Evaluation of guidelines for ordering prothrombin and partial thromboplastin times

Objectives: Existing clinical practice guidelines for ordering prothrombin time (PT) and partial thromboplastin time (PTT) tests in the emergency department (ED) include physician expectation of an invasive procedure as a criterion. This study sought to determine whether this criterion accurately identifies patients who undergo an invasive procedure and whether an amalgam of these guidelines identifies patients at low risk of an adverse medical outcome. Methods: A prospective observational cohort study of adults treated in a university medical center ED between July 1997 and March 1998. Physicians were surveyed at order placement to determine the presence of guideline criteria. Adverse clinical outcomes defined as an International Normalized Ratio [INR] > 1.3 or PTT > 39.9 seconds combined with consequent directed medical therapy were abstracted from ED and the first 24 hours of inpatient medical records. Results: The sensitivity of ED physician expectation of an invasive procedure was 60.0%; therefore, it was excluded from both the PT and PTT guidelines. There were 553 patients with a PT test order; test order indications were absent in 190 (34.4%), of which one (0.5%, 95% CI = 0.1% to 2.9%) had adverse outcomes. There were 547 patients with a PTT test; test order indications were absent in 226 (41.3%), of which three (1.3%, 95% CI = 0.4 to 3.8%) had adverse outcomes. All three were taking warfarin when they presented to the ED. Conclusions: Emergency department physician expectation of an invasive procedure for patients with PT or PTT test orders is an insensitive predictor of patients who undergo such procedures. Clinical practice guidelines that exclude this criterion identify ED patients at the time of ED presentation at low risk for adverse medical outcomes in the ED or shortly after admission.