The 4Ts scoring system for heparin-induced thrombocytopenia in medical-surgical intensive care unit patients.
ABSTRACT Heparin-induced thrombocytopenia (HIT) is commonly considered but rarely confirmed in critically ill patients. The 4Ts score (Thrombocytopenia, Timing of thrombocytopenia, Thrombosis, and oTher reason) might identify individual patients at risk of having this disorder.
The aim of the study was to evaluate the value of the 4Ts HIT score in comparison with the serotonin-release assay (SRA) in critically ill patients.
This study describes the combined results of 3 prospective studies enrolling critically ill patients who were investigated for HIT if platelets fell to less than 50 x 10(9)/L or if platelet counts decreased to less than 50% of the value upon intensive care unit admission. We confirmed HIT by a positive platelet SRA. We assigned a 4Ts score blinded to SRA results to all 50 patients investigated for HIT; those with positive SRA results were scored in duplicate.
Of 528 patients, 50 (9.5%) were investigated for HIT; 39 (78%) of 50 (64%-88%) of these patients were scored as "low probability" by 4Ts score and none had a positive SRA. Of 49 patients who underwent SRA testing because of thrombocytopenia, only 2 (4.1%; 0.5-14.0) had a positive SRA (1 with a moderate 4Ts score and 1 with a high 4Ts score). Therefore, the overall incidence of HIT confirmed by SRA was 2 (0.4%) of 528 (0.04%-1.4%).
Significant thrombocytopenia during heparin administration occurred in 9.5% of critically ill patients, but HIT was confirmed in only 4.1% of those undergoing testing, for an overall incidence of 0.4%. A low 4Ts score occurred in 78% of patients investigated for HIT; none of these patients had a positive SRA. We conclude that HIT is uncommon in critically ill patients and that the 4Ts score is worthy of further evaluation in this patient population.
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ABSTRACT: Thrombocytopenia occurs in 20% to 45% of critically ill medical-surgical patients. The 4Ts heparin-induced thrombocytopenia (HIT) score (with 4 domains: Thrombocytopenia, Timing of thrombocytopenia, Thrombosis and oTher reason[s] for thrombocytopenia) might reliably identify patients at low risk for HIT. Interobserver agreement on 4Ts scoring is uncertain in this setting. To evaluate whether a published clinical prediction rule (the "4Ts score") reliably rules out HIT in "low-risk" intensive care unit (ICU) patients as assessed by research coordinators (who prospectively scored) and 2 adjudicators (who scored retrospectively) during an international heparin thromboprophylaxis trial (PROTECT, NCT00182143). Of 3746 medical-surgical ICU patients in PROTECT, 794 met the enrollment criteria for this HIT substudy. Enrollment was predicated on one of the following occurring in ICU: platelets less than 50 × 10(9)/L, platelets decreased to 50% of ICU admission value (if admission value <100 × 10(9)/L), any venous thrombosis, or if HIT was otherwise clinically suspected. Independently, 4Ts scores were completed in real time by research coordinators blinded to study drug and laboratory HIT results, and retrospectively by 2 adjudicators blinded to study drug, laboratory HIT results, and research coordinators' scores; the adjudicators arrived at consensus in all cases. Of the 763 patients, 474 had a central or local laboratory HIT test performed and had 4Ts scoring by adjudicators; 432 were scored by trained research coordinators. Heparin-induced thrombocytopenia was defined by a centrally performed positive serotonin release assay (SRA). Of the 474 patients with central adjudication, 407 (85.9%) had a 4Ts score of 3 or lower, conferring a low pretest probability (PTP) of HIT; of these, 6 (1.5% [95% confidence interval, 0.7%-3.2%) had a positive SRA. Fifty-nine (12.4%) had a moderate PTP (4Ts score of 4-5); of these, 4 (6.8%) had a positive SRA. Eight patients had a high PTP (4Ts score of ≥6); of these, 1 (12.5%) had a positive SRA. Raw agreement between research coordinators and central adjudication on each domain of the 4Ts score and low, intermediate, and high PTP was good. However, chance-corrected agreement was variable between adjudicators (weighted κ values of 0.31-0.93) and between the adjudicator consensus and research coordinators (weighted κ values of 0.13 and 0.78). Post hoc review of the 6 SRA-positive cases with an adjudicated low PTP demonstrated that their scores would have been increased if the adjudicators had had additional information on heparin exposure prior to ICU admission. In general, the fourth domain of 4Ts (oTher causes of thrombocytopenia) generated the most disagreement. Real-time 4Ts scoring by research coordinators at the time of testing for HIT was not consistent with 4Ts scores obtained by central adjudicators. The results of this comprehensive HIT testing highlight the need for further research to improve the assessment of PTP scoring of HIT for critically ill patients.Journal of critical care 02/2014; · 2.13 Impact Factor
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ABSTRACT: The diagnosis of heparin-induced thrombocytopenia (HIT) is challenging. Over-diagnosis and over-treatment are common. To develop a pre-test clinical scoring model for HIT based on broad expert opinion that may be useful in guiding clinical decisions regarding therapy. A pre-test model, the HIT Expert Probability (HEP) Score, was constructed based on the opinions of 26 HIT experts. Fifty patients referred to a reference laboratory for HIT testing comprised the validation cohort. Two hematology trainees scored each patient using the HEP Score and a previously published clinical scoring system (4 T's). A panel of three independent experts adjudicated the 50 patients and rendered a diagnosis of HIT likely or unlikely. All subjects underwent HIT laboratory testing with a polyspecific HIT ELISA and serotonin release assay (SRA). The HEP Score exhibited significantly greater interobserver agreement [intraclass correlation coefficient: 0.88 (95% CI 0.80-0.93) vs. 0.71 (0.54-0.83)], correlation with the results of HIT laboratory testing and concordance with the diagnosis of the expert panel (area under receiver-operating curve: 0.91 vs. 0.74, P = 0.017) than the 4 T's. The model was 100% sensitive and 60% specific for determining the presence of HIT as defined by the expert panel and would have allowed for a 41% reduction in the number of patients receiving a direct thrombin inhibitor (DTI). The HEP Score is the first pre-test clinical scoring model for HIT based on broad expert opinion, exhibited favorable operating characteristics and may permit clinicians to confidently reduce use of alternative anticoagulants. Prospective multicenter validation is warranted.Journal of Thrombosis and Haemostasis 12/2010; 8(12):2642-50. · 6.08 Impact Factor