['We examined the predictive ability of red cell distribution width (RDW) and the change in RDW during hospitalization (ΔRDW) for length of stay (LOS) and 30-day outcomes after heart failure (HF) inpatient stay.', 'Electronic query of Intermountain Healthcare medical records identified patients (N\xa0=\xa06414) with a primary diagnosis of HF who were discharged between 2004 and 2013, had RDW measured within 24\xa0h after admission, and had RDW tested at least once more during the same hospitalization. ΔRDW was defined as the last RDW within 24\xa0h prior to discharge minus the first RDW.', 'Median LOS by initial RDW quartiles was Q1: 3.0, Q2: 3.1, Q3: 3.7, and Q4: 4.0\xa0days (P-trend<0.001), and by ΔRDW quartiles was Q1: 4.1, Q2: 3.4, Q3: 3.6, and Q4: 4.7\xa0days (P-trend<0.001). Both initial RDW (16.8\xa0±\xa02.8% vs. 16.3\xa0±\xa02.7%, P\xa0<\xa00.001) and ΔRDW (0.21\xa0±\xa01.09% vs. 0.14\xa0±\xa01.04%, P\xa0=\xa00.039) predicted 30-day readmission vs. no readmit. For 30-day decedents vs. survivors, initial RDW was 17.3\xa0±\xa03.0% vs. 16.3\xa0±\xa02.6% (P\xa0<\xa00.001), while ΔRDW was +0.20\xa0±\xa01.14% vs. +0.14\xa0±\xa01.04% (P\xa0=\xa00.15).'] Are both initial red cell distribution width ( RDW ) and change in RDW during heart failure hospitalization associated with length of hospital stay and 30-day outcomes?