The Appropriateness of Heparin Antibody Testing. A Single Institution Retrospective Analysis

Background: Heparin-induced thrombocytopenia (HIT) is a drug-induced, immune-mediated prothrombotic disorder associated with thrombocytopenia and venous and/or arterial thrombosis.Up to 5% of patients exposed to heparin for at least one week develop HIT, and approximately 50% of them will have thrombosis. Diagnosis of HIT is suspected from the clinical picture based on the ''4 T's'' (Thrombocytopenia, Timing, Thrombosis, no other cause of platelet fall) or the HIT Expert Probability (HEP) scoring system. However, often these “4 T’s” are ignored and testing is inappropriately ordered in low risk patients. This could lead to possible morbidity and increase length of hospital stay. We opted to look back at the appropriateness of testing done within our academic center.

Methods/ Design:

All hospitalized patients with thrombocytopenia who underwent HIT antibody testing (HIT ELISA) during February 2013 were screened using our internal electronic medical record.

Patients were subdivided to low, intermediate or high pretest probability group according to the 4Ts scoring system.

Appropriateness of testing was determined according ASH 2013 Clinical Practice Guideline on the Evaluation and Management of Adults with Suspected Heparin-Induced Thrombocytopenia (HIT). HIT Ab test is recommended to be tested when there is intermittent to high probability of HIT (4T’s score above or equal to 4).

The percentage of appropriate/inappropriate testing was calculated.

The results were then subdivided by ordering physician group.

Results:

120 HIT ab tests were performed during February 2013 in our institution.  Only 13  patients tested had a positive HIT Ab. Internal medicine ordered the majority of these tests. Of the 120 patients tested, 7 patients had high risk and another 50 had intermediate risk as per 4T’s scoring.  61 patients were low risk and should not have been tested. (Table 1)

Table 1. HIT antibody test ordered per Service and probability of HIT.

Service ordering test	Low probability of HIT	Intermediate/high probability of HIT	TOTAL
Internal Medicine	28	28	56
Cardiothoracic Surgery	13	11	24
Hematology Oncology	7	5	12
Cardiology	3	1	4
Surgery	1	4	5
Emergency medicine	0	1	1
Infectious disease	4	0	4
Pulmonary	0	1	1
Critical care	1	6	7
Nephrology	1	2	3
Ob Gyn	1	0	1
Family Medicine	2	0	2
TOTAL	61	59	120

Conclusions:

HIT testing has been overused within our institution. Low platelets, without other signs or symptoms of typical HIT were used as a trigger for testing the antibody. This has potential to cause harm due to increased bleeding risk, increased length of hospital stay, and the potential to utilize extended anticoagulation when not necessary. Better education on the appropriateness of the test can limit the potential harm of its use.

Disclosures: No relevant conflicts of interest to declare.

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