Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin‐induced thrombocytopenia in two clinical settings

Abstract

Summary. Background: Heparin-induced thrombocytopenia (HIT) is a prothrombotic adverse drug reaction caused by heparin. As thrombocytopenia is common in hospitalized patients receiving heparin, it would be useful to have a clinical scoring system that could differentiate patients with HIT from those with other reasons for thrombocytopenia. Aim: To compare prospectively the diagnostic utility of a clinical score for HIT in two different clinical settings. Methods: The pretest clinical scoring system, the Ô4 T'sÕ, was used to classify 100 consecutive patients referred for possible HIT in one hospital (Hamilton General Hospital, HGH) into high, intermediate, and low probability groups. This system was also used to classify likewise 236 patients by clinicians in Germany referring blood for diagnostic testing for HIT in Greifswald (GW). The clinical scores were correlated with the results of laboratory testing for HIT antibodies using the serologic criteria for HIT with high diagnostic specificity. Results: In both centers, patients with low scores were unlikely to test positive for HIT antibodies [HGH: 1/64 (1.6%), GW: 0/55 (0%)

The management of abnormal haemostasis in the ICU

“…It is an intensely prothrombotic disorder which can be fatal when there is a delay in diagnosis. The treating team and haematology colleagues must have a high index of suspicion to facilitate diagnosis and treatment [36]. The pathophysiology of HIT centres on the development of pathological antibodies to the combination of heparin and platelet factor 4 (PF4).…”

“…Venous thrombosis (deep vein or pulmonary embolism) is common but arterial thromboses with limb ischaemia, cerebral vascular accidents and myocardial infarctions are also well described. Patients can develop necrotising skin lesions and may have a history of anaphylactoid reactions to heparin [36]. The '4Ts' score has been shown to predict the probability of HIT.…”

Heparin-induced Thrombocytopenia in the ICU: An Overview

“…Patients with low pretest scores (< 4 points) are unlikely to be positive for HIT antibodies (0 to 1.6%), whereas patients with intermediate (4-5 points) and high (> 5 points) scores are more likely to test positive (21.4% to 100%) [32]. Th e evaluation of this scoring system showed a high negative predictive value in the general population and in ICU patients, with low scores being suitable for ruling out HIT in most clinical situations [32].…”

Systematic review of fondaparinux for heparin‐induced thrombocytopenia: When there are no randomized controlled trials

“…The 4Ts score is the most commonly used prediction rule to determine the clinical pretest probability of HIT 2. However, the range of laboratory tests for HIT antibodies is wide with a correspondingly wide variability in sensitivity and specificity.…”