title: Suspicion of heparin-induced thrombocytopenia in internal medicine: How appropriate is the ordering of anti-PF4/heparin antibody testing?
abstract: Thrombocytopenia is frequent in hospitalized patients, and heparin-induced thrombocytopenia (HIT) is often suspected when a decrease in platelet count is concomitant with heparin treatment. ELISA tests used for anti-PF4/heparin antibodies detection usually have high sensitivity but only fair specificity for HIT. Pre-test probability scores (such as 4 Ts or HEP scores) have been validated and a low probability score rules out HIT without anti-PF4/heparin testing. The aims of this study are to evaluate the appropriateness of anti-PF4/heparin testing according to pre-test probabilities of HIT and to compare the abilities of the 4 Ts and HEP scores to avoid inappropriate anti-PF4/heparin testing. This retrospective observational study included 74 consecutive patients hospitalized in a general internal medicine division who had anti-PF4/heparin testing for suspicion of HIT. 4 Ts and HEP scores were computed retrospectively. About 73% of patients who had ordering of an anti-PF4/heparin were at low risk according to the 4 Ts score, and 46% according to the HEP score. Heparin was discontinued in 61% and 62% of low-risk patients according to 4 Ts and HEP scores and switched to alternative anticoagulant in 31% and 32% of them, respectively. No case of HIT was diagnosed in patients with a low-risk score. One major bleeding and no thrombosis were observed. For the 4 Ts score, the sensitivity was 100%, the negative predictive value (NPV) was 100%, the specificity was 77%, and the positive predictive value (PPV) was 20% (95% CI: 7-44). For the HEP score, the sensitivity was 100%, the NPV was 100%, the specificity was 49%, and the PPV was 10%. In conclusion, pre-test probability scores were vastly underused in this internal medicine population despite their ability to rule out HIT without laboratory testing in a large proportion of patients. Appropriate use of those instruments should be actively promoted.
authors.affiliation: a Division of General Internal Medicine .
authors.forename: Yan
authors.initials: Y
authors.lastname: Beauverd
authors.forename: Françoise
authors.initials: F
authors.lastname: Boehlen
authors.forename: Elena
authors.initials: E
authors.lastname: Tessitore
authors.forename: Eric
authors.initials: E
authors.lastname: Gerstel
authors.forename: Pierre
authors.initials: P
authors.lastname: Fontana
authors.forename: Mathieu
authors.initials: M
authors.lastname: Nendaz
authors.forename: Arnaud
authors.initials: A
authors.lastname: Perrier
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Reny
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D007388:Internal Medicine; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D010978:Platelet Factor 4 / Q000276:immunology; D012189:Retrospective Studies; D013921:Thrombocytopenia / Q000097:blood / Q000175:diagnosis* / Q000209:etiology*
chemical_list: D001323:Autoantibodies; D010978:Platelet Factor 4; D006493:Heparin
keywords: Anti-PF4/heparin antibodies; heparin-induced thrombocytopenia; medical decision making; pre-test probability scores; quality assessment