The incidence of hypertensive (HTN) crises in older adults has more than doubled over the past two decades. ICD-10 introduced codes for HTN urgency and emergency, but their validity has not been evaluated. We analyzed a 20% national sample of fee-for-service Medicare beneficiaries aged ≥66 years (2016-2019). Medical records were reviewed for 220 randomly sampled emergency department visits or hospitalizations with a primary ICD-10 HTN crisis code (100 HTN urgency [I16.0], 100 HTN emergency [I16.1] and 20 unspecified [I16.9]). Physicians abstracted and adjudicated cases. Two gold standards (GS) were used: (1) treating physician diagnosis and (2) adjudicated diagnosis based on BP (SBP ≥180 mmHg or DBP ≥110 mmHg), with or without end-organ damage. PPVs and 95% confidence intervals were estimated. Among 220 charts sampled from 53,100 HTN crisis cases (mean age 73 years; 33% male; 66% White), PPV for HTN emergency (I16.1) was 91% (95% CI, 85%-96%) using the treating physician GS and 78% (95% CI, 71%-86%) using the adjudicated GS. PPV for HTN urgency (I16.0) was 97% (95% CI, 93%-99%) and 81% (95% CI, 72%-88%), respectively. Overall PPV for any HTN crisis (I16.X) using the adjudicated GS was 95% (95% CI, 91%-97%). Including unspecified codes reduced PPV to 86% (95% CI, 79%-92%) and 78% (95% CI, 71-86%). ICD-10 HTN crisis codes demonstrate high PPV, supporting their use in epidemiologic and health services research.

Background:Attaining the Paris Agreement goal of limiting global temperature rise to below 1.5-2 °C requires the healthcare sector to achieve net-zero emissions by 2050. This necessitates adopting diverse strategies, including replacing carbon-intensive metered-dose inhalers (MDIs) with more environmentally sustainable dry powder inhalers (DPIs) and soft mist inhalers (SMIs). While several European countries have successfully made this transition, patterns of MDI use and barriers to adopting sustainable alternatives in the United States remain poorly understood. Thus, we assessed inhaler utilization, costs, and insurance coverage among U.S. older adults. Methods:Using 100% fee-for-service Medicare data with pharmacy benefit (2008-2022), we described utilization trends and costs by device types and drug classes, including inhaled corticosteroids [ICS] and short-/long-acting beta-agonists [S/LABA]. Using the COVERAGE Search database, we extracted formulary data from Part D plans in 10 large US states and described insurance coverage, formulary tier placement (categorizing drugs by costs), prior authorization (requiring insurer approval for coverage), and step therapy (requiring initial trial of lower-cost drugs). Findings:Of 160,845,280 inhalers dispensed to 10,494,068 older adults (mean age 74 ± 7 years; 38% male; 85% White), 51% were MDIs. Of these MDIs, 88% were SABA and ICS. Median deductible-phase out-of-pocket costs were $3-9 for SABA MDIs vs. $42-49 for DPIs/SMIs and $3-4 for ICS MDIs vs. $3-116 for DPIs/SMIs. Only 18% and 50% of 2530 Part D plans covered SABA and ICS DPIs, respectively. Among the covering plans, >70% placed DPIs for SABA or ICS in higher-cost tiers, with 32-58% requiring prior authorization or step therapy. Interpretation:MDIs, primarily as SABA or ICS, accounted for over half of inhalers dispensed to US older adults. Most insurance plans excluded sustainable alternatives for SABA/ICS. When covered, additional approval steps and/or higher patient costs were posed. Multi-level efforts are needed to ensure affordable access to sustainable alternatives, as demonstrated in European countries. Funding:Funding for this study was provided by the National Institutes of Health and the National Institute on Aging (1R01AG060232-01A1).

Background:With rising temperatures and an aging population, understanding how to prevent heat-related illness among older adults will be increasingly crucial. Despite biological plausibility, no study to date has investigated how exposure to fine particulate matter air pollution (PM2.5) may contribute to the risk of hospitalization with a diagnosis code indicating heat-related illness, referred to as heat-related hospitalization. This study aims to fill this gap by investigating the independent and combined effects of temperature and PM2.5 exposures on heat-related hospitalization risk. Methods:We identified Medicare fee-for-service beneficiaries in the contiguous United States who experienced a heat-related hospitalization between 2008 and 2016. Using a case-crossover design and fitting Bayesian conditional logistic regression models, we characterized the associations of temperature and PM2.5 exposures with heat-related hospitalization. We then estimated the relative excess risk due to interaction to quantify the additive-scale interaction of simultaneous exposure to heat and PM2.5. Results:We observed 112,969 heat-related hospitalizations among 29,345,820 Medicare beneficiaries in the study sample. Fixing PM2.5 at the case day median, the odds ratio for increasing temperature from its case day median to the 95th percentile was 1.05 (95% CI: 1.03, 1.06). Fixing temperature at the case day median, the odds ratio for increasing PM2.5 from its median to the 95th percentile was 1.01 (95% CI: 0.99, 1.04). The risk due to interaction for simultaneous median-to-95th percentile increases in temperature and PM2.5 was 0.03 (95% CI: 0.01, 0.06). Conclusions:Our study is the first to observe synergism between temperature and PM2.5 exposures associated with the risk of heat-related hospitalization. These findings highlight the importance of considering air pollution in effective public health and clinical interventions to prevent heat-related illness.

Introduction: Numerous studies have shown a U-shaped relationship between ambient temperature and cardiovascular mortality. However, few studies examined a temperature- heart failure (HF) hospitalization relationship or its regional variations in the United States (US). Research Question: How does ambient temperature impact HF hospitalizations in older US adults? Does the temperature-HF relationship vary by region? Methods: We conducted a place and time-stratified case-crossover study of older adults (age ≥ 66 years) hospitalized for HF between 2007-2022 using 20% national Medicare data. Daily mean temperatures (T mean ) were identified from the Parameter-elevation Relationships on Independent Slopes Model linked through residential zip code. HF cases were defined as hospitalization with a primary HF diagnosis. Up to 5 controls were selected as same day of week, month, and year as cases. We used conditional logit for distributed lag non-linear models in overall population and subgroups by region (Northeast, West, South, Midwest). We used 14-day lag for the primary analysis, which was varied from 2-28 days. Results: Among 1,517,756 HF hospitalization cases, the effect of cold T mean on HF hospitalizations is delayed and peaked ~4-8 days after exposure; the risk ratio (RR) of temperatures < 50°F vs. 65°F ranged from 1.01-1.07 (Figure 1). The cumulative risk of colder T mean were only significant in longer lag models (24°F vs. 65°F –lag 7: RR 0.98 [0.96–1.00]; lag 14: RR 1.06 [1.03–1.08]; lag 21: RR 1.1[1.07–1.13]). Overall, heat had minimum and non-significant effects that were near immediate (lag 0-2) (Figure 1). In regional analyses (Figure 2), the magnitude of colder T mean effect varied (23°F vs. 65°F – Northeast: RR 0.96[0.92–1.01]; West: RR 1.34[1.21–1.50]; South: RR 1.01[0.96–1.06]; Midwest: RR 1.08[1.03–1.13]) The effect of high T mean also varied; heat had non-significant increase in HF hospitalization in the Northeast region only with max RR of 1.42 (100°F vs. 65°F). Conclusion: Colder T mean was associated with increased HF hospitalizations. The elevated risk was apparent approximately 4 days after exposure; the magnitude varied by region. Extreme heat’s association with HF hospitalization was indicated in Northeast region and confined within 0-2 days after exposure. The regional variation may reflect acclimatization to regional climate, available local resources, and varied behavioral responses to temperature.

Abstract Background: Fine Particulate Matter (PM2.5) is associated with higher mortality among people with chronic conditions. Breast cancer (BC) survivors may be particularly vulnerable during cancer treatment. We assessed the association between PM2.5 during 9-months following BC diagnosis and all-cause and BC-mortality using policy relevant PM2.5 cut-offs. Methods: Using SEER-Medicare linked with a high-resolution model-based PM2.5 by residential zipcode (2007-2016), we assembled a cohort of women ≥66 years with incident stage I-IV BC. We assessed PM2.5 exposure, categorized as <8 µg/m3 (low), 8-12 µg/m3 (moderate) and >12 µg/m3 (high—above air quality standard), and types of cancer treatments (surgery [SX], chemotherapy [CTX], radiation therapy [RTX]) during a 9-month landmark period. We identified all-cause and BC death within 5 years of diagnosis. We fit multivariable Cox proportional hazard models to assess associations with PM2.5 exposure adjusting for individual-level characteristics (demographics, tumor characteristics, comorbidities), neighborhood SES, SEER state, and long-term PM2.5 exposure. We also evaluated the association between PM2.5 exposure and mortality by treatment types (SX, SX + RTX, SX + CTX, SX + RTX + CTX, and RTX and/or CTX). We used multiple imputation to account for missing variables (race, ER status, HER2 status, grade). Results: Among 72,798 women (mean age 75 years, 83% white, 56% stage I, 32% II, 9.2% III, 2.9% IV), 41%, 32%, 13%, 8.4%, and 5.1% received SX + RTX, SX only, SX + Chemo + RTX, SX + Chemo, and CTX and/or RTX. The mean PM2.5 level was 8.8 µg/m3 [36%, 52% and 11% were exposed to <8, 8-12, and >12, respectively]. We observed 12,163 all-cause and 4,729 BC deaths during follow-up. Compared to those exposed to low levels, higher levels of PM2.5 exposure were associated with increased all-cause mortality for both moderate PM2.5 [HR 1.03 (95%CI:1.00-1.05)] and high PM2.5 [HR 1.09 (95%CI: 1.06-1.14)] but not BC-specific mortality. Among treatment subgroups, PM2.5 was associated with higher all-cause mortality in SX+RTX for moderate [HR 1.24 (95%CI:1.18-1.32)] and high PM2.5 [HR 1.36 (95%CI: 1.25-1.48)] and SX+RTX+CTX for high PM2.5 [HR 1.33 (95%CI: 1.17-1.51)]. There were no association between moderate/high PM2.5 with all-cause mortality in SX only and SX+CTX. Among the SX+RTX subgroup, BC-specific mortality was elevated for both moderate [HR 1.50 (95%CI:1.35-1.66)] and high PM2.5 [HR 1.81 (95%CI: 1.55-2.12)]. Conclusion: Even below EPA regulatory thresholds (PM2.5 <12 µg/m3), we observed increased risk of death in BC survivors who had high PM2.5 exposure during treatment period. The elevated mortality primarily occurred among women who received RTX and was present for all-cause and BC-specific mortality. The potential interaction between RTX and PM2.5 exposure, even after adjusting for tumor subtype and stage, warrants further evaluation. Citation Format: Benjamin Bates, Rachel Nethery, Melanie Rua, Hari Iyer, Elisa Bandera, Soko Setoguchi. Fine particulate matter exposure during breast cancer treatment among older women associated with increased mortality [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 841.

IMPORTANCE:Despite biological plausibility, very few epidemiologic studies have investigated the risks of clinically significant bleeding events due to particulate air pollution. OBJECTIVE:To measure the independent and synergistic effects of PM2.5 exposure and anticoagulant use on serious bleeding events. DESIGN:Retrospective cohort study (2008-2016). SETTING:Nationwide Medicare population. PARTICIPANTS:A 50% random sample of Medicare Part D-eligible Fee-for-Service beneficiaries at high risk for cardiovascular and thromboembolic events. EXPOSURES:Fine particulate matter (PM2.5) and anticoagulant drugs (apixaban, dabigatran, edoxaban, rivaroxaban, or warfarin). MAIN OUTCOMES AND MEASURES:The outcomes were acute hospitalizations for gastrointestinal bleeding, intracranial bleeding, or epistaxis. Hazard ratios and 95% CIs for PM2.5 exposure were estimated by fitting inverse probability weighted marginal structural Cox proportional hazards models. The relative excess risk due to interaction was used to assess additive-scale interaction between PM2.5 exposure and anticoagulant use. RESULTS:The study cohort included 1.86 million high-risk older adults (mean age 77, 60% male, 87% White, 8% Black, 30% anticoagulant users, mean PM2.5 exposure 8.81 μg/m3). A 10 μg/m3 increase in PM2.5 was associated with a 48% (95% CI: 45%-52%), 58% (95% CI: 49%-68%) and 55% (95% CI: 37%-76%) increased risk of gastrointestinal bleeding, intracranial bleeding, and epistaxis, respectively. Significant additive interaction between PM2.5 exposure and anticoagulant use was observed for gastrointestinal and intracranial bleeding. CONCLUSIONS:Among older adults at high risk for cardiovascular and thromboembolic events, increasing PM2.5 exposure was significantly associated with increased risk of gastrointestinal bleeding, intracranial bleeding, and epistaxis. In addition, PM2.5 exposure and anticoagulant use may act together to increase risks of severe gastrointestinal and intracranial bleeding. Thus, clinicians may recommend that high-risk individuals limit their outdoor air pollution exposure during periods of increased PM2.5 concentrations. Our findings may inform environmental policies to protect the health of vulnerable populations.

e14607 Background: There is biologic plausibility that antibiotics (ABX) may reduce the effectiveness of cancer therapy, most notably immune checkpoint inhibitors (ICI). As ABX are commonly prescribed to older persons and more than a third of US persons with cancer are eligible for ICIs, use of ABX has important population health implications. We assess the association between ABX use and mortality among persons with NSCLC who receive first-line (1L) treatment. Methods: Using SEER-Medicare, we assembled a cohort of persons ≥66 years with NSCLC who received 1L treatment with platinum-based chemotherapy (PLT) or ICI (PLT without ICI, PLT with ICI, and ICI monotherapy) within one year of cancer diagnosis between 2017-2019. We assessed overall ABX exposure from 1 month to 1 year prior to treatment initiation and by ABX class. Primary outcome was all cause deaths within three years of treatment initiation or until 12/31/2020. Multivariable Cox proportional hazard models adjusting for individual-level characteristics (demographics, time-to-treatment, comorbidities, healthcare use, SEER registry, and neighborhood socioeconomic status) and landmark analyses of 1-6 months after cancer treatment were used to assess the association between ABX exposure and mortality. Results: Among 4,182 persons (mean age 75 years, 85% white, 68% chemo-immunotherapy within 2 months of NSCLC diagnosis), 63%, 18%, and 18% received PLT, PLT+ICI, and ICI, respectively. ICI+/-PLT increased in prevalence from 20% of treatments (2017) to 55% (2019). The mean age of persons who received ICI alone (78 years old) was higher than PLT or PLT+ICI. Prior to 1L treatment, 22% and 72% of persons received ABX within 30 days and 1 year prior to cancer treatment, respectively. The three most common ABX classes were fluoroquinolones (48%), penicillins (21%), and macrolides (18%). The cohort was followed for 3,274 person-years and included 2,958 deaths within 1 year and 4,144 deaths within 3 years of follow-up. Compared with persons who did not receive ABX within 3 months of cancer treatment, ABX use was associated with higher risk of death within 3 years for ICI alone [HR 1.24 (1.05-1.46) but not for PLT alone or PLT+ICI. Fluoroquinolones were associated with an elevated risk of mortality among persons who received ICI alone HR 1.41(95%CI: 1.1-1.8) and PLT alone HR 1.18 (95%CI: 1.05-1.32) but not PLT+ICI. Our findings were similar across definitions of ABX exposure (30 days to 1 year prior to treatment) and analytic landmarks after treatment initiation. Conclusions: Among patients with NSCLC who received 1L treatment, we identified an association between ABX exposure prior to treatment and increased mortality among persons who received ICI monotherapy but not PLT+ICI. As ICIs expand to more cancer types and earlier stages, ABX use may have a significant impact on outcomes and population health.

BACKGROUND:The Cystic Fibrosis Foundation Patient Registry (CFFPR) provides valuable clinical and demographic data but includes limited information on health services and medications provided outside of CF Care Centers. Linking CFFPR to claims databases such as national Medicaid data could address these data gaps. METHODS:Linkage algorithms based on state of residence, gender, and date of birth were utilized to match individuals with CF diagnostic codes in national Medicaid databases (2016) to individuals in the CFFPR (2015-2016). Subsets of individuals with partial social security numbers or residing in the state of North Carolina were utilized to validate the accuracy of linkages and perform exploratory analyses on care utilization and costs. RESULTS:Of the 32,152 individuals in CFFPR, 10,616 were uniquely linked to national Medicaid databases. The 372 linked individuals within the NC extract had 8.0 ± 7.6 visits to outpatient providers, substantially higher than the 4.2 ± 2.4 CF Care Center outpatient visits documented within CFFPR. Similarly, linked individuals had 2.1 ± 1.7 oral antibiotic prescriptions within CMS pharmacy databases versus 0.5 ± 1.9 oral antibiotic prescriptions in CFFPR. Total pharmacy costs for the linked individuals in NC were $16.4 million, with pancrealipase (19 %), dornase alfa (24 %), and CFTR modulators (29 %) the largest expenditures. Total non-pharmacy costs were $7.5 million, with inpatient hospitalization representing 53 % of costs. CONCLUSION:Linkage of data from Medicaid and CFFPR can produce valid comprehensive data on low-income people with CF and provide opportunities to examine utilization/adherence or comparative effectiveness and safety of medications as well as conduct economic analyses in the low-income CF population.

Background:Multiple studies from countries with relatively lower PM 2.5 level demonstrated that acute and chronic exposure even at lower than recommended level, e.g., 9 μg/m 3 in the US increased the risk of cardiovascular (CV) events. However, limited studies using individual level data exist from countries with a wider range of PM levels to illustrate shape of the exposure-response curve throughout the range including > 20 μg/m 3 PM 2·5 concentrations. Taiwan with its policies reduced PM 2.5 over time provide opportunities to illustrate the dose response curves and how reductions of PM 2.5 over time correlated with CV events incidence in a nationwide sample. Methods:Using data from the 2009-2019 Taiwan National Health Insurance Database linked to nationwide PM2.5 data. We examined the shape and magnitude of the exposure-response curve between seasonal average PM 2·5 level and CV events-related hospitalizations among older adults at high-risk for CV events. We used history-adjusted marginal structural models including potential confounding by individual demographic factors, baseline comorbidities, and health service measures. To quantify the risk below and above 20 μg/m 3 we conducted stratified Cox regression. We also plotted PM 2.5 and CV events from 2009-2019 as well as average temperature as a comparison. Findings:Using the PM 2.5 concentration <15 μg/m 3 (Taiwan regulatory standard) as a reference, the seasonal average PM 2.5 concentration (15-23.5μg/m 3 and > 23.5 μg/m 3 ) were associated with hazard ration of 1.13 (95%CI 1.09-1.18) and 1.19 (95%CI 1.14-1.24), 1.07 (95%CI 1.03-1.11) and 1.14 (95%CI 1.10-1.18), 1.22 (95%CI 1.08-1.38) and 1.31 (95%CI 1.16-1.48), 1.04 (95%CI 0.98-1.10) and 1.10 (95%CI 1.04-1.16) respectively for HF, IS/TIA,PE/DVT and MI/ACS. A nonlinear relationship between PM 2·5 and CV events outcomes was observed at PM 2·5 levels above 20 μg/m 3 . Interpretation:A nonlinear exposure-response relationship between PM2·5 concentration and the incidence of cardiovascular events exists when PM2.5 is higher than the levels recommended by WHO Air Quality Guidelines. Further lowering PM2·5 levels beyond current regulatory standards may effectively reduce the incidence of cardiovascular events, particularly HF and DVT, and can lead to tangible health benefits in high-risk elderly population.

Objective: To measure the association between ambient heat and hypoglycemia-related ED visit or hospitalization in insulin users. Research Design and Methods: We identified cases of serious hypoglycemia among adults using insulin aged ≥65 in the US (via Medicare Part A/B/D-eligible beneficiaries) and Taiwan (via National Health Insurance Database) from June to September, 2016-2019). We then estimated odds of hypoglycemia by heat index (HI) percentile categories using conditional logistic regression with a time-stratified case-crossover design. Results: Among ~2 million insulin users in the US (32,461 hypoglycemia cases), ORs for HI >99th, 95-98th, 85 94th, and 75-84th percentiles compared to the 25-74th percentile were 1.38 (95% CI, 1.28-1.48), 1.14 (1.08-1.20), 1.12 (1.08-1.17), and 1.09 (1.04-1.13) respectively. Overall patterns of associations were similar for insulin users in the Taiwan sample (~283,000 insulin users, 10,162 hypoglycemia cases). Conclusions: In two national samples of older insulin users, higher ambient temperature was associated with increased hypoglycemia risk.

Objective: To assess the association between ambient heat and all-cause and cause-specific emergency department (ED) visits and acute hospitalizations among Medicare beneficiaries in the conterminous United States. Design: Retrospective cohort study. Setting: Conterminous US from 2008 and 2019. Participants: 2% random sample of all Medicare fee-for-service beneficiaries eligible for Parts A, B, and D. Main outcome measures: All-cause and cause-specific (cardiovascular, renal, and heat-related) ED visits and unplanned hospitalizations were identified using primary ICD-9 or ICD-10 diagnosis codes. We measured the association between ambient temperature - defined as daily mean temperature percentile of summer (June through September) - and the outcomes. Hazard ratios and their associated 95% confidence intervals were estimated using multivariable Cox proportional hazards regression, adjusting for individual level demographics, comorbidities, healthcare utilization factors and zip-code level social factors. Results: Among 809,636 Medicare beneficiaries (58% female, 81% non-Hispanic White, 24% <65), older beneficiaries (aged >= 65) exposed to >95th percentile temperature had a 64% elevated adjusted risk of heat-related ED visits (HR [95% CI], 1.64 [1.46,1.85]) and a 4% higher risk of all-cause acute hospitalization (1.04 [1.01,1.06]) relative to <25th temperature percentile. Younger beneficiaries (aged <65) showed increased risk of heat-related ED visits (2.69 [2.23,3.23]) and all-cause ED visits (1.03 [1.01,1.05]). The associations with heat related events were stronger in males and individuals dually eligible for Medicare and Medicaid. No significant differences were observed by climatic region. We observed no significant relationship between temperature percentile and risk of CV-related ED visits or renal-related ED visits. Conclusions: Among Medicare beneficiaries from 2008 to 2019, exposure to daily mean temperature >= 95th percentile was associated with increased risk of heat-related ED visits, with stronger associations seen among beneficiaries <65, males, and patients with low socioeconomic position. Further longitudinal studies are needed to understand the impact of heat duration, intensity, and frequency on cause-specific hospitalization outcomes. (c) 2024 The Authors. Published by Elsevier Inc.

Background Implantable cardioverter-defibrillator (ICD) placement in heart failure (HF) patients during or early after (≤90 days) unplanned cardiovascular hospitalizations has been associated with poor outcomes. Racial and ethnic differences in this “peri-hospitalization” ICD placement have not been well described. Methods Using a 20% random sample of Medicare beneficiaries, we identified older (≥66 years) patients with HF who underwent ICD placement for primary prevention from 2008 to 2018. We investigated racial and ethnic differences in frequency of peri-hospitalization ICD placement using modified Poisson regression. We utilized Kaplan-Meier analyses and Cox regression to investigate the association of peri-hospitalization ICD placement with differences in all-cause mortality and hospitalization (HF, cardiovascular and all-cause) within and between race and ethnicity groups for up to 5-year follow-up. Results Among the 61,710 beneficiaries receiving ICDs (35% female, 82% White, 10% Black, 6% Hispanic), 44% were implanted peri-hospitalization. Black [adjusted rate ratio (RR) 95% Confidence Interval (95% CI): 1.16 (1.12, 1.20)] and Hispanic [RR (95% CI): 1.10 (1.06, 1.14)] beneficiaries were more likely than White beneficiaries to have ICD placement peri-hospitalization. Peri-hospitalization ICD placement was associated with an at least 1.5× increased risk of death, 1.5× increased risk of re-hospitalization and 1.7× increased risk of HF hospitalization during 3-year follow-up in fully adjusted models. Although beneficiaries with peri-hospitalization placement had the highest mortality and readmission rates 1- and 3-year post-implant (log-rank p < 0.0001), the magnitude of the associated risk did not differ significantly by race and ethnicity (p = NS for interaction). Conclusions ICD implantation occurring during the peri-hospitalization period was associated with worse prognosis and occurred at higher rates among Black and Hispanic compared to White Medicare beneficiaries with HF during the period under study. The risk associated with peri-hospitalization ICD placement did not differ by race and ethnicity. Future paradigms aimed at enhancing real-world effectiveness of ICD therapy and addressing disparate outcomes should consider timing and setting of ICD placement in HFrEF patients who otherwise meet guideline eligibility.

Background: Heart failure (HF) is a leading cause of hospitalization in older adults. Medicare data have been used to assess HF outcomes. However, the validity of ICD-10 diagnosis codes (used since 2015) to identify acute HF hospitalization or distinguish reduced (heart failure with reduced ejection fraction) versus preserved ejection fraction (HFpEF) is unknown in Medicare data. Methods: Using Medicare data (2015–2017), we randomly sampled 200 HF hospitalizations with ICD-10 diagnosis codes for HF in the first/second claim position in a 1:1:2 ratio for systolic HF (I50.2), diastolic HF (I50.3), and other HF (I50.X). The primary gold standards included recorded HF diagnosis by a treating physician for HF hospitalization, ejection fraction (EF)≤50 for heart failure with reduced ejection fraction, and EF>50 for HFpEF. If the quantitative EF was not present, then qualitative descriptions of EF were used for heart failure with reduced ejection fraction/HFpEF gold standards. Multiple secondary gold standards were also tested. Gold standard data were extracted from medical records using standardized forms and adjudicated by cardiology fellows/staff. We calculated positive predictive values with 95% CIs. Results: The 200-chart validation sample included 50 systolic, 50 diastolic, 47 combined dysfunction, and 53 unspecified HF patients. The positive predictive values of acute HF hospitalization was 98% [95% CI, 95–100] for first-position ICD-10 HF diagnosis and 66% [95% CI, 58–74] for first/second-position diagnosis. Quantitative EF was available for ≥80% of patients with systolic, diastolic, or combined dysfunction ICD-10 codes. The positive predictive value of systolic HF codes was 90% [95% CI, 82–98] for EFs≤50% and 72% [95% CI, 60–85] for EFs≤40%. The positive predictive value was 92% [95% CI, 85–100] for HFpEF for EFs>50%. The ICD-10 codes for combined or unspecified HF poorly predicted heart failure with reduced ejection fraction or HFpEF. Conclusions: ICD-10 principal diagnosis identified acute HF hospitalization with a high positive predictive value. Systolic and diastolic ICD-10 diagnoses reliably identified heart failure with reduced ejection fraction and HFpEF when EF 50% was used as the cutoff.