Objective: To characterize the use of cystatin C (cysC) across and within hospitals. Patients and Methods: This 2-part study first evaluated access to cysC testing across 129 hospitals in the state of Minnesota, using a telephone-based survey. Second, granular data from a single center (Mayo Clinic) with on-site, rapid-turnaround testing (<1 day) and automated estimated glomerular filtration rate (eGFR) reporting was used to describe temporal patterns. The characteristics of hospitals that offered cysC testing and of patients who underwent rapid cysC testing at Mayo Clinic between January 1, 2011, and March 31, 2018, were described. Poisson regression analyzed temporal trends in cysC testing. Results: Of the 114 hospitals (88%) that responded to the statewide survey, cysC was available in 91 (80%), but only 3 of 91 (3%) reported a turnaround time of <1 day. At Mayo Clinic, cysC use increased from 0.74 tests per 1000 patient-days in 2011 to 14 tests per 1000 patient-days in 2018 (P=.004). Of the 3774 patients with cysC tests, the mean first available eGFR was 46 mL/min per 1.73 m2 using cysC and 59 mL/min per 1.73 m2 using serum creatinine (P<.001). CysC testing was used across all intensities of care and was ordered by a variety of specialties. Nephrology was consulted in only 42% of cases. Conclusion: In the hospital, rapid-turnaround cysC testing is necessary for practical use but was not widely available in Minnesota. When available, a marked increase in cysC testing was observed over the study timeframe. Additional research is needed to determine optimal strategies for implementation of cysC within hospitals.
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