Toward better utilization of laboratory resources: The impact of a mandatory 4Ts pretest clinical assessment form on the diagnosis of heparin-induced thrombocytopenia

Background: Frequency rates for heparin-induced thrombocytopenia range from 0.5% to 5.0% of all heparin-treated patients. The most readily available laboratory tests are very sensitive for heparin-dependent platelet factor 4 antibodies, but are not specific for heparin-induced thrombocytopenia. Tests with greater specificity are more technically demanding and less readily available. In addition to laboratory testing, four clinical features-known as the 4Ts-are used when diagnosing this immune-mediated process: Throm bocytopenia, Timing of thrombocytopenia, Thrombosis, and exclusion of other causes of Thrombocytopenia. Methods: A study was conducted to assess the impact of a mandatory 4Ts pretest form on the appropriateness of test ordering for heparininduced thrombocytopenia. Data were collected and analyzed before and after the form was introduced at Vancouver General Hospital. Results: During the 2.5-year study period, 145 laboratory tests for heparin-induced thrombocytopenia were ordered; 65 of these were ordered before and 80 after the man - datory 4Ts pretest clinical assessment form was introduced. After the form was introduced, more tests were ordered for patients with high (6-8) 4Ts scores (8% vs 23%, P =.015) and with intermediate (4-5) 4Ts scores (40% vs 55%, NS). As well, fewer tests were ordered for pa - tients with low (1-3) 4Ts scores (24% vs 54%, P <.001) after the mandatory 4Ts pretest form was introduced. None of 53 patients with low 4Ts scores had laboratory-confirmed heparin-induced thrombocytopenia. Conclusions: The mandatory use of a 4Ts pretest clinical assessment form for diagnosis of heparin-in duced thrombocytopenia resulted in more appropriate utilization of laboratory testing, standardization of patient assessment, and better physician understanding of heparin-induced thrombocytopenia. Testing may not be indicated for patients with low 4Ts pretest scores.