Testing for Heparin Induced Thrombocytopenia: Comparison of Practice at an Academic Center with Choosing Wisely Guidelines
Bibliographic record
Abstract
Abstract Background: The American Society of Hematology Choosing Wisely Guidelines 2014 recommend against testing for treatment of Heparin Induced Thrombocytopenia (HIT) in individuals at low risk, defined by a 4T score ≤ 3. Diagnosis of HIT relies on a combination of clinical characteristics and laboratory testing. The 4T score is a pretest probability score that defines clinical characteristics of HIT with reported negative predictive value of 99.8%. A new scoring model, the HIT Expert Probability (HEP) score, was introduced in 2010 and postulated to reduce inter-observer variability. The primary objective of this study was to examine compliance with guidelines at our institution; a 456 bed university hospital. Secondary objectives were to compare the performance of the 4T and HEP score in regards to inter-observer variability and the predictive value of low risk scores. Methods: Local practice is initial testing with anti-PF4 antibody enzyme immunoassay (EIA), and subsequent reflex serotonin release assay (SRA) if the EIA is positive or indeterminate. Consecutive patients with requests for HIT testing were identified from laboratory records. With Research Ethics Board approval, retrospective chart review was conducted by 3 reviewers who independently applied 4T and HEP scores; discrepancies were resolved by consensus. Adverse events including thrombosis, skin necrosis, heparin infusion reactions, bleeding (classified as major by ISTH criteria) and mortality were recorded. Inter-observer variability was assessed using the intraclass correlation (ICC). Results: Between 2013 January 1 and 2015 Feb 21, 76 patients were referred for EIA testing. Excluded from this analysis were 7 patients with prior history of HIT or with testing requested from an outside institution. Of the remaining 69, median age was 67 years (range 24-90), 36 (56%) were male, 49 (71%) admitted with a medical diagnosis and 20 (29%) under a surgical service. Hematology service was consulted at some point during admission in 25 (36%). Pretest probability was documented in 16 (23%). A greater percentage of patients with documented pre-test probability had a hematology consult 11 (69%) than patients without 5 (31%). Also, 36 (86%) patients without a documented pre-test probability were considered low risk by the 4T score. Table 1.Scoring systemPre-test probabilityTotalN=69 (%)EIA positiveSRA positive*4TLow (≤3)42 (61)9 (13)1* (1)Intermediate (4-5)25 (36)10 (14)4 (6)High (6-8)2 (3)2 (3)1 (1)HEPLow (≤2)35 (51)7 (10)1* (1)Intermediate (2-5)20 (29)17 (25)1 (1)High (≥6)14 (20)7 (10)4 (6)*If SRA inconclusive, result confirmed with anti-PF4 IgG**Admitted with ischemic leg requiring catheter directed thrombolysis. Rapid onset thrombocytopenia within 24 hours of heparin exposure. Prior heparin exposure 150 days prior. Heparin stopped. No alternative anti-coagulation. No sequelae of HIT. The ICC for the pre-test probabilityscores was0.796(95% CI 0.714- 0.860) for 4T and 0.742 (95% CI- 0.645-0.821) for HEP score. By risk category, ICC for 4T score was 0.667 (95% CI 0.553 - 0.765) and HEP score was 0.702 (95% CI 0.553 - 0.765). HIT testing was performed in patients classified as low risk; 42 (61%) according to 4T and 35 (45%) according to HEP score. Among the 42 classified as low risk by 4T score, heparin was held in 26 (55) % pending results of testing and alternative anticoagulation commenced in 14 (33%) (fondaparinux 13, argatroban 1), at prophylactic dose in 12 and at therapeutic dose in 1 without a separate indication for anticoagulation. One low risk patient suffered major bleeding and 2 had thrombotic events. Overall, bleeding occurred in 10 (14%), major in 6 (9%), and thrombotic events occurred in 9 (13%). One patient presenting with septic shock, who developed thrombocytopenia with 4T score of 4, received argatroban and died on the same day from intracranial hemorrhage. All cause mortality during admission was 23 (33%). Conclusion: Compliance with Choosing Wisely Guidelines at our institution is low, and potentially associated with unnecessary financial expenditure and patient harm due to over-testing and over-treatment. We did not observe benefit of the more complex HEP score over the 4T score. Efforts are underway to increase awareness and align practice with recommendations. Disclosures James: Biogen Idec: Honoraria; Bayer: Honoraria, Research Funding; Octapharma: Honoraria, Research Funding; Baxter: Honoraria; CSL Behring: Honoraria, Research Funding.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.006 | 0.034 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".