4T scores was calculated and p value was obtained based on these curves. RESULTS: - 37 patients were HIT antibody positive out of 100 patients with suspected HIT from a patient population of 26430, who received heparin. The overall incidence of HIT in our institute is 0.14% (37/26430). - Out of the 100 suspected patients 37 were proven to have HIT by using ID-PaGIA Heparin/PF4 rapid gel agglutination assay. In this series, 91% patients had undergone cardiothoracic surgery forming the majority. Two-thirds of the study population was in the age group (41-70years). Males (61%) are more in the study than females (39%).The percentage of HIT positivity was more in females (43.5) than males (32.7%). - In 87 patients who received UFH, who presented with thrombocytopenia during their perioperative period, 30 were proven to have HIT (34.4%).We also observed during that the total leucocyte count at the nadir of platelet was higher in thr HIT positive group. However, it was not statistically significant (p-0.283) - Out of 100 patients with suspected HIT 49% expired. Of the 37 cases proven to have HIT 20 patients expired (54%). There was no statistically significant association between the occurrence of HIT and mortality ( p-value =0.438). - In this study, the areas under the curve for predicting HIT by 4T score was more than HEP score (0.754 and 0.66) with P value-0.093. As the HEP score was not superior to 4T score we have evaluated 2 subgroup analysis. - Among 36 subjects with the intra-arterial device (included in HEP score), 12 were positive for HIT (33.3%). Area under the Curve for the 4T score (0.698) was higher than that for HEP score (0.599) although the difference was not statistically significant(p-0.3906) - In this study, the incidence of renal replacement therapy (not included in HEP score)was 43%. In this patient population, 46% (n=20) are HIT positive. Among subjects on RRT, 4T score (814) had higher Area under the curve compared to HEP score (0.607) in the diagnosis of HIT positivity and the difference was statistically significant (p value 0.035). CONCLUSION The newly diagnosed HEP scoring system, which includes additional causes of thrombocytopenia was not superior to the 4T's score in this study. The inclusion of intra-arterial device in the HEP score did not make a difference in prediction of HIT. Conversely the 4T score was superior to HEP score in the evaluation of the subset of patients on renal replacement therapy, a significant cause of thrombocytopenia, which was not included in the scoring system. Disclosures No relevant conflicts of interest to declare.

Diagnostic Performance of Heparin-Platelet Factor 4 Antibodies in the Identification of Heparin-Induced Thrombocytopenia in Cancer Population

Introduction: Cancer patients appear to have a higher risk of heparin induced thrombocytopenia (HIT) related complications than non-cancer patients; yet data on the performance of conventional diagnostic tools for HIT in cancer is limited. Our aim was to determine among cancer patients with a 4T score ≥ 4, the performance of the conventional cut-off for HIT antibody testing (IgG anti PF4) to discriminate between serotonin release assay (SRA) positive and negative cases. Methods: Retrospective and prospective analysis of cases (2002-2019) was performed of the electronic medical records of adult cancer patients at MD Anderson Cancer Center with suspected HIT. Cases were included in the analysis if the 4T score was ≥ 4 and investigated with IgG anti-PF4 optical density (HIT OD) and SRA. Logistic regression model and the receiver operating characteristic curves were conducted to identify the sensitivity and specificity of different cut-off points for the HIT OD to discriminate HIT cases based on the SRA status. Results: Among 50 cases, 18 were SRA positive. Median HIT OD was 1.03. At a cut-off point of 0.4, the HIT OD performed with a sensitivity of 0.89 and a specificity of 0.50 to discriminate the cases of SRA positive HIT. When the cut-off HIT OD was 1.0, the sensitivity was 0.78 with a specificity of 0.66. Conclusions: Our findings suggest that in cancer patients the performance of IgG anti-PF4 is similar to that of non-cancer patients for the identification of HIT cases. Disclosures Oo: Janssen and Janssen: Other: Research: site co-investigator ; Medical Education Speakers Network: Honoraria.