Introduction: For patients admitted to hospital, the use of heparin and its analogs is very common. Heparin administration can result in heparin-induced thrombocytopenia (HIT). Development of HIT is independent of the dose of heparin administration. Presence of HIT is determined by platelet antibody assays and confirmed by serotonin release assay. However, hospitalized patients have many comorbidities and are on several medications, both of which may be responsible for thrombocytopenia. The 4T scoring system was developed in 2006 to determine the pretest probability of HIT. Scores of 0-3, 4-5, and 6-8 are considered to correspond to a low, intermediate, and high probability of HIT, respectively. The 4T score was validated by a meta-analysis published in 2012 which reported that the negative predictive value of a low 4T score is close to 100% (Blood 2012;120(20):4160-4167). Inappropriate testing for thrombocytopenia can lead to inadvertent use of the platelet factor 4 assays, halting heparin administration unnecessarily and the over-treatment of patients with alternative anticoagulants. The American Society of Hematology (ASH) highlighted this in its 2014 Choosing Wisely guidelines (Blood 2014;124(24):3524-3528). The Choosing Wisely recommendations include using the 4T scoring system to assess the pretest probability of HIT. ASH recommends against testing and treating patients who have low pretest probability of HIT. We wanted to assess the impact of ASH Choosing Wisely recommendations on the appropriateness of checking for HIT.

Methods: All the patients, admitted between January 2013 to March 2016, who had a HIT test done (CPT code 86022), were extracted from the hospital database. Of these patients, 140 were randomly selected before and after the publication of ASH Choosing Wisely guidelines. The immediately previous platelet count before ordering a HIT test was used to calculate the platelet nadir. The percentage in platelet count fall was determined by the difference between the immediately previous platelet count before ordering HIT test and the maximum platelet count documented on current admission. Timing of platelet count fall was determined as the number of days from HIT testing ordered to when patient received the first dose of heparin, or from the date of the immediately previous platelet count before ordering HIT test to the maximum platelet count, whichever is less. Patients were considered to have suspected thrombosis if an ultrasound doppler lower extremity or CT chest was ordered, but the results were not available at the time of ordering the HIT test. 4T scores were calculated for the first HIT test ordered to determine if the patients were a low-risk or intermediate- to high-risk for HIT. We did a chi-square test without Yate's correction to check if there has been a proportionate increase in HIT testing for patients with 4T score greater than 3, after the Choosing Wisely recommendations were published in 2014. Student's t-test was used to determine if there has been a decrease in the number of HIT tests ordered per patient after the release of Choosing Wisely guidelines. Patients who were not fit to be calculated for 4T score were excluded.

Results: A total of 280 patient charts were reviewed. 23 patients were excluded as they received recent heparin and had platelet count fall within less than 4 days. Of the 129 patients admitted in 2013-2014, 31 (24%) were considered high/intermediate risk 4T score category. Of the 128 patients admitted from January 2015 to March 2016, 26 (20.3%) were considered high/intermediate risk 4T score category. The chi-square test did not show any difference between the two groups (chi-score 0.515 with 1 degrees of freedom, P = 0.47). However, the Student's t-test showed that the number of HIT tests ordered per patient declined significantly after the release of the Choosing Wisely guidelines (t = 2.09, P = 0.038).

Conclusions: Physician adherence to 4T scoring system has not yet changed after the release of ASH Choosing Wisely guidelines. However, repeated testing for HIT has declined significantly after the guideline release. More efforts need to be taken to improve the quality of care in this population.


Baranwal:MacNeal Hospital: Employment.

Author notes


Asterisk with author names denotes non-ASH members.

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