BACKGROUND:Previous studies have noted a high (41%) prevalence and poor discharge summary communication of pending laboratory (lab) tests at the time of hospital discharge for general medical patients. However, the prevalence and communication of pending labs within a high-risk population, specifically those patients discharged to sub-acute care (i.e., skilled nursing, rehabilitation, long-term care), remains unknown. OBJECTIVE: To determine the prevalence and nature of lab tests pending at hospital discharge and their inclusion within hospital discharge summaries, for common sub-acute care populations. DESIGN: Retrospective cohort study. PARTICIPANTS: Stroke, hip fracture, and cancer patients discharged from a single large academic medical center to sub-acute care, 2003-2005 (N=564) MAIN MEASURES: Pending lab tests were abstracted from the laboratory information system (LIS) and from each patient's discharge summary, then grouped into 14 categories and compared. Microbiology tests were subdivided by culture type and number of days pending prior to discharge. KEY RESULTS: Of sub-acute care patients, 32% (181/ 564) were discharged with pending lab tests per the LIS; however, only 11% (20/181) of discharge summaries documented these. Patients most often left the hospital with pending microbiology tests (83% [150/181]), particularly blood and urine cultures, and reference lab tests (17% [30/181]). However, 82% (61/74) of patients' pending urine cultures did not have 24-hour preliminary results, and 19% (13/70) of patients' pending blood cultures did not have 48-hour preliminary results available at the time of hospital discharge. CONCLUSIONS: Approximately one-third of the subacute care patients in this study had labs pending at discharge, but few were documented within hospital discharge summaries. Even after considering the availability of preliminary microbiology results, these omissions remain common. Future studies should focus on improving the communication of pending lab tests at discharge and evaluating the impact that this improved communication has on patient outcomes.KEY WORDS: laboratory tests; hospital discharge; sub-acute care.