The study by Houlind et al.1 demonstrates that an abnormally low eGFRcystatin C-eGFRcreatinine ratio in hospitalized older Danish adults is associated with not only lower kidney function, but also with higher rates of malnutrition and greater established comorbidity. This agrees with the greater morbidity previously noted in several studies of patients with a low eGFRcystatin C-eGFRcreatinine ratio2, which might contribute to the strong increase in mortality also noted in such patients2. However, the greater morbidity of some patients with a low eGFRcystatin C-eGFRcreatinine ratio, cannot explain the high hazard ratio for death of individuals with a low eGFRcystatin C-eGFRcreatinine ratio in “healthy” populations with no comorbidities and no KDIGO-criteria for kidney disease2.