Venous limb gangrene and fatal hemorrhage: adverse consequences of HIT "overdiagnosis" in a patient with antiphospholipid syndrome

Prevalence of Heparin-Induced Thrombocytopenia in Hospitalized Patients with Antiphospholipid Syndrome or Lupus with Antiphospholipid Antibodies

OBJECTIVE

This study aims to investigate the prevalence of heparin-induced thrombocytopenia among hospitalized patients with antiphospholipid syndrome or systemic lupus erythematosus with antiphospholipid antibodies.

METHODS

A retrospective cohort study was performed on patients hospitalized at a tertiary care medical center who met criteria for antiphospholipid syndrome or lupus with antiphospholipid antibodies and were evaluated for heparin-induced thrombocytopenia with anti-platelet factor 4 or serotonin release assay. Pretest probabilities of heparin-induced thrombocytopenia were estimated using a 4T score. Proportions of patients with positive anti-platelet factor 4 and serotonin release assay tests were calculated, and the number of patients meeting clinical criteria for heparin-induced thrombocytopenia was determined.

RESULTS

Of 33 patients identified in screening, 23 met inclusion criteria. Pretest probability for heparin-induced thrombocytopenia based on 4T scores was intermediate in 9 (39%) and high in no patients. Only one patient (4%) tested positive for anti-platelet factor 4. Serotonin release assay was tested in four patients (17%) and was negative in all cases.

CONCLUSION

Among 23 hospitalized patients with antiphospholipid syndrome or lupus with antiphospholipid antibodies who were tested, none were diagnosed with heparin-induced thrombocytopenia. Most patients had low pretest probability for heparin-induced thrombocytopenia based on 4T scores but were still tested for anti-platelet factor 4. Our study suggests that heparin-induced thrombocytopenia is rare among hospitalized patients with antiphospholipid syndrome or lupus with antiphospholipid antibodies.

Clinical features, risk factors, and outcomes of diffuse alveolar hemorrhage in antiphospholipid syndrome: A mixed-method approach combining a multicenter cohort with a systematic literature review

BACKGROUND

Antiphospholipid syndrome (APS) is a systemic autoimmune disease clinically associated with thrombotic and obstetric events. Additional manifestations have been associated with APS, like diffuse alveolar hemorrhage (DAH). We aimed to summarize all the evidence available to describe the presenting clinical features, their prognostic factors, and short- and long-term outcomes.

METHODS

We performed a mixed-method approach combining a multicenter cohort with a systematic literature review (SLR) of patients with incident APS-associated DAH. We described their clinical features, treatments, prognostic factors, and outcomes (relapse, mortality, and requirement of mechanical ventilation [MV]). Kaplan-Meier methods were used to estimate relapse and mortality rates, and Cox and logistic regression models were used to assess the factors associated as appropriate.

RESULTS

We included 219 patients with incident APS-associated DAH (61 from Mayo Clinic and 158 from SLR). The median age was 39.5 years, 51% were female, 29% had systemic lupus erythematosus, and 34% presented with catastrophic APS (CAPS). 74% of patients had a history of thrombotic events, and 26% of women had a history of pregnancy morbidity; half of the patients had a history of thrombocytopenia, and a third had valvulopathy. Before DAH, 55% of the patients were anticoagulated. At DAH onset, 65% of patients presented hemoptysis. The relapse rate was 47% at six months and 52% at one year. Triple positivity (HR 4.22, 95% CI 1.14-15.59) was associated with relapse at six months. The estimated mortality at one and five years was 30.3% and 45.8%. Factors associated with mortality were severe thrombocytopenia (< 50 K/μL) (HR 3.10, 95% CI 1.39-6.92), valve vegetations (HR 3.22, 95% CI 1.14-9.07), CAPS (HR 3.80, 95% CI 1.84-7.87), and requirement of MV (HR 2.22, 95% CI 1.03-4.80). Forty-two percent of patients required MV on the incident DAH episode. Patients presenting with severe thrombocytopenia (OR 6.42, 95% CI 1.77-23.30) or CAPS (OR 4.30, 95% CI 1.65-11.16) were more likely to require MV.

CONCLUSION

APS-associated DAH is associated with high morbidity and mortality, particularly when presenting with triple positivity, thrombocytopenia, valvular involvement, and CAPS.

Quality improvement approaches to heparin-induced thrombocytopenia: a scoping review

Background

Heparin-induced thrombocytopenia (HIT) is a relatively uncommon condition characterized by 2 exceedingly common phenomena in hospitalized patients: thrombocytopenia and heparin exposure. Consequently, HIT is frequently overdiagnosed and inappropriately treated. These issues are the focus of many quality improvement (QI) initiatives.

Objectives

In this scoping review, we identified and characterized all published QI studies on improving the diagnosis and management of HIT.

Methods

We conducted a systematic literature search through April 2022 for studies reporting on QI interventions regarding the diagnosis, treatment, and/or prevention of HIT.

Results

Thirty studies were included in the final review. Studies were separated into 5 groups based on the focus of the interventions: increasing HIT recognition, reducing HIT incidence, reducing HIT overdiagnosis, promoting safer HIT management, and creating HIT task forces. Nine studies focused on the implementation of 4Ts score calculator into electronic medical record orders for HIT testing, while only 1 evaluated the impact of reducing unfractionated heparin use in favor of low-molecular-weight heparin. Six studies focused on the implementation of direct thrombin inhibitor management protocols, while none evaluated the use of alternative anticoagulants in HIT management.

Conclusion

The bulk of published HIT QI research focused on reducing overdiagnosis and promoting safer direct thrombin inhibitor therapy, while minimal attention has been devoted to HIT prevention and the use of evidence-based alternative HIT therapies.

Monitoring and Dosing of Argatroban in a Patient With Antiphospholipid Syndrome

Background: This case reports outlines argatroban dosing and necessary dose adjustments in a 56 year-old male with a past medical history of antiphospholipid syndrome and heparin-induced thrombocytopenia. Method: Argatroban was initiated as a fixed dose of 0.5 µg/kg/min with all initial aPTTs above goal. Argatroban was held for a procedure and re-initiated at 0.25 µg/kg/min. The dose was increased or decreased by 25% from the current rate based on supratherapeutic and subtherapeutic aPTTs, respectively. Results: The patient remained on argatroban for 6 total days, while achieving goal aPTT levels with no VTE or bleeding events. Conclusion: Our patient represents the first reported case of monitoring argatroban with aPTTs in an individual with APS.

Label-Free Detection and Characterization of Heparin-Induced Thrombocytopenia (HIT)-like Antibodies

Heparin-induced thrombocytopenia (HIT) antibodies (Abs) can mediate and activate blood cells, forming blood clots. To detect HIT Abs, immunological assays with high sensitivity (≥95%) and fast response are widely used, but only about 50% of these tests are accurate as non-HIT Abs also bind to the same antigens. We aim to develop biosensor-based electrical detection to better differentiate HIT-like from non-HIT-like Abs. As a proof of principle, we tested with two types of commercially available monoclonal Abs including KKO (inducing HIT) and RTO (noninducing HIT). Platelet factor 4/Heparin antigens were immobilized on gold electrodes, and binding of antibodies on the chips was detected based on the change in the charge transfer resistance (R _ct). Binding of KKO on sensors yielded a significantly lower charge transfer resistance than that of RTO. Bound antibodies and their binding characteristics on the sensors were confirmed and characterized by complementary techniques. Analysis of thermal kinetics showed that RTO bonds are more stable than those of KKO, whereas KKO exhibited a higher negative ζ potential than RTO. These different characteristics made it possible to electrically differentiate these two types of antibodies. Our study opens a new avenue for the development of sensors for better detection of pathogenic Abs in HIT patients.

Heparin-Induced Thrombocytopenia in COVID-19

COVID-19 (coronavirus disease-2019) infection is a highly prothrombotic state, resulting from a dysregulation of the coagulation cascade. Therefore, thromboprophylaxis is strongly recommended in these patients, with some experts even advocating for therapeutic dosing to prevent thromboembolic events. Heparin-induced thrombocytopenia (HIT) is a well-known complication of heparin therapy. In this article, we report a case of HIT in a patient with COVID-19. A 63-year-old male presented with 1 week of dry cough and diarrhea. He had a positive nasopharyngeal COVID-19 reverse-transcriptase–polymerase chain reaction. On admission, the platelet count and liver function tests were within normal limits. During his hospitalization, he developed a right femoral deep venous thrombosis and was started on therapeutic anticoagulation. Due to worsening respiratory failure, he was intubated and mechanically ventilated. Between days 11 and 12 of hospitalization, platelet count dropped from 304 000 to 96 000 cells/µL. He had a high pretest probability for HIT with a 4T score of 6 and a positive anti-PF4/heparin antibody. Heparin drip was discontinued and was switched to argatroban. The serotonin release assay eventually returned positive, which confirmed the diagnosis of HIT. We also discuss potential overdiagnosis of HIT in COVID-19 through 4 cases with false-positive HIT antibodies.

Clinical effectiveness of a Bayesian algorithm for the diagnosis and management of heparin-induced thrombocytopenia

Essentials We previously published a diagnostic algorithm for heparin-induced thrombocytopenia (HIT). In this study, we validated the algorithm in an independent large healthcare system. The accuracy was 98%, sensitivity 82% and specificity 99%. The algorithm has potential to improve accuracy and efficiency in the diagnosis of HIT.

SUMMARY

Background Heparin-induced thrombocytopenia (HIT) is a life-threatening drug reaction caused by antiplatelet factor 4/heparin (anti-PF4/H) antibodies. Commercial tests to detect these antibodies have suboptimal operating characteristics. We previously developed a diagnostic algorithm for HIT that incorporated 'four Ts' (4Ts) scoring and a stratified interpretation of an anti-PF4/H enzyme-linked immunosorbent assay (ELISA) and yielded a discriminant accuracy of 0.97 (95% confidence interval [CI], 0.93-1.00). Objectives The purpose of this study was to validate the algorithm in an independent patient population and quantitate effects that algorithm adherence could have on clinical care. Methods A retrospective cohort comprised patients who had undergone anti-PF4/H ELISA and serotonin release assay (SRA) testing in our healthcare system from 2010 to 2014. We determined the algorithm recommendation for each patient, compared recommendations with the clinical care received, and enumerated consequences of discrepancies. Operating characteristics were calculated for algorithm recommendations using SRA as the reference standard. Results Analysis was performed on 181 patients, 10 of whom were ruled in for HIT. The algorithm accurately stratified 98% of patients (95% CI, 95-99%), ruling out HIT in 158, ruling in HIT in 10 and recommending an SRA in 13 patients. Algorithm adherence would have obviated 165 SRAs and prevented 30 courses of unnecessary antithrombotic therapy for HIT. Diagnostic sensitivity was 0.82 (95% CI, 0.48-0.98), specificity 0.99 (95% CI, 0.97-1.00), PPV 0.90 (95% CI, 0.56-0.99) and NPV 0.99 (95% CI, 0.96-1.00). Conclusions An algorithm incorporating 4Ts scoring and a stratified interpretation of the anti-PF4/H ELISA has good operating characteristics and the potential to improve management of suspected HIT patients.

Inappropriate documentation of heparin allergy in the medical record because of misdiagnosis of heparin-induced thrombocytopenia: frequency and consequences

Essentials Misdiagnosis of heparin-induced thrombocytopenia (HIT) may be associated with adverse outcomes. We conducted a study of patients with a heparin allergy in the chart due to misdiagnosis of HIT. 42% of patients with a heparin allergy due to suspected HIT were clearly HIT-negative. 68% were unnecessarily treated with an alternative anticoagulant, 66% of whom had major bleeding.

SUMMARY

Background It is recommended that heparin be added to the allergy list of patients with heparin-induced thrombocytopenia (HIT). Misdiagnosis of HIT could lead to inappropriate documentation of a heparin allergy and adverse outcomes. Objectives To determine the frequency and consequences of inappropriate documentation of a heparin allergy because of misdiagnosis of HIT. Methods We conducted a cohort study of patients with an inappropriate heparin allergy listed in the electronic medical record (EMR) because of misdiagnosis of HIT. We searched the EMR for patients with a new heparin allergy. Patients were eligible if the reason for allergy listing was suspected acute HIT and laboratory testing for HIT was performed within 60 days. Subjects were defined as 'HIT-negative' if they had a 4Ts score of ≤ 3 or negative laboratory test results. Results Of 239 subjects with a new heparin allergy documented because of concern regarding HIT, 100 (42%) met the prespecified definition of HIT-negative. Sixty-eight (68%) HIT-negative subjects unnecessarily received an alternative parenteral anticoagulant for a median duration of 10.5 days. Among these 68 patients, 45 (66%) met criteria for major bleeding. Sixty-eight (68%) of the 100 HIT-negative subjects had an inappropriate allergy to heparin documented that persisted in the EMR for > 3 years beyond the index hospitalization. Conclusions Inappropriate listing of heparin as an allergy in the EMR because of misdiagnosis of HIT is common, is associated with substantial rates of unnecessary alternative anticoagulant use and major bleeding, and tends to persist beyond the index admission.

Over-testing for heparin induced thrombocytopenia in hospitalized patients

Heparin induced thrombocytopenia (HIT) is a pro-thrombotic and potentially fatal complication of heparin therapy. Its diagnosis rests on high clinical probability and the laboratory demonstration of anti-PF4/heparin antibodies. The high prevalence of thrombocytopenia in hospitalized patients and the high sensitivity but low specificity of immunoassays for HIT antibodies can lead to over-testing and over-diagnosis. We conducted a study to review HIT screening practices in a tertiary care setting. We reviewed 63 consecutive patients undergoing testing for anti-PF4/heparin antibodies over 3 months. Pre-test probability for HIT was calculated using the 4T score. Sixty three patients underwent testing for anti-PF4/heparin antibodies. Twenty one had been admitted for cardiovascular surgery, 5 for other surgery and 35 for non-surgical indications. Twenty nine patients (46 %) had low pre- test probability, twenty three (36.5 %) had intermediate probability, and eleven (17.4 %) had high pre-test probability of having HIT. Anti-PF4/heparin ELISA was positive in 8 of 63 patients. SRA was ordered for 16 patients and was positive in 5. Only five patients were diagnosed and treated for HIT. Over-testing for HIT is highly prevalent in a tertiary care setting. This increases cost and exposes patients to expensive anti-coagulation with its attendant risk of hemorrhage. The 4Ts score has been shown to have high sensitivity and may be used to rule out HIT in most situations, although its utility depends on subjective analysis. Consistently applying this in practice could minimize over-testing and facilitate safer, cost-effective care.

Phlegmasia Cerulea Dolens in the Upper Extremity

Phlegmasia cerulea dolens (PCD) is a rare form of venous gangrene that arises secondary to occlusion of venous outflow from a limb. Classically described in the lower extremity, it is rare in the upper extremity. We present a case report of upper extremity PCD and a systematic review with data analysis of 37 cases of PCD published in PubMed. Our analysis showed that concurrent lower extremity PCD was a statistically significant marker for worse outcomes in this patient population.

Clinical and laboratory characteristics associated with a high optical density anti-platelet factor 4 ELISA test

PURPOSE

Diagnosing heparin-induced thrombocytopenia, a potentially catastrophic immune-mediated disorder, continues to pose significant challenges for clinicians, as both clinical and laboratory tools lack specificity. There is mounting evidence supporting a positive correlation between definitive heparin-induced thrombocytopenia and optical density (OD) positivity from the widely available anti-platelet factor 4 enzyme-linked immunosorbent assays (PF4 ELISAs). However, the clinical features distinguishing these patients remain poorly understood.

PATIENTS AND METHODS

To better characterize this group, we conducted a case-controlled, retrospective chart review of patients from two large, urban academic institutions who underwent a PF4 ELISA at a central laboratory. Associations between OD and 18 clinical characteristics were calculated using the Fisher's exact test for categorical variables and Wilcoxon rank-sum test for continuous variables.

RESULTS

In total, 184 negative patients (OD <0.7), and 121 positive patients (OD >0.7), including 74 low-positive patients (0.7< OD <1.4) and 47 high-positive patients (OD >1.4) were identified. Several clinical variables were significantly different in the negative group compared with the positive group, including hospital day (P<0.001), previous admission within the past 3 months (P<0.001), and the presence of a new thrombus (P=0.003). However, many of these variables were not different between the negative and low-positive group, and were only distinct between the negative and high-positive group. When the low-positive and high-positive groups were compared, only the 4T score was significantly different (P=0.003).

CONCLUSION

These data indicate that those with OD >1.4 form a distinct clinical group and support the clinical utility of the 4T score.

Using HitAlert flow cytometry to detect heparin-induced thrombocytopenia antibodies in a tertiary care hospital

We aimed to assess the utility of HitAlert flow cytometry as a diagnostic functional heparin-induced thrombocytopenia (HIT) assay in a tertiary care hospital. The 4Ts score was used to assess pretest probability of HIT in 37 patients. Serum was analysed for HIT antibodies by the flow cytometry HitAlert assay. Results were compared with an antigenic assay, the particle gel immunoassay, PaGIA ID PF4/Hep Ab assay; and two functional assays, the Multiplate whole blood impedance aggregometry assay (WBIA), and the serotonin release assay (SRA). Flow cytometry was positive in 14 out of 37 patients, including zero out of eight, five out of 19 and nine out of 10 in the low, intermediate and high-risk groups by 4Ts score, respectively. Using the SRA as a 'gold standard', flow cytometry has a sensitivity of 81% and a specificity of 100% for the diagnosis of HIT. The other functional assay (WBIA) had similar sensitivity (81%) and specificity (90%) to flow cytometry. In contrast, the PaGIA maintained a high sensitivity of 100% but a specificity of only 20%. The improved specificity of flow cytometry over the antigenic assay was most marked in the 4T intermediate-risk group in which similar results were obtained between all three functional assays. We demonstrate that compared with an immunological assay (PaGIA), flow cytometry can improve the specificity of laboratory diagnosis of HIT without loss of sensitivity using SRA as a standard. Flow cytometry may have a role in the first-line laboratory diagnosis of HIT, especially when combined with an immunological assay such as PaGIA.

Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis

The 4Ts is a pretest clinical scoring system for heparin-induced thrombocytopenia (HIT). Although widely used in clinical practice, its predictive value for HIT in diverse settings and patient populations is unknown. We performed a systematic review and meta-analysis to estimate the predictive value of the 4Ts in patients with suspected HIT. We searched PubMed, Cochrane Database, and ISI Web of Science for studies that included patients with suspected HIT, who were evaluated by both the 4Ts and a reference standard against which the 4Ts could be compared. Quality of eligible studies was assessed by QUADAS-2 criteria. Thirteen studies, collectively involving 3068 patients, fulfilled eligibility criteria. A total of 1712 (55.8%) patients were classified by 4Ts score as having a low probability of HIT. The negative predictive value of a low probability 4Ts score was 0.998 (95% CI, 0.970-1.000) and remained high irrespective of the party responsible for scoring, the prevalence of HIT, or the composition of the study population. The positive predictive value of an intermediate and high probability 4Ts score was 0.14 (0.09-0.22) and 0.64 (0.40-0.82), respectively. A low probability 4Ts score appears to be a robust means of excluding HIT. Patients with intermediate and high probability scores require further evaluation.

HITlights: a career perspective on heparin-induced thrombocytopenia

Two decades of research into heparin-induced thrombocytopenia (HIT) permit a personal historical perspective on this fascinating syndrome. Previously, the frequency of HIT was unknown, although complicating thrombosis was believed to be rare and primarily arterial. The opportunity to apply a remarkable test for "HIT antibodies"--the (14) C-serotonin-release assay (SRA)--to serial plasma samples obtained during a clinical trial of heparin thromboprophylaxis, provided insights into the peculiar nature of HIT, such as, its prothrombotic nature--including its strong association with venous thrombosis (RR = 11.6 [95%CI, 6.4-20.8; P < 0.0001); its more frequent occurrence with unfractionated versus low-molecular-weight heparin; the "iceberg" model, which states that among the many patients who form anti-PF4/heparin antibodies during heparin therapy, only a minority whose antibodies evince strong platelet-activating properties develop HIT; and the characteristic HIT timeline, whereby serum/plasma antibodies are readily detectable at or prior to the HIT-associated platelet count fall. Applying the SRA also to patients encountered in clinical practice led to recognition of warfarin-induced venous limb gangrene (for which HIT is a major risk factor via its extreme hypercoagulability) and delayed-onset HIT (whereby thrombocytopenia begins or worsens following heparin discontinuation, due to the ability of HIT antibodies strongly to activate platelets even in the absence of heparin--so-called heparin-"independent" platelet activation). Recent concepts include the increasing recognition of HIT "overdiagnosis" (due to the low diagnostic specificity of the widely-applied PF4-dependent immunoassays), and the observation that HIT-associated consumptive coagulopathy is a risk factor for treatment failure with PTT-adjusted direct thrombin inhibitor therapy ("PTT confounding" secondary to HIT-associated coagulopathy).

HIT paradigms and paradoxes

The current major problem with HIT is its overdiagnosis. This concept follows from the HIT central paradigm: HIT is caused by a subset of antibodies against platelet factor 4 (PF4)/heparin complexes that have strong platelet-activating properties. Prospective studies show that only a minority of sera containing such antibodies exhibit platelet-activating properties. Ironically, the earliest tests for HIT--platelet activation assays--remain today the most diagnostically useful, particularly the washed platelet assays. But the wider application of PF4-dependent immunoassays, and their much greater sensitivity for the larger subset of non-platelet-activating (and non-HIT-inducing) antibodies, has resulted in HIT overdiagnosis in many centres. Studies of anti-PF4/heparin immunization in diverse clinical situations have provided insights into the factors that influence the HIT immune response. Besides the conundrum of anticoagulant-induced thrombosis (including its potentiation of coumarin-induced microthrombosis), HIT evinces numerous other paradoxes: (i) it is a platelet-activating disorder with venous thrombosis as its predominant clinical manifestation; (ii) 'delayed-onset' (or 'autoimmune') HIT can lead to dramatic worsening of HIT-associated thrombosis despite cessation of heparin; (iii) partial thromboplastin time (PTT) monitoring of direct thrombin inhibitor treatment - and confounding of PTT monitoring by HIT-associated consumptive coagulopathy - infers that the worst subset of HIT patients may fail this therapeutic approach; (iv) the highly sulfated pentasaccharide anticoagulant, fondaparinux, can (rarely) cause HIT yet appears to be an effective treatment for this disorder; and (v) the transience of the HIT immune response means that many patients with previous HIT can safely receive future heparin.