Are We Doing Too Many HIT Tests? II

Results of a study to determine the utility of combining laboratory values and clinical probability scores to improve the detection of heparin-induced thrombocytopenia (HIT) are reported. In a retrospective, single-site, chart review-based investigation, 156 cases in which patients with suspected HIT had positive results on a widely used diagnostic test (the anti-heparin/platelet factor 4, or anti-PF4, assay) were identified; in all cases, the blood specimens had been sent to a reference laboratory for confirmation of HIT via serotonin release assay (SRA). After investigator scoring of the clinical probability of HIT in each case by the 4T's method, a multiple logistic regression model was used to evaluate the combined effect of 4T's scores and anti-PF4 assay values in predicting SRA results. 4T's scores indicating an intermediate or high probability of HIT combined with high anti-PF4 test values (i.e., optical density [OD] value of ≥1.4) were strongly predictive of a positive SRA result, as were high-probability 4T's scores alone. Low-probability 4T's scores alone or in combination with anti-PF4 OD values of <1.4 were highly correlated with negative SRA results. Controlling for potential confounding factors, logistic regression analysis indicated that the 4T's score was a better predictor of SRA results than the anti-PF4 test value. The combination of anti-PF4 OD values and 4T's scores accurately predicted SRA results, suggesting that the SRA may not be necessary to confirm HIT in patients with a relatively low 4T's score and a low anti-PF4 OD value.

Evaluation of the Pre-Test Scoring System (4Ts) for the Evaluation and Management of Heparin Induced Thrombocytopenia

Combination Of 4T's Score and Rapid Gel Centrifugation Assay Excludes HIT In a Prospective Cohort Study

Low Pre-Test Probability Scores Are Not Sufficient to Exclude Heparin-Induced Thrombocytopenia in Critically Ill Patients

Evaluation of a Rapid and Automated Heparin-Induced Thrombocytopenia Immunoassay

AORTIC THROMBOSIS AFTER CARDIAC SURGERY FROM HEPARIN-INDUCED THROMBOCYTOPENIA

A Novel PF4-Dependent P-Selectin Expression Assay (PEA) Facilitates Early Detection of Pathogenic HIT Antibodies: Implications for Diagnosis and Treatment of HIT

Quality and Value-Focused Decision Making in Heparin-Induced Thrombocytopenia: The Impact of the American Society of Hematology's Choosing Wisely Initiative

Impact of Systems-Based Hematologists in Maintaining a HIT Program Using Continuous Clinical Audit and Education in an Academic Medical Center

Reducing Inappropriate Simultaneous Ordering of Heparin Antibody and Serotonin Release Assays.

Implementation of a Heparin-Induced Thrombocytopenia Management Program Reduces the Cost of Diagnostic Testing and Pharmacologic Treatment in an Academic Medical Center

The goal of this investigation was to understand clinicians' perceptions of the probability of pulmonary embolism as a function of V/Q scan results of normal, low, intermediate, and high probability. A questionnaire was developed and distributed to 429 clinicians at a single academic medical center. The response rate was 44% (188 of 429). The questions included level of training, specialty, probability of PE given 1 of the 4 V/Q scan results, and estimations of the charges for V/Q scanning and pulmonary angiography, and estimations of the risks of pulmonary angiography. The medians and ranges for the probability of pulmonary embolism given a normal, low, intermediate, and high probability V/Q scan result were 2.5% (0-30), 12.5% (0.5-52.5), 41.25% (5-75), and 85% (5-100), respectively. Eleven percent (21 of 188) of the respondents listed the probability of PE in patients with a low probability V/Q scan as being 5% or less, and 33% (62 of 188) listed the probability of PE given an intermediate probability scan as 50% or greater. The majority correctly identified the rate of serious complications of pulmonary arteriography, but many respondents underestimated the charge for V/Q scans and pulmonary arteriography. A substantial minority of clinicians do not understand the probability of pulmonary embolism in patients with low and intermediate probability ventilation-perfusion scans. More quantitative reporting of results is recommended. This could be particularly important because VQ scans are used less frequently but are still needed in certain clinical situations.

IntroductionHeparin-induced thrombocytopenia (HIT) results from antibodies to PF4/heparin complexes and clinical diagnosis is difficult. We evaluated the particle immunofiltration anti-platelet factor 4 (PIFA) rapid assay, in conjunction with a clinical risk score, in the diagnosis of HIT.MethodsWe performed a prospective observational study in all patients admitted to the medical intensive care unit (MICU) in a large academic medical center. Patients were screened daily for thrombocytopenia defined as either a platelet count that decreased by at least 33% or an absolute platelet count less than 150,000/μL. Patients with suspected HIT underwent PIFA and ELISA testing for anti-PF4/heparin antibodies. Available residual frozen sera were sent to a reference laboratory for serotonin release assay (SRA) testing.ResultsDuring the study period, 340 patients were admitted to the MICU, of which 143 patients met criteria for thrombocytopenia. Forty-three patients had no evidence of recent heparin exposure. PIFA and ELISA testing were performed on 100 patients, of which 92 had samples available for SRA analysis. PIFA results were negative in 62, positive in 28 and inconclusive in 2 patients. The 4Ts score showed low to intermediate risk in 57 of the PIFA negative patients. The ELISA results were negative in 86 and positive in 6 patients. SRA testing identified 3 patients with a positive SRA test and 89 patients with a negative result. All patients with a negative PIFA result also had a negative SRA result. In the one patient deemed to have clinical HIT, the pretest probability was high (4Ts score of 6) and the anti-PF4/heparin antibody testing revealed a positive SRA, inconclusive PIFA and a negative ELISA result.ConclusionsWhile thrombocytopenia in our population is common, the prevalence of HIT is low. The combination of a low to intermediate pretest probability with a negative PIFA test can rapidly exclude the presence of platelet activating anti-PF4/heparin antibodies and, therefore, HIT as the cause of the thrombocytopenia. Since a positive PIFA result has a low positive predictive value, a positive PIFA is not diagnostic of HIT and additional evaluation is warranted.

Heparin-induced thrombocytopenia (HIT) in 2011: An epidemic of overdiagnosis

Outcomes Of Platelet Transfusion In Heparin Induced Thrombocytopenia Patients