The Association Between Hemoglobin Level and Cognitive Function in Older Adults During Hospitalization: A Prospective Observational Study

Background and Aims In the ambulatory setting, mildly low hemoglobin (Hb), < 13 g/dL in men or < 12 g/dL in women, is associated with reduced cognition. However, in hospitalized patients, clinicians tolerate much lower Hb levels due to restrictive transfusion policies. Older adults who are at higher risk for cognitive impairment may also be particularly susceptible to impaired cognition from lower Hb levels. The purpose of this study was to test for an association between restrictive Hb levels during hospitalization and patient's cognitive function, particularly in older adults. Methods The data for this study came from an ongoing prospective observational study of hospitalized general medicine patients at the University of Chicago Medical Center (UCMC). Any adult with a Hb < 10 g/dL between March 2017 and February 2020 was eligible. Cognition was measured using the Short Portable Mental Status Questionnaire (SPMSQ), which ranges from 0 to 10. Higher scores indicate worse cognition. Zero‐inflated Poisson (ZIP) and logistic regression were used to test the association between cognition as the dependent variable, measured by the SPMSQ, and patients' nadir Hb and age as predictor variables, controlling for race, sex, Charlson Comorbidity Index, transfusion, and a diagnosis of dementia. Results The SPMSQ questionnaire was completed by 5112 patients who had Hb < 10 g/dL. Lower nadir Hb levels were associated with decreased cognition (higher SPMSQ). Across all ages, a 1 g/dL decrease in Hb was associated with a 7.2% increase in SPMSQ score (95% confidence interval (CI) = 2.9%–11.7%). The effect of decreasing Hb on cognition was greater in older populations, where a 1 g/dL decrease in Hb was associated with an 8.8% (3.1%–14.8%) and 20.8% (9.7%–33.0%) increase in SPMSQ score for patients above 50 and 65, respectively. Conclusions Lower Hb levels during hospitalization are associated with decreased cognition, especially in older adults.